![slapped him on the shoulder, and proceeded himself with the
passage.
Many particulars of Paoli's habits are still remembered by the people
here. The old men have seen him walking about under these
chestnuts, in a long green, gold-laced coat,[N] and a vest of brown
Corsican cloth. When he showed himself, he was always surrounded
by his peasantry, whom he treated as equals. He was accessible to
all, and he maintained a lively recollection of an occasion when he
had deeply to repent his having shut himself up for an hour. It was
one day during the last struggle for independence; he was in
Sollacaro, embarrassed with an accumulation of business, and had
ordered the sentry to allow no one admission. After some time a
woman appeared, accompanied by an armed youth. The woman was
in mourning, wrapped in the faldetta, and wore round her neck a
black ribbon, to which a Moor's head, in silver—the Corsican arms—
was attached. She attempted to enter—the sentry repelled her. Paoli,
hearing a noise, opened the door, and demanded hastily and
imperiously what she wanted. The woman said with mournful
calmness: "Signor, be so good as listen to me. I was the mother of
two sons; the one fell at the Tower of Girolata; the other stands
here. I come to give him to his country, that he may supply the
place of his dead brother." She turned to the youth, and said to him:
"My son, do not forget that you are more your country's child than
mine." The woman went away. Paoli stood a moment as if
thunderstruck; then he sprang after her, embraced with emotion
mother and son, and introduced them to his officers. Paoli said
afterwards that he never felt so embarrassed as before that noble-
hearted woman.
He never married; his people were his family. His only niece, the
daughter of his brother Clemens, was married to a Corsican called
Barbaggi. But Paoli himself, capable of all the virtues of friendship,
was not without a noble female friend, a woman of talent and
glowing patriotism, to whom the greatest men of the country
confided their political ideas and plans. This Corsican Roland,](https://image.slidesharecdn.com/2151378-250601231912-627fe43f/85/Database-Design-And-Development-An-Essential-Guide-For-It-Professionals-Paulraj-Ponniahauth-77-320.jpg)
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- 6. DATABASE DESIGN AND DEVELOPMENT An Essential Guide for IT Professionals PAULRAJ PONNIAH A JOHN WILEY & SONS, INC., PUBLICATION
- 7. Copyright © 2003 by John Wiley & Sons, Inc. All rights reserved. Published by John Wiley & Sons, Inc., Hoboken, New Jersey. Published simultaneously in Canada. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning, or otherwise, except as per- mitted under Section 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400, fax 978-750- 4470, or on the web at www.copyright.com. Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, (201) 748-6011, fax (201) 748-6008, e-mail: permreq@wiley.com. Limit of Liability/Disclaimer of Warranty: While the publisher and author have used their best efforts in preparing this book, they make no representations or warranties with respect to the accuracy or com- pleteness of the contents of this book and specifically disclaim any implied warranties of merchantabil- ity or fitness for a particular purpose. No warranty may be created or extended by sales representatives or written sales materials. The advice and strategies contained herein may not be suitable for your sit- uation. You should consult with a professional where appropriate. Neither the publisher nor author shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages. For general information on our other products and services please contact our Customer Care Department within the U.S. at 877-762-2974, outside the U.S. at 317-572-3993 or fax 317-572-4002. Wiley also publishes its books in a variety of electronic formats. Some content that appears in print, however, may not be available in electronic format. Library of Congress Cataloging-in-Publication Data: Ponniah, Paulraj. Database design and development: an essential guide for IT professionals/Paulraj Ponniah. p. cm. “A Wiley-Interscience publication.” Includes bibliographical references and index. ISBN 0-471-21877-4 (cloth) 1. Database design. 2. Database management. I. Title. QA76.9.D26P58 2003 005.74—dc10 2002192402 Printed in the United States of America. 10 9 8 7 6 5 4 3 2 1
- 8. In loving memory of my dear parents.
- 9. CONTENTS Preface xxv PART I BASIC DATABASE CONCEPTS 1 1 THE DATABASE APPROACH 3 Chapter Objectives / 3 Evolution of Data Systems / 4 Technology Explosion / 5 Demand for Information / 8 Waves of Evolution / 9 File-Oriented Data Systems / 10 Why Database Systems? / 11 The Driving Forces / 11 Inadequacy of Earlier Data Systems / 12 Database Systems Meet the Challenges / 16 The Database Approach / 19 Database: A Formal Definition / 19 Data-Driven, Not Process-Driven / 20 Basic Concepts / 21 How Databases Are Used / 23 Overview of Data Models / 23 Hierarchical / 24 Network / 25 vii
- 10. Relational / 27 Object-Relational / 28 Types of Databases / 29 Centralized / 29 Distributed / 30 Survey of the Database Industry / 31 Brief History / 31 Leading Commercial Databases / 33 Peek into the Future / 33 Chapter Summary / 34 Review Questions / 34 Exercises / 35 2 OVERVIEW OF MAJOR COMPONENTS 36 Chapter Objectives / 36 What Makes Up a Database Environment? / 37 Overall Architecture / 38 Hardware Infrastructure / 40 Supporting Software / 40 People and Procedures / 41 Database and DBMS / 42 DB and DBMS – Not Synonymous / 42 Why Use a DBMS? / 42 DBMS Classifications / 45 Languages and Interfaces / 46 Functions and Features / 48 Hardware / 48 Storage of Data / 50 Operating System Software / 50 Database Software / 52 Users / 52 Practitioners / 53 Methods and Procedures / 54 How Databases Are Used / 55 Inside a DBMS / 56 Database Engine / 56 Data Dictionary / 58 Query Processor / 59 Forms Generator / 61 Report Writer / 62 Applications Developer / 63 viii CONTENTS
- 11. Communications Interface / 64 Utilities / 64 Chapter Summary / 64 Review Questions / 65 Exercises / 66 PART II DATABASE DEVELOPMENT PROCESS 67 3 SIGNIFICANCE OF THE DATABASE ENVIRONMENT 69 Chapter Objectives / 69 Organizational Context / 70 Core Business / 70 Primary Processes / 71 Information as a Major Asset / 72 DB System in the Organization / 74 Information Requirements / 75 At User Levels / 76 In Functional Divisions / 77 At Geographic Regions / 78 Providing Information / 79 Information Sharing / 80 Why Share Information? / 80 Major Benefits / 82 Information Sharing Schemes / 84 DB System as Enabler / 86 Pivotal Role of the Database System / 87 Data Storage / 87 Information Delivery / 88 Foundation for Applications / 89 Indispensable for Modern Enterprise / 90 Chapter Summary / 91 Review Questions / 91 Exercises / 92 4 DATABASE DEVELOPMENT LIFE CYCLE 93 Chapter Objectives / 93 Major Development Steps / 94 Starting the Process / 94 Design and Development / 96 Development and Implementation / 98 CONTENTS ix
- 12. Steps and Tasks / 98 Roles and Responsibilities / 99 Management and Control / 101 Planning for the DB System / 103 Scope of Overall Planning / 104 Who Does the Planning? / 105 Impact of the Business Plan / 105 The Database Plan / 107 Critical Planning Issues / 108 Feasibility Study / 109 Purpose and Extent / 109 Technological Infrastructure / 111 Skills Review / 112 Estimation of Costs / 113 Assessment of Benefits / 115 Weighing the Options / 117 Requirements Definition / 118 Requirements Gathering Methods / 119 Conducting User Interviews / 120 Observation of Processes / 124 Review of Applications / 125 Study of Documents / 126 Consolidating Information Requirements / 126 Requirements Definition Document / 127 The Design Phase / 128 Design Objectives / 129 Logical Versus Physical Design / 129 The External Schema / 130 The Conceptual Schema / 130 The Internal Schema / 131 Implementation and Deployment / 132 Conceptual to Internal Schema / 133 DBMS Installation / 134 Building the Data Dictionary / 134 Populating the Databases / 135 Developing Application Interfaces / 135 Maintenance and Growth / 135 Administration Tools / 136 Ongoing Monitoring / 137 Performance Tuning / 137 Managing Growth / 138 Chapter Summary / 139 x CONTENTS
- 13. Review Questions / 139 Exercises / 140 PART III CONCEPTUAL DATA MODELING 141 5 DATA MODELING BASICS 143 Chapter Objectives / 143 What is a Data Model? / 144 Why Create a Data Model? / 144 Real-World Information Requirements / 145 Data Model as the Replica / 146 Data Model Components / 147 Data Modeling Concepts / 148 Representation of Information Requirements / 149 Filtering Out Irrelevant Data / 150 Mapping of Components / 151 Data Model to Data Design / 151 Patterns of Data Modeling / 153 High-Level Data Model / 154 Object-Based Modeling Technique / 154 Entity-Relationship Modeling Technique / 155 Data Modeling Aids / 156 Data Views / 156 What are Data Views? / 157 Collection of Information Requirements / 157 Windows into the Data System / 158 Data Views: Two Perceptions / 159 View Integration / 160 Merging Individual User Views / 160 Integrating Partial Data Models / 162 Enhancement and Validation / 162 Consolidated Data Model / 163 Chapter Summary / 164 Review Questions / 165 Exercises / 165 6 OBJECT-BASED DATA MODEL: PRINCIPLES AND COMPONENTS 167 Chapter Objectives / 167 Overview of Object-Based Modeling / 168 CONTENTS xi
- 14. A Generic Data Model / 168 Benefits of Object-Based Data Model / 169 Introduction to Components / 169 Mapping of Real-World Information / 171 Example of a Model Diagram / 174 Business Objects / 177 Object Sets and Instances / 177 Types of Objects / 178 Recognizing Object Sets / 178 Attributes / 179 Identifiers for Instances / 182 Relationships between Objects / 183 Role of Relationships / 183 Cardinality in Relationships / 184 Aggregate Objects / 189 Degrees of Relationships / 192 Generalization and Specialization / 192 Supersets and Subsets / 194 Generalization Hierarchy / 194 Inheritance of Attributes / 196 Inheritance of Relationships / 196 Special Cases / 197 Special Object Types and Relationships / 199 Conceptual and Physical Objects / 200 Recursive Relationships / 201 Assembly Structures / 202 Review of Object-Based Data Model / 203 Summary of Components / 203 Comprehensive Data Model Diagram / 203 Chapter Summary / 203 Review Questions / 204 Exercises / 205 7 ENTITY-RELATIONSHIP DATA MODEL 206 Chapter Objectives / 206 Introduction to E-R Model / 207 Basic Concepts / 207 Data Modeling Process / 208 Major Components / 209 Entities / 210 Entity Definition / 211 xii CONTENTS
- 15. Entity Types / 211 Entity Sets / 212 Weak Entity Types / 212 Attributes / 214 Attribute Specification / 214 Values and Domains / 215 Attribute Types / 215 Candidate and Primary Keys / 218 Relationships / 219 Association Between Entities / 219 Degree of a Relationship / 221 Cardinality in Relationships / 221 Optional and Mandatory Conditions / 221 Special Cases / 226 Modeling Time-Dependent Components / 226 Identifying and Nonidentifying Relationships / 226 Attributes of Relationship Types / 228 When to Use a Gerund / 228 Generalization and Specialization / 229 The Entity-Relationship Diagram (ERD) / 230 Review of Components and Notations / 230 Sample ERD / 231 Highlights of Sample ERD / 232 Chapter Summary / 233 Review Questions / 234 Exercises / 234 PART IV THE RELATIONAL DATA MODEL 237 8 RELATIONAL DATA MODEL FUNDAMENTALS 239 Chapter Objectives / 239 Structure and Components / 240 Strength of the Relational Model / 240 Relation: The Single Modeling Concept / 241 Columns as Attributes / 242 Rows as Instances / 242 Primary Key / 243 Relationship Through Foreign Keys / 244 Relational Model Notation / 245 Data Integrity Constraints / 246 CONTENTS xiii
- 16. Why Data Integrity? / 247 Basic Relational Properties / 247 Entity Integrity / 248 Referential Integrity / 249 Functional Dependencies / 250 Data Manipulation / 251 Role of Data Languages / 252 Data Manipulation Languages / 252 Relational Algebra / 253 Relational Calculus / 262 Comparison of Generic Languages / 264 Relational Model Design / 266 Requirements to Data Model / 267 Design Approaches / 267 Semantic to Relational Model / 267 Traditional Method / 268 Evaluation of the Two Methods / 269 Chapter Summary / 270 Review Questions / 271 Exercises / 271 9 SEMANTIC DATA MODEL TO RELATIONAL DATA MODEL 273 Chapter Objectives / 273 Model Transformation Approach / 274 Merits / 274 When to Use This Method / 276 Steps and Tasks / 277 Critical Issues / 277 Mapping of Components / 278 Mapping and Transformation / 279 Object Sets to Relations / 279 Attributes / 280 Instance Identifiers / 281 Transformation of Relationships / 282 One-to-One Relationships / 282 One-to-Many Relationships / 284 Many-to-Many Relationships / 286 Mandatory and Optional Conditions / 291 Aggregate Objects as Relationships / 296 Identifying Relationship / 296 Supersets and Subsets / 297 xiv CONTENTS
- 17. Outcome of Model Transformation / 297 Comparison of Models / 298 Summary of Transformation / 299 Chapter Summary / 299 Review Questions / 300 Exercises / 301 10 DATA NORMALIZATION METHOD 303 Chapter Objectives / 303 Informal Design / 304 Forming Relations from Requirements / 304 Pitfalls of Informal Design / 304 Update Anomaly / 307 Deletion Anomaly / 307 Addition Anomaly / 308 Normalization Approach / 308 Purpose and Merits / 309 How to Apply This Method / 309 Steps and Tasks / 310 Fundamental Normal Forms / 311 First Normal Form / 311 Second Normal Form / 312 Third Normal Form / 314 Boyce-Codd Normal Form / 317 Higher Normal Forms / 317 Fourth Normal Form / 319 Fifth Normal Form / 320 Domain-Key Normal Form / 321 Normalization Summary / 322 Review of the Steps / 323 Critical Issues / 324 Normalization Example / 325 Chapter Summary / 326 Review Questions / 327 Exercises / 328 PART V DESIGN AND IMPLEMENTATION 331 11 COMPLETING THE LOGICAL DESIGN 333 Chapter Objectives / 333 Significance of Logical Design / 334 CONTENTS xv
- 18. Logical Structure Versus Physical Structure / 334 Logical Design Phase in DDLC / 335 Why This Phase Is Necessary / 335 Input to Physical Design / 337 Ensuring Design Completeness / 337 Data Modeling in Logical Design / 339 Steps for Completing Logical Design / 339 Representing Entities / 340 Representing Attributes / 340 Representing Relationships / 340 Rules and Constraints / 342 Design for the Relational Data Model / 342 Relation as the Single Design Concept / 343 Logical Design Components / 344 Logical Schema / 344 Special Considerations / 345 Documentation of Logical Design / 346 Logical Design Outputs / 346 Usage of Outputs / 347 Use of CASE Tools / 347 Documentation Outline / 348 Chapter Summary / 349 Review Questions / 349 Exercises / 350 12 THE PHYSICAL DESIGN PROCESS 351 Chapter Objectives / 351 Introduction to Physical Design / 352 Logical to Physical Design / 352 Goals and Design Decisions / 354 Physical Design Components / 355 Physical Design Tasks / 356 Use of Data Dictionary / 356 Data Storage and Access / 358 Storage Management / 359 Access of Physical Data / 360 Files, Blocks, and Records / 360 File Organization / 363 Linking of Related Data Elements / 366 RAID Technology Basics / 367 xvi CONTENTS
- 19. Indexing Techniques / 371 Primary Indexes / 372 Binary Search / 373 B-Tree Index / 374 Secondary Indexes / 375 Bitmapped Indexing / 376 Other Performance Considerations / 377 Clustering / 378 Denormalization / 379 Fragmentation / 380 Memory Buffer Management / 380 Preconstructed Joins / 381 Chapter Summary / 382 Review Questions / 383 Exercises / 383 13 SPECIAL IMPLEMENTATION CONSIDERATIONS 385 Chapter Objectives / 385 Implementation Languages / 386 Meaning of Model Implementation / 386 Role of Languages / 387 Languages for the Relational Model / 389 SQL: The Relational Standard / 391 Overall Features / 392 Brief History and Evolution / 393 Data Definition in SQL / 394 Data Retrieval in SQL / 397 Data Maintenance in SQL / 399 Data Control in SQL / 401 Queries / 403 Summary of SQL Query Components / 406 Database Access from Application Program / 406 Query Processing / 407 Query Processing Steps / 409 The Query Optimizer / 410 Heuristic Approach / 411 Cost-Based Optimization / 412 Database System Deployment / 415 Deployment Tasks / 416 Implementation in Centralized Architecture / 417 Implementation in Client/Server Architecture / 418 CONTENTS xvii
- 20. Chapter Summary / 420 Review Questions / 420 Exercises / 421 PART VI DATABASE ADMINISTRATION AND MAINTENANCE 423 14 OVERVIEW OF ADMINISTRATION FUNCTIONS 425 Chapter Objectives / 425 Significance of Administration / 426 Essential Need for Administration / 427 Administration Objectives / 430 Data Administration / 432 Database Administration / 432 Skills and Responsibilities / 433 Administrative Roles / 433 Areas of Responsibility / 434 Skills, Knowledge, and Experience / 436 Interaction with Users and Practitioners / 437 During Development / 437 Planning and Feasibility Study / 438 Requirements Definition / 439 Logical Design / 439 Physical Design / 440 Implementation and Deployment / 440 After Deployment / 441 Ongoing Functions / 441 Maintenance of Service Levels / 442 Enhancements to Database System / 442 Growth and Change / 442 Chapter Summary / 443 Review Questions / 444 Exercises / 444 15 DATA INTEGRITY 446 Chapter Objectives / 446 Transaction Processing / 447 Transaction Concepts / 447 Properties of Transactions / 449 Transaction States / 451 xviii CONTENTS
- 21. Processing of Transactions / 452 Integrity Considerations / 454 Concurrent Transactions / 456 Motivation for Concurrency / 458 Concurrency Problems / 458 Transactions and Schedules / 460 Serializability / 462 Recoverability / 465 Concurrency Control / 466 Lock-Based Resolution / 467 Application of Lock-Based Techniques / 470 Deadlock: Prevention and Detection / 473 Timestamp-Based Resolution / 476 Optimistic Techniques / 479 Database Failures and Recovery / 481 Classification of Failures / 481 Recovery Concepts / 482 Logging / 483 Checkpoint / 485 Log-Based Recovery Techniques / 486 Shadow Paging / 489 A Recovery Example / 491 Chapter Summary / 491 Review Questions / 493 Exercises / 493 16 DATABASE SECURITY 495 Chapter Objectives / 495 Security Issues / 496 Goals and Objectives / 496 Security Problems / 497 Solution Options / 499 Privacy Issues / 500 Web Security / 501 Access Control / 501 Levels and Types of Data Access / 502 Discretionary Control / 503 Use of Views / 506 SQL Examples / 507 Mandatory Control / 508 Special Security Considerations / 510 CONTENTS xix
- 22. Authorization / 510 Authentication / 512 Role of the DBA / 513 Statistical Databases / 513 Encryption / 516 What is Encryption? / 516 Encryption Methods / 518 Data Encryption Standard / 519 Public Key Encryption / 520 Chapter Summary / 523 Review Questions / 523 Exercises / 524 17 ONGOING MAINTENANCE AND GROWTH 525 Chapter Objectives / 525 Routine Maintenance / 527 Backup and Recovery / 527 Security Maintenance / 529 Space Management / 531 Concurrency Control / 532 Problem Resolution / 532 Monitoring and Review / 533 Purpose of Monitoring / 534 The Monitoring Process / 534 Gathering of Statistics / 536 Review of Operations / 536 Use of Benchmarks / 537 Growth and Enhancements / 538 Ongoing Growth and Enhancements / 538 Application Enhancements / 539 Schema Revisions / 541 DBMS Version Upgrades / 542 Tuning for Performance / 543 Goals and Solution Options / 544 Tuning Indexes / 545 Tuning Queries and Transactions / 546 Tuning the Schema / 547 Chapter Summary / 547 Review Questions / 548 Exercises / 549 xx CONTENTS
- 23. PART VII ADVANCED DATABASE TOPICS 551 18 DISTRIBUTED DATABASE SYSTEMS 553 Chapter Objectives / 553 Fundamental Principles / 554 What is a Distributed Database? / 555 Basic Concepts / 556 Motivation and Goals / 557 Advantages and Disadvantages / 557 Distributed Databases / 559 Types and Configurations / 559 DDBMS / 561 Network Component / 566 Data Distribution / 568 Architectural Options / 572 Design and Implementation Issues / 574 Transparencies / 576 Transparency: Key Ideal / 576 Fragmentation Transparency / 577 Replication Transparency / 578 Location Transparency / 578 Network Transparency / 578 Naming Transparency / 579 Failure Transparency / 579 Distributed Processing / 579 Query Processing / 580 Transaction Processing / 585 Concurrency Control / 588 Distributed Recovery / 592 Chapter Summary / 595 Review Questions / 596 Exercises / 596 19 DATABASE SYSTEMS AND THE WEB 598 Chapter Objectives / 598 Web Technology: A Refresher / 599 The Internet and the Web / 599 HyperText Transfer Protocol (HTTP) / 601 Uniform Resource Locator (URL) / 602 CONTENTS xxi
- 24. HyperText Markup Language (HTML) / 603 Beyond HTML / 605 Intranets and Extranets / 606 Web-Database Integration / 607 Motivation for Integration / 608 Requisites for Integration / 609 Architecture for Integration / 609 Advantages and Disadvantages / 611 Integration Approaches / 613 Common Gateway Interface (CGI) / 613 Application Programming Interface (API) / 616 Server-Side Includes (SSI) / 618 Cookies / 619 Use of Java Applications / 620 Use of Scripting Languages / 622 Database Tools / 623 Security Options / 625 Significance of Protection / 625 Firewalls, Wrappers, and Proxies / 626 Digital Signatures and Digital Certificates / 628 SET and SST / 629 SSL and S-HTTP / 630 Java Security / 630 Chapter Summary / 633 Review Questions / 634 Exercises / 634 20 TRENDS IN DATABASE TECHNOLOGY 636 Chapter Objectives / 636 Object-Oriented Databases / 637 Basic Concepts / 638 Objects and Classes / 640 Methods and Messages / 641 Inheritance / 643 Polymorphism / 643 Object-Oriented Data Model / 644 Object-Relational Databases / 646 The Driving Forces / 647 What is an ORDBMS? / 648 Feature Highlights / 648 SQL-3: Object-Relational Support / 649 xxii CONTENTS
- 25. Databases for Decision Support / 649 Data Warehousing / 650 Online Analytical Processing (OLAP) / 661 Data Mining / 667 Leading Trends: Basic Overview / 671 Parallel Databases / 672 Active Databases / 674 Intelligent Databases / 675 Deductive Databases / 676 Multimedia Databases / 676 Mobile Databases / 678 Geographic Databases / 681 Chapter Summary / 683 Review Questions / 683 Exercises / 684 APPENDICES 685 A Legacy System Models: Hierarchical and Network 687 B Codd’s Relational Rules 692 C Diagramming Conventions and Symbols 694 D Use of CASE tools 700 E Review of major commercial DBMSs 703 F Database Design and Development Summary 712 References 716 Glossary 718 Index 729 CONTENTS xxiii
- 26. PREFACE Are you a programmer, systems analyst, network specialist, project leader, or any other type of information technology professional? Alternatively, are you a student aspiring for a career in information technology? Then you definitely need to know how database systems are designed and developed. You have to understand the fun- damentals of database systems clearly. As you know, in today’s business environment, companies depend on their data- bases to provide crucial information essential for running their businesses. Gone are the days of file-oriented data systems. Now database systems form the center- piece of the growing and maturing electronic commerce. Database and Web tech- nologies have merged. Over the years, commercial database products have become sophisticated and robust. In this transformed computing environment, knowledge of database systems can no longer be confined only to specialists such as data analysts and database admin- istrators. All IT professionals need basic knowledge of database technology and its applications. This book comes to you as an essential guide on database design and development, covering all the necessary topics in proper measure, written especially for IT professionals—present and future. THE SCENARIO In every industry across the board, from retail chain stores to financial institutions, from manufacturing organizations to government departments, and from airline companies to utility businesses, database systems have become the norm for in- formation storage and retrieval. Whether it is a Web-based application driving electronic commerce or an inventory control application managing just-in-time inventory or a data warehouse system supporting strategic decision making, you need an effective and successful technology to store and retrieve data. It is no xxv
- 27. wonder that companies have adopted database technology without reservations. The modern relational database system, proven to be eminently suitable for data management, has become more and more pervasive. Over the recent years, vendors of all leading database products have released more sophisticated and powerful software versions. Database manage- ment systems such as DB2, Informix, Oracle, SQL Server, and Sybase have all expanded with several useful features. Database management systems have become the centerpiece of e-business. Numerous books feature commercial database products. THE ROLE OF IT In this scenario, the information technology department of every organization has a primary responsibility. The department has to support and keep the database systems running. Without the database system, the day-to-day business of the orga- nization will come to a grinding halt. Therefore, all IT staff must understand the workings of database systems. It is not enough to have just a handful of specialists knowledgeable in database tech- nology. All applications in the enterprise now work with databases. Every IT pro- fessional, therefore, must know the basics of the technology. Everyone must learn how database systems are designed and developed. Every IT professional must understand the fundamental principles. WHAT THIS BOOK CAN DO FOR YOU This book provides you with necessary information on the basics of database tech- nology. It covers all the essential topics carefully with proper emphasis as required by each topic. If you are new to the fundamentals of database technology, this book is an essential pre-requisite before you determine the next steps toward specializa- tion in the database field. If you are already familiar with the technology, this book is a suitable refresher to reinforce your grasp of the subject. More specifically, here is a summary of what this book can do for you: Specially designed for IT professionals Specifically intended for IT professionals like you, this book builds on what you already know. The book takes into account the background, knowledge, and terminology of IT professionals; it presents the topics in a suitable direct style. Comprehensive with just the necessary details The book deals with every significant topic needed by IT professionals looking for the fundamentals. It encompasses database concepts, terminology, planning, implementation, and administration; the book also includes significant technol- ogy trends. xxvi PREFACE
- 28. Suitably organized The book follows an organization most apt and logical for IT professionals con- centrating on the fundamentals. It is the type of organization these professionals is most familiar in their day-to-day work experience. Beginning with an overview of basic concepts, the book moves on to an overview of the database system development process, then to the important topic of data modeling, on to design, then to implementation, and concludes with ongoing maintenance and growth. Feature highlights Every chapter opens up with chapter objectives and concludes with a chapter summary. At the end of each chapter, you find a set of review questions and exer- cises. These features make the book eminently suitable for self-study or for use as a textbook in a college course. Exposure to real-world situations Throughout the book, each concept or technique is illustrated with real-world examples. An appendix is devoted to the review of leading commercial database management systems. Preparation for database specialists Although intended as a first course on the fundamentals, the book provides suf- ficient coverage of each topic so that you may easily proceed to the next phase of specialization for specific roles such as data modeler, database designer, data analyst, data administrator, or database administrator. ACKNOWLEDGMENTS The authors listed in the reference section at the end of the book greatly enhanced my understanding and appreciation for database technology. I am deeply indebted to the authors for their insights and observations;I wish to express my sincere thanks to them. I must also record my appreciation for the several professional colleagues who had worked with me on various database projects during my 25-year consulting career. Also, thanks are due to the many students in my database classes over the years. Interactions with my students and colleagues have enabled me to shape this book according to the specific needs of IT professionals. PAULRAJ PONNIAH, Ph.D. Milltown, New Jersey November 2002 PREFACE xxvii
- 29. PART I BASIC DATABASE CONCEPTS
- 30. CHAPTER 1 THE DATABASE APPROACH CHAPTER OBJECTIVES • Understand how the database approach is different and superior to earlier data systems • Examine how information demand and technology explosion drive database systems • Trace the evolution of data systems and note how we have arrived at the database approach • Comprehend the benefits of database systems and perceive the need for them • Survey briefly various data models, types of databases, and the database industry Consider the following scenarios: • You meet someone in a computer store. As a knowledgeable IT professional, you want to help this person. He says he is looking for database software to keep the names and addresses of his customers to do his mailings and billings. But what he really needs is a mail-merge program. • You call your travel agent to make your airline reservations for the vacation you have been waiting for all year.The agent responds by saying that she cannot do that just now because the database is down. She really means that the reser- vations computer system is not working. • Here is one more. You call your cellular phone company to complain about errors on the latest billing statement. The phone company representative says Database Design and Development: An Essential Guide for IT Professionals by Paulraj Ponniah ISBN 0-471-21877-4 Copyright © 2003 by John Wiley and Sons, Inc. 3
- 31. that the database must have printed some incorrect numbers. What the repre- sentative really implies is that the billing application has miscalculated the charges. In our modern society most people know the term database without under- standing its full and clear meaning. Even in information technology circles, not everyone knows the concepts in reasonable detail. What is a database? Is it data? Is it software? Is it the place where you store data? Is there something special about the way you store data? Is it how you store and retrieve data? What exactly is a database system? What are the features and functions? Many more such questions arise. Today, almost all organizations depend on their database systems for the crucial information they need to run their business. In every industry across the board, from retail chain stores to financial institutions, from manufacturing enterprises to gov- ernment departments, and from airline companies to utility businesses, database systems have become the norm for information storage and retrieval. Database systems form the centerpiece of the growing and maturing electronic commerce. Database and Web technologies have merged. The Information Technology department of today’s organization has a primary responsibility: The department has to support and keep the database systems running. In this transformed computing environment, knowledge of database systems is no longer confined only to specialists such as data analysts and database administrators. Are you are a systems analyst, programmer, project leader, or network specialist? Then you also need to know the basics of database systems. You also need to grasp the significance of the database approach. All IT profes- sionals need to study the basic principles and techniques of database design and development. First, let us begin to understand how we got to this stage where most organiza- tions depend on their database systems for running the business. Let us trace the evolution of data systems and see the essential need for the database approach. Let us understand what exactly the database approach is. Let us briefly survey the database industry and grasp the significance of the developments. EVOLUTION OF DATA SYSTEMS How were companies running their business before computers came into use? Even at that time, organizations needed information to execute the business processes, sell goods and services, and satisfy the needs of customers. Manual files supported business operations. Accounting personnel performed manual calculations and pre- pared invoices. Payroll departments manually wrote the checks. Business operations were reasonably satisfactory. So, what happened? How did we get to the computer database systems of today? When computers were introduced in the 1960s, computer file systems replaced the manual files. This marked a significant leap in the way data was stored and retrieved for business operations. What has been really happening from that time until now, when database systems have become the norm? What prompted the progress toward database systems? 4 THE DATABASE APPROACH
- 32. From the 1970s onward, two striking and remarkable phenomena were distinctly observed. Refer to Figure 1-1 indicating these two major developments. First, demand for information has escalated in every organization. Organizations have steadily become global and widespread. Organizations have to contend with fierce competitive pressures. They need vast and complex information to stay in business and make a profit. Second, the past three decades have witnessed a huge, explosive growth in information technology. Processors have become faster, cheaper, and smaller. Operating systems have become powerful and robust. Data storage media have expanded tremendously in capacity; data storage prices have tumbled. Network and communication technology can now connect any remote site without difficulty. Application programming and people-machine interface have dramatically improved. The escalating demand for information and the explosive growth in information technology have worked hand in hand to bring about the evolution to database systems. Ever-increasing demand for information drives the need for better methods of storing and retrieving data, for faster ways of processing data, and for improved methods of providing information. The demand for more and better information drove the technology growth. Progress in technology, in turn, spurred the capabil- ity to provide different types of information, not just to run day-to-day operations of an organization, but also to make strategic decisions. Let us first examine the pertinent aspects of the technology explosion as related to data systems, because these are what we are specifically interested in. Then let us discuss the escalating demand for information that has prompted better and improved data systems. Technology Explosion If you have been in the information technology area for 5–10 years, you are cer- tainly an eyewitness to the explosive growth. Growth is not confined to any one EVOLUTION OF DATA SYSTEMS 5 1960 2010 Data Systems Computing Technology Demand for Information GROWTH TIME Figure 1-1 Technology growth and demand for information.
- 33. sector. All aspects of the technology have been improving tremendously. Here are some specifics: • Twenty-five years ago, there were only 50,000 computers in the whole world; now more than 500,000 are installed every day. • More than 60% of American households have at least one computer; more than 50% have e-mail and Internet access. • Growth of the Internet and the use of the Web have overshadowed the PC breakthrough of the 1970s; at the beginning of 2000, about 50 million house- holds worldwide were estimated to be using the Internet; by the end of 2005, this number is expected to grow 10-fold. • About 7 years ago, there were only 50 websites; now 100,000 are added every hour. • Databases in the terabyte range are becoming common; a few years ago, even the gigabyte range was unusual. • In the mid-1960s,programmers in large corporations had to write programs that had to run on 12K machines; today even your personal computer at home has 10,000 times larger memory. Growth has not been isolated here and there in hardware and software.We notice explosive growth in all sectors of information technology. Let us proceed further to look at specific areas of information technology that are related to data systems. Data Storage Devices Have you seen an 80-column card that very early com- puter systems used to store data? Each column in a card had holes punched to represent a single character. So a card could hold up to 80 characters. Keypunch operators typed data and program code into the cards. In the next stage, computer systems stored data on magnetic tapes. Initially, magnetic tapes of 800 BPI (bytes per inch) were used. Then we moved on to higher densities of 1600 BPI and 6250 BPI. For a brief while, paper tapes with punched holes were used as the storage medium. Special-purpose paper tape readers were used to read data from paper tapes. It was a large leap forward when disk drives began to replace the earlier data storage media. Disk drives in mainframes consist of sets of large circular disks arranged in parallel with a common spindle. Sophisticated disk drives have come to stay as the common storage device of choice.Today’s data servers use RAID (redun- dant array of inexpensive disks) technology as the advanced fault-tolerant storage system. Data storage devices have progressed tremendously from the primitive punched cards to the sophisticated RAID systems. Three-and-a-Half-Inch Disk Drives You are very familiar with the three-and-a- half-inch disk drives in your home computer system. Just review the progress in the capacities of these disk drives. See how the capacities kept doubling every year. Note the following details: 1992 1 gigabyte 1993 2 gigabytes 6 THE DATABASE APPROACH
- 34. 1994 4 gigabytes 1995 9 gigabytes 1997 18 gigabytes 2000 50 gigabytes Computer Applications Over the years, the types of computer applications have changed and progressed from mere bookkeeping applications to multimedia and data mining applications. Some of you might remember the days when the com- puter department was known as the data processing department. Applications in those days just processed data in elementary ways to produce some reports. The technology explosion resulted in a grand transition of computer usage from simple to increasing sophistication. Review the following details. Data Processing Applications (DP). In the early days of computing, computer departments built applications just to replace clerical labor. Mostly, these applica- tions performed simple accounting and financial functions. These applications pro- duced straightforward reports. Speed and accuracy of the computer in performing calculations were the primary factors. Computer systems stored and retrieved data from magnetic tapes and earlier versions of disk drives. Applications used sequen- tial or flat files to organize data. Management Information Systems (MIS). In the next stage, growth of technology manifested itself in applications that went beyond accounting and finance to sup- porting the entire core business of an organization. Applications began to appear to process orders, manage inventory, bill customers, pay employees, and so on. Orga- nizations depended on their management information systems for their day-to-day business. Storage and retrieval of data mostly depended on hard disks. Many appli- cations adopted the use of database technology. Decision-Support Systems (DSS). Further technology growth in processor speed, storage media, systems software, and database techniques pushed the application types to systems that supported strategic decision making. These applications are not meant for supporting day-to-day operations of a business but for providing information to executives and managers to make strategic decisions. In which markets should the company expand? Where should the next distribution ware- house be built? Which product lines should be discontinued? Which ones should be boosted? These applications dealt with sales analysis, profitability analysis, and cus- tomer support. Decision-support systems made use of improved storage facilities and newer features of database technology. Data Warehousing (DW) and Data Mining (DM) Systems. In recent years, with the enormous progress in processor scalability, mass storage, and database methods, organizations are able to forge ahead with their applications, especially in building data warehousing and data mining systems. These recent decision-support systems, much more sophisticated than earlier attempts, require large volumes of data and complex analytical techniques. These systems need large databases specially designed and built separately from the databases that support the day-to-day oper- ational systems. EVOLUTION OF DATA SYSTEMS 7
- 35. Data Systems What is the effect of the technology explosion on the way data is organized? Over the years, how were businesses organizing data? We just looked at the way applications have progressed from simpler types toward increasing sophis- tication. What about data systems? Manual-Type Records. Very early computer applications worked with data stored on punched cards and paper tapes. Keypunch operators prepared data on these primitive media from manual files and records. Computer applications read data from cards and tapes to prepare reports. Sequential Files. Improved storage media such as magnetic tapes and early disk drives enabled application developers to organize data as sequential (or flat) files. Each file contained data records of the same type arranged sequentially one after the other, usually in the order in which they were created. Sorting techniques allowed data records to be resorted in a different sequence. Databases. Increased sophistication in data storage techniques on hard disk drives and enhancements to operating systems enabled random and quick access of data. Data systems moved to a wholly new level. Applications were able to store data in databases and retrieve data sequentially and randomly. Demand for Information Of the two major factors that mutually contributed to the database approach to computing, so far we have considered the explosive growth of technology. Let us now turn our attention to the other factor, namely, the escalating demand for infor- mation. It is not just more information that organizations need. The demand for information includes several dimensions. Consider how billing requirements and sales analysis have changed. In the early years of computing, organizations were happy if they could bill their customers once a month and review total sales by product quarterly. Now it is completely different. Organizations must bill every sale right away to keep up the cash flow. They need up-to-date customer balance and daily and cumulative sales totals by products.What about inventory reconciliation? Earlier systems provided reports to reconcile inven- tory or to determine profitability only at the end of each month. Now organizations need daily inventory reconciliation to manage inventory better, daily profitability analysis to plan sales campaigns, and daily customer information to improve cus- tomer service. In the earlier period of computing, organizations were satisfied with information showing only current activity. They could use the information to manage day-to-day business and make operational decisions. In the changed business climate of globalization and fierce competition, this type of information alone is no longer adequate. Companies need information to plan and shape their future. They need information, not just to run day-to-day operations, but to make strategic decisions as well. What about the delivery of information now compared to the early days of com- puting? Today, online information is the norm for most companies. Fast response times and access to large volumes of data have become essential. Earlier computer 8 THE DATABASE APPROACH
- 36. systems just provided reports, mostly once a month, a few once a week, and a small number once a day. Organizations have come to realize that information is a key asset to be care- fully managed and used for greater profitability. In summary, demand for informa- tion by today’s enterprises contains the following attributes: • More information • Newer purposes • Different information types • Integrated information • Information to be shared • Faster access to information Waves of Evolution As we have seen so far, information technology, along with and because of the esca- lating demand for information, has made giant strides in the past few decades. Evo- lution to higher levels is evident in every aspect of information technology. The evolution has taken place in distinct waves. Refer to Figure 1-2. Note carefully the evolution of information technology in the three major areas. First note how the very methods of computing technology have progressed from mainframes to client/server architecture. The centrally administered mainframes have made room for the client/server configuration in which each set of machines can perform specialized tasks. What about the way in which humans interface with computers? In earlier days, we punched data on cards and fed them to be read by the early computers. Then came the CRTs (cathode-ray terminals) where textual data could be typed into the computer through the use of keyboards. Point-and-click GUIs (graphical user inter- faces) proved to be a major improvement. Now, interfacing with computers through EVOLUTION OF DATA SYSTEMS 9 1950 1960 1970 1980 1990 2000 Computing Technology Processing Options Human/Machine Interface Mainframe Mini PCs/Networking Client/Server Punch Card GUI Voice Video Display Batch Online Networked Figure 1-2 Information technology: waves of evolution.
- 37. the human voice is gaining ground. What a major transition from punch cards to direct voice input! In the early days of computing, transactions were batched together for process- ing at the end of a stipulated period. For example, you could not invoice each sale as it happened. You had to collect and batch all the sales for a month and run the batched sales through the invoicing application. We moved to online transaction processing in the next wave. Now transactions are transmitted and processed over LANs (local area networks) and WANs (wide area networks). File-Oriented Data Systems As the demand for information continued to increase, organizations began to adopt improved file systems to store and access data. The file-oriented data systems essen- tially mimicked the manual file systems. The computer files corresponded to the paper files. In a filing cabinet, you store file folders and each file folder contains file records. Similarly, the computer systems use electronic files containing records. For example, a customer file would contain records, with each record containing data about a single customer. In the beginning, these computer files were primarily used for accounting applications. As we shall discuss in some detail, file-oriented systems have serious limitations. Therefore, organizations needed to go to better and improved methods for data storage and access. File-oriented systems started out by using sequential or flat files. When you need to retrieve the 100th record from a sequential file, you have to read and bypass the first 99 records before you can get to record number 100. This is a very serious shortcoming. Therefore, slightly better methods of retrieval evolved. This was the transition to improved file-oriented data systems. Let us review how storage and retrieval methods apply to a customer file. Sequential File. Customer records are stored in the sequence in which they are entered into the file. Record retrieval is sequential. For the file to be processed in any other sequence, it must be sorted in the required sequence. ISAM File. This is the indexed-sequential access method. The customer records in the data file are stored sequentially, similar to the sequential file method. However, another index file is created, for example, with the customer numbers and the phys- ical addresses of the records. When the record of a specific customer is needed, as done previously, you do not have to read the records of the data file one after the other until you find the record you are looking for. You can read the smaller index file, find the record you are looking for, and then use the physical address of the data record stored in the index file. VSAM File. This is based on virtual storage access method, a major improvement over ISAM files. VSAM files provide for indexed access. Also, this method provides for storing and retrieving records directly from the customer file without an index file. In the direct method, the address where a customer record is stored may be cal- culated from the customer number with a specialized algorithm. 10 THE DATABASE APPROACH
- 38. WHY DATABASE SYSTEMS? We traced the evolution of data systems. We grasped the essentials of the explosive growth of information technology. We noted the escalating demand of organizations for information. We observed how growth in information technology and the increased demand for information worked hand in hand. Increasing demand for information spurred the growth of information technology. Growth of informa- tion technology, in turn, enabled organizations to satisfy the increasing demand for information. Let us summarize the driving forces for organizations to adopt database systems. A major reason is the inadequacy of the earlier file-oriented data systems. We shall review the limitations and see how database systems overcome the limitations and provide significant benefits. The Driving Forces Among others, four major forces drove organizations to adopt database systems. Figure 1-3 illustrates these four major forces. Information as a Corporate Asset. Today, companies strongly realize that infor- mation is a corporate asset similar to other assets such as cash, plant and equip- ment, or inventory. Proper management of key assets is essential for success. Companies understand that it is essential to manage information as a key asset. They understand the need to find improved methods for storing, retrieving, and using information. Explosive Growth of Computer Technology. Computer technology, especially data storage and retrieval systems, has grown in a phenomenal manner. Without growth in this sector, it is unlikely that we could have progressed to database systems that need sophisticated ways of data storage and retrieval. Escalating Demand for Information. We have noted the increase in demand for information by organizations, not only in volume but in the types of information as WHY DATABASE SYSTEMS? 11 Database Systems Information as corporate asset Explosive growth of computer technology Escalating demand for information Inadequacy of earlier data systems Figure 1-3 Database systems: the driving forces.
- 39. well. If companies did not need more and newer types of information, there would have been no impetus for development of database systems.The earlier data systems might have been satisfactory. Inadequacy of Earlier Data Systems. Suppose the earlier data systems were able to meet the escalating demand for information. Then why bother to find better methods? But the fact is that these earlier systems were grossly inadequate to meet the information demands. Storage and management of large volumes of data were not adequate. Finding and retrieving information were extremely difficult. Protect- ing the information asset of a company was nearly impossible with the earlier data systems. Why was this so? How were the earlier systems inadequate? In what ways could they not meet the information demands? Understanding the limitations will give you a better appreciation for database systems. Inadequacy of Earlier Data Systems Assume that you work for a company called Progressive Book Distributors in the early 1970s. Your company purchases books from various publishers and sells them to retail bookstores and book clubs. The computer applications in your company would work with sequential files because those are the types of data systems available at that time. Here is a list of possible sequential computer files in your company. Customer master file Every time a new customer comes on board, a record is created in the file, with a new customer number, in the order in which the cus- tomers are added. Book master file As each new book is added to the inventory, a record is created in the file, with ISBN identifying each book. Salesperson file As each new salesperson is hired, the person is given an iden- tification number and data about him or her is added to the file. Sale transaction file Each sale is recorded with the date of the sale. Publisher file As each new publisher is included, a record is created in the file, with a new publisher number, in the order in which the publishers are added. Payment transaction file Payments received from customers are recorded with the date of the payment. Refer to Figure 1-4 showing the fields and sample data for each file. What types of information is your company’s staff looking for? Do they need to print an invoice for customer Allbooks Book Store for the sale on January 10, 2002? Do they want the total sales of all books from publishers Ron Fairchild during the month of December 2001? Do they want a list of all customers in New York state? In today’s computing environment, no one will think of these requests as difficult or impossible. This was not the case with file-oriented applications of the early 1970s. File-oriented data systems have serious limitations. Let us take just one specific example of printing statements to customers for sales. This had to be done in a batch mode at the end of a reasonable interval such as at 12 THE DATABASE APPROACH
- 40. the end of a month. All the sales transactions and payment transactions for the month had to be batched together and processed in a batch mode. Figure 1-5 indicates a flowchart of the jobs that must be run to produce the billing statements. Even an initial review of the flowchart reveals that there are too many sorts for just producing simple billing statements. That is because each file is kept in a sequence that is not useful for the processing logic of the entire application. The whole concept of batch processing is very inflexible. Suppose in the middle of the month you need the billing statements for just a few select customers. There is no easy way of doing this. You have to run the complete batch process in the middle of the month and then separate out the statements you need. File-oriented systems are inadequate to face the challenges of increasing demand for information. Especially when companies care for information as a key asset, the earlier file-oriented data systems possess severe limitations. Let us discuss the important limitations so that we can appreciate how database systems overcome these shortcomings. Uncontrolled Data Redundancy In file-oriented systems, each application has its own set of files. Each application creates and stores data just for the use of that application. For example, in a bank, there could be three separate applications— one for checking accounts, one for savings accounts, and another one for loan WHY DATABASE SYSTEMS? 13 CUSTOMER MASTER FILE CustNo CustName Address Country 1000 Allbooks Book Store 5757 Westheimer, Houston, TX 77057 U.S.A. 1010 Akito Books Chiyoda-ku, Tokyo 100 Japan 1040 Robert Smith Ltd. 10 Bonds St., London W1A 2AA U.K. 2050 Sally Orobetz 8 Hazelton Ave., Toronto, Ontario M5R 2E1 Canada BOOK MASTER FILE ISBN Title Author PubId DB Design Carey DW Fundamentals McMillan Art Appreciation Stewart 2093356790 2101155897 1558712215 3456765432 Existentialism Ernst 100 200 300 400 SALESPERSON FILE SalRepId SalRepName Office Comm% Williams Chicago Harreld London Swamy Toronto 10 20 30 40 Katzman Munich 13 12 9 10 SALE TRANSACTION FILE SalDate CustNo SalRepId ISBN Qty Amount 6-Apr 799.50 10-Apr 699.50 19-Apr 1,000.50 24-Apr 1000 1010 1040 2050 10 20 30 40 2093356790 2101155897 1558712215 3456765432 10 10 20 10 750.00 PUBLISHER FILE PubId PublisherName Country Ron Fairchild USA Crosley U.K. Summer Hill Canada 100 200 300 400 Ully Wille Germany PAYMENT TRANSACTION FILE PymtDte CustNo PayMethod Amount 13-Apr Amex 600.00 22-Apr Visa 500.00 24-Apr Check 800.00 30-Apr 1000 1010 1040 2050 Visa 650.00 Figure 1-4 Progressive Book Distributors: files.
- 41. accounts. If a bank customer has a checking account, a savings account, and a loan account, data about that customer such as name and address are kept separately in each of these applications. There is unnecessary and uncontrolled duplication of the same data in the bank’s computer files. Similarly, the possibility of data duplication exists in the inpatient and outpatient accounts of a medical center. In an auction business, data duplication is possible in sellers’ and buyers’ accounts. Obviously, data duplication results in wasted storage space. In the bank example, it is very likely that many customers have both checking and savings accounts. In auction businesses, dealers of art and other such items are customers recorded in both sellers’ and buyers’ account applications. In these cases, the wastage of storage space can be enormous. Multiple input of same data item also requires extra time and resources that could be applied for other, useful purposes. Inconsistent Data Data redundancy or duplication of data in your computer files can cause serious inconsistency in the data. Suppose a bank customer has both checking and savings accounts. If that person’s name, address, or both are different in the two accounts, then the data about that customer are inconsistent in the bank’s files. Which set of data is correct? It is possible that the name of that customer in one system is correct and the address as recorded in the other application is correct. Inconsistency of data is a direct result of data duplication. Field sizes and formats of the same data item might be different in the various applications. In the checking and savings accounts, there could be just one long field for the address to be recorded in textual format. The loan account, being a later application, could have separate fields for street address, city, state, and zip code. 14 THE DATABASE APPROACH SORT PAYMENTS APPLY PAYMENTS SORT SALES APPLY SALES/PRINT STMNTS Payment Trans. File Sorted Payments Sale Trans. File Sorted Sales Customer Master File Updated Customer File Book Master File Updated Customer File Billing Statements Figure 1-5 Flowchart for billing application.
- 42. Such variations are likely causes for data integrity problems. Variations in names and addresses may cause erroneous printing of names and addresses on documents mailed to customers. Inflexibility When an application cannot adapt to changing requirements, we say that the application is inflexible. By the very nature of sequential files, a file- oriented system can process transactions only in batch mode. That is, transactions are accumulated and processed as batches. You cannot print an invoice for a single customer for a single sale. Sequential files allow retrieval of data records, one at a time, in sequence. Such files do not possess the flexibility to meet new and chang- ing information requirements. Suppose you are interested in finding and listing all the purchases made by cus- tomers in Japan for the past three months. Or you want a list of all customers in a certain zip code range. It is very difficult to satisfy such ad hoc queries in a file- oriented system without reprogramming. Limited Data Sharing Consider two typical applications, namely, order process- ing and inventory control. Each of these applications needs data on products. But data on products are repeated in each of these two applications when the business depends on file-oriented data systems. There is no sharing of data on products between the two applications. If product descriptions of certain products are changed, these changes must be made in both applications. Difficult Data Integration Let us get back to the bank example with separate cus- tomer files in the checking, savings, and loan applications. If you wanted to combine data from these applications and send consolidated statements to customers showing the transactions in all three accounts, it would be nearly impossible with file-oriented data systems. You would have to run special programs to extract banking transactions from each application. Then you would have to come up with methods for matching customer accounts from each application and consolidate the transactions in a single statement, which is not an easy task. The proliferation of files and duplication of data continue as each new application is implemented with its own set of files. Poor Enforcement of Standards and Controls Standards relate to data names, formats, value restrictions, and access controls. When duplicated data are spread across many applications, it is extremely difficult to enforce standards. For example, if the standard in your company is for the customer name field to be 35 bytes, then you will have to impose this standard, not in one place, but in many applica- tions that store customer names. Suppose you have to include a business rule that the employee daily wage rate must be between 0 and 100; you may have to stipu- late this rule in at least two different applications, namely, payroll and human resources. Problems with the resolution of homonyms and synonyms deserve special atten- tion. File-oriented data systems are likely to have problems with these. Homonyms. If a single field name represents two or more objects in different appli- cations, it is called a homonym. For example, the field name balance may represent WHY DATABASE SYSTEMS? 15
- 43. the checking balance in the checking accounts application. The same field name balance may also represent the savings balance in the savings accounts application. In this case, the term balance is a homonym. In file-oriented data systems, it is hard to control homonyms. Synonyms. If different field names in different applications represent the same object, these names are known as synonyms. As an example, consider how a student may be referred to in a college data system. In the student registration system, the student may be referred to by the field name student-number. On the other hand, in the majors and graduation system, the student may be referred to by the field name candidate-number. The terms student-number and candidate-number are synonyms. In file-oriented data systems, controlling synonyms is difficult. Excessive Program Maintenance How is program maintenance a problem in file-oriented systems? Consider the coding of computer programs in file-oriented applications. These programs are usually written in third-generation languages like COBOL. A program in languages like COBOL contains two distinct sections. One section of the program, namely, FD or file definition section, has the structures of the files used in the program embedded within the program itself. The other section has the processing logic. Data structures and processing logic are interconnected and combined together in the program. This means that reference to data is not independent of the processing logic. There is no data independence. What is the effect of the lack of data independence in file-oriented systems? Con- sider all the computer programs that use the customer file for processing. In each of these programs,the structure of the customer file is embedded within the program itself. What happens when a new field such as cellular phone number is added to the customer record? Every one of the programs using the customer file need to be changed and recompiled, irrespective of whether the program uses the cellular phone number field or not. Lack of data independence results in excessive program maintenance. Productivity Losses Two main factors cause reduction in productivity while using file-oriented systems: • The same data need to be maintained in multiple places. • Because of lack of data independence, multiple programs need to be changed frequently. Database Systems Meet the Challenges As the demand for information escalated, it became urgent to overcome the limi- tations of file-oriented data systems. With these limitations, companies could not meet the requirements of increased demand for information. They needed a dif- ferent approach to storing, retrieving, and managing data. They could not afford the productivity losses. They could not waste space because of data duplication in file-oriented systems. Specialists at Rockwell and General Electric began to work on better methods for managing data. These methods attempted to overcome the limitations of 16 THE DATABASE APPROACH
- 44. file-oriented systems. Data and processing logic had to be separated so as to improve programmer productivity. The new approach of using databases instead of conventional flat files addressed the challenges for meeting the increased demand for information. The database approach overcame the limitations of the earlier data systems and produced enormous benefits. Let us review the specific benefits and understand in what way the database approach is superior to the earlier data systems. Minimal Data Redundancy Unlike file-oriented data systems where data are duplicated among various applications, database systems integrate all the data into one logical structure. Duplication of data is minimized. Wastage of storage space is eliminated. Going back to the bank example, with a database, customer data is not duplicated in the checking account, savings account, and loan account applications. Customer data is entered and maintained in only one place in the database. Sometimes, in a database, a few data elements may have to be duplicated. Let us say that product data consist of product number, description, price, and the corre- sponding product line number. All the fields relating to product line data are kept separately. Whenever the details of products and product lines are needed in appli- cations, both data structures are retrieved from the database. Suppose a heavily used product forecast application needs all the details of the product from product data and just the product line description from the product line data. In that case, it will be efficient for the product data to duplicate the product line description from the product line data. Thus, in some instances, data duplication is permitted in a data- base for the purpose of access efficiency and performance improvement. However, such data duplications are kept to a minimum. Data Integrity Data integrity in a database means reduction of data inconsistency. Because of the elimination or control of data redundancy, a database is less prone to errors creeping in through data duplication. Field sizes and field formats are the same for all applications. Each application uses the same data from one place in the database. In a bank, names and addresses will be the same for checking account, savings account, and loan applications. Data Integration In a database, data objects are organized into single logical data structures. For example, in file-oriented data systems, data about employees are scat- tered among the various applications. The payroll application contains employee name and address, social security number, salary rate, deductions, and so on. The pension plan application contains pension data about each employee, whereas the human resources application contains employee qualifications, skills, training, and education. However, all data about each employee are integrated and stored together in a database. So, in a database, data about each business object are integrated and stored sep- arately as customer, order, product, invoice, manufacturer, sale, and so on. Data inte- gration enables users to understand the data and the relationships among data structures easily. Programmers needing data about a business object can go to one place to get the details. For example, data about orders are consolidated in one place as order data. WHY DATABASE SYSTEMS? 17
- 45. Data Sharing This benefit of database systems follows from data integration. The various departments in any enterprise need to share the company’s data for proper functioning. The sales department needs to share the data generated by the account- ing department through the billing application. Consider the customer service department. It needs to share the data generated by several applications. The cus- tomer service application needs information about customers, their orders, billings, payments, and credit ratings. With data integration in a database, the application can get data from distinct and consolidated data structures relating to customer, orders, invoices, payments, and credit status. Data sharing is a major benefit of database systems. Each department shares the data in the database that are most pertinent to it. Departments may be interested in data structures as follows: Sales department—Customer/Order Accounting department—Customer/Order/Invoice/Payment Order processing department—Customer/Product/Order Inventory control department—Product/Order/Stock Quantity/Back Order Quantity Database technology lets each application use the portion of the database that is needed for that application. User views of the database are defined and con- trolled. We will have more to say about user views in later chapters. Uniform Standards We have seen that, because of the spread of duplicate data across applications in file-oriented data systems, standards cannot be enforced easily and completely. Database systems remove this difficulty. As data duplication is con- trolled in database systems and as data is consolidated and integrated, standards can be implemented more easily. Restrictions and business rules for a single data element need to be applied in only one place. In database systems, it is possible to eliminate problems from homonyms and synonyms. Security Controls Information is a corporate asset and, therefore, must be pro- tected through proper security controls. In file-oriented systems, security controls cannot be established easily. Imagine the data administrator wanting to restrict and control the use of data relating to employees. In file-oriented systems, control has to be exercised in all applications having separate employee files. However, in a database system, all data about employees are consolidated, integrated, and kept in one place. Security controls on employee data need to be applied in only one place in the database. Database systems make centralized security controls possible. It is also easy to apply data access authorizations at various levels of data. Data Independence Remember the lack of data independence in file-oriented systems where computer programs have data structure definitions embedded within the programs themselves. In database systems, file or data definitions are separated out of the programs and kept within the database itself. Program logic and data structure definitions are not intricately bound together. In a client/server environ- ment, data and descriptions of data structures reside on the database server, whereas 18 THE DATABASE APPROACH
- 46. the code for application logic executes on the client machine or on a separate appli- cation server. Reduced Program Maintenance This benefit of database systems results pri- marily from data independence in applications. If the customer data structure changes by the addition of a field for cellular phone numbers, then this change is made in only one place within the database itself. Only those programs that need the new field need to be modified and recompiled to make use of the added piece of data. Within limits, you can change programs or data independently. Simpler Backup and Recovery In a database system, generally all data are in one place. Therefore, it becomes easy to establish procedures to back up data. All the relationships among the data structures are also in one place. The arrangement of data in database systems makes it easier not only for backing up the data but also for initiating procedures for recovery of data lost because of malfunctions. THE DATABASE APPROACH What are the implications when an organization makes the transition from file- oriented systems to database systems? When an organization changes its approach to management of data and adopts database technology, what are the significant effects in the way business is conducted? What happens when an organization embraces the database approach? Let us find answers to such questions. We will discuss the way applications are designed and implemented with database systems. We will explore the basic con- cepts of the database approach. We will also review some of the types of databases and how these are used. We have reviewed the benefits of database systems and established how they are superior to the earlier file-oriented data systems. We caught a glimpse of the fea- tures of database systems that produce several benefits. Database systems reduce data redundancy, integrate corporate data, and enable information sharing among the various groups in the organization. Now you are ready for an initial, formal def- inition of a database. Database: A Formal Definition Let us examine the following definition: A database is an ordered collection of related data elements intended to meet the infor- mation needs of an organization and designed to be shared by multiple users. Note the key terms in the definition: Ordered collection. A database is a collection of data elements. Not just a random assembly of data structures, but a collection of data elements put together deliber- ately with proper order. The various data elements are linked together in the most logical manner. THE DATABASE APPROACH 19
- 47. Related data elements. The data elements in a database are not disjointed struc- tures without any relationships among them. These are related among themselves and also pertinent to the particular organization. Information needs. The collection of data elements in a database is there for a specific purpose. That purpose is to satisfy and meet the information needs of the organization. In a database for a bank, you will find data elements that are pertinent to the bank’s business. You will find customer’s bank balances and ATM transactions. You will not find data elements relating to a student’s major and examination grades that belong in a database for a university. You will not find a patient’s medical history that really belongs in a database for a medical center. Shared. All authorized users in an organization can share the information stored in its database. Integrated information is kept in the database for the purpose of sharing so that all user groups may collaborate and accomplish the organization’s objectives. Data-Driven, Not Process-Driven When an organization adopts a database approach to managing corporate data, the very method of designing and implementing applications changes. Traditionally, when you design and implement an application with file-oriented data systems, you use a process-driven approach. That method changes with database systems. You shift your design and implementation method to a data-driven approach. Figure 1-6 shows the difference between the two methods. In both methods, you begin with the definition of requirements. However, there is an essential difference between the two methods. In the process-driven method, 20 THE DATABASE APPROACH Requirements definition Requirements definition Data Design Data Design Process Design Process Design Imple- mentation Imple- mentation Data-driven approach Process-driven approach versus Figure 1-6 Data-driven, not process-driven.
- 48. you collect requirements for the outputs and the processes and then determine the inputs. Determination of the inputs leads to the design of the data files. In the data-driven method, you gather requirements about the business objects that are pertinent to the business. You collect the data required to be included about these objects. Then you design the database to support the business. After this, the design of the initial processes follows. Right away, you can see the advantage of the data-driven approach. Although you are interested in supporting the initial processes, because you have designed the database to contain all data relevant to the business, you will find it easy to add further processes later on. Data-driven approach provides enormous flexibility to provide for new and additional processing requirements at a later time. In practice, companies adopting the database approach use a combination of both methods, although the data-driven method dominates the application development phases. Basic Concepts You are now beginning to appreciate the significance of the database approach. You are discerning the major benefits of developing and using applications in a database environment. Before proceeding further, let us review a few fundamental concepts and become familiar with some key terminology. Data Repository All data in the database reside in a data repository. This is the data storage unit where physical data files are kept. The data repository contains the physical data. Mostly, it is a central place of storage for the data content. Data Dictionary The data repository contains the actual data. Let us say that you want to keep data about the customers of your company in your database. The struc- ture of a customer’s data could include fields such as customer name, customer address, city, state, zip code, phone number, and so on. Data about a particular customer could be as follows in the respective fields: Jane Smith/1234 Main Street/Piscataway/NJ/08820.There are two aspects of the data about customers. One aspect is the structure of the data consisting of the field names, field sizes, data types, and so on. This part is the structure of the data for customers. The other part is the actual data for each customer consisting of the actual data values in the various fields. The first part relating to the structure resides separately in storage, and this is called the data dictionary or data catalog. A data dictionary contains the structures of the various data elements in the database. It also contains the relationships among data elements. The other part relating to the actual data about individual customers resides in the data repository. The data dictionary and the data reposi- tory work together to provide information to users. Database Software Are Oracle and Informix databases? Oracle and Informix are really the software that manages data. These are database software or database management systems. Database software supports the storing, retrieving, and updat- ing of data in a database. Database software is not the database itself. The software helps you store, manage, and protect the data in a database. THE DATABASE APPROACH 21
- 49. Data Abstraction Consider the example of customer data again. Data about each customer consist of several fields such as customer name, street address, city, state, zip code, credit status, and so on. We can look at customer data at three levels. The customer service representative can look at the customer from his or her point of view as consisting of only the fields that are of interest to the representative. This may be just customer name, phone number, and credit status. This is one level. The next level is the structure of the complete set of fields in customer data. This level is of interest to the database designer and application programmer. Another level is of interest to the database administrator, who is responsible for designing the physical layout for storing the data in files on disk storage. Now go through the three levels. The customer service representative is just inter- ested in what he or she needs from customer data, not the entire set of fields or how the data is physically stored on disk storage. The complexities of the other two levels may be hidden from the customer service representative. Similarly,the physical level of how the data is stored on disk storage may be hidden from the application pro- grammer. Only the database administrator is interested in all three levels. This concept is the abstraction of data—the ability to hide the complexities of data design at the levels where they are not required. The database approach provides for data abstraction. Data Access The database approach includes the fundamental operations that can be applied to data. Every database management system provides for the fol- lowing basic operations: • READ data contained in the database • ADD data to the database • UPDATE individual parts of the data in the database • DELETE portions of the data in the database Database practitioners refer to these operations by the acronym CRUD: • C—Create or add data • R—Read data • U—Update data • D—Delete data Transaction Support Imagine the business function of entering an order from a customer into the computer system. The order entry clerk types in the customer number, the product code, and the quantity ordered. The order entry program reads the customer data and allows the clerk to sight verify the customer data, reads product data and displays the product description, reads inventory data, and finally updates inventory or creates a back order if inventory is insufficient. All these tasks performed by the order entry program to enter a single order comprise a single order entry transaction. When a transaction is initiated it should complete all the tasks and leave the data in the database in a consistent state. That is, if the initial stock is 1000 units and the order is for 25 units, the stock value stored in the database after the transaction is 22 THE DATABASE APPROACH
- 50. completed must be 975 units. How can this be a problem? See what can happen in the execution of the transaction. First, the transaction may not be able to perform all its tasks because of some malfunction preventing its completion. Second, numer- ous transactions from different order entry clerks may be simultaneously looking for inventory of the same product. Database technology enables a transaction to complete a task in its entirety or back out intermediary data updates in case of mal- functions preventing completion. How Databases Are Used You now realize the use of databases for supporting the core business of an orga- nization and enabling day-to-day operations. These are production databases that support the operational systems of an enterprise. More recently, with increasing demand for information, databases fulfill another important function. Databases provide support for strategic decision making in an organization. Such decision- support databases are designed and implemented separately and differently. Pro- duction databases and decision-support databases are large-scale databases for the several users within organizations. Individuals and single departments may also use private databases. For example, a specialty department may want to send targeted mailings to specific customers and to keep these customers in a separate database. Individual business analysts may keep data and research results in a separate database just for their use. These are mass deployment individual databases. Figure 1-7 shows the separation of databases by their uses and describes some of the features. OVERVIEW OF DATA MODELS A data model represents the data requirements of an organization. You can diagrammatically show a data model with symbols and figures. Data for an OVERVIEW OF DATA MODELS 23 Production Databases Decision- Support Databases Mass Deployment Databases •Support business functions •Online transaction processing •Usage includes CRUD activities •Features include concurrency, security, transaction processing, security •Used for analysis, querying, and reporting •Generally read-only •Features include query tools and custom applications •Data warehouse and OLAP systems •Intended for single user environments •Workstation versions of database products •Ease of use important •Features include report and application generation capabilities Figure 1-7 How databases are used.
- 51. organization reside in a database. Therefore, when designing a database, you first create a data model. The model would represent the real-world data requirements. It would show the arrangement of the data structures. Database software has evolved to support different types of data models. As we try to represent real-world data requirements as close as possible in a data model, we come up with a replica of the real-world information requirements. It turns out that we can look at data requirements and create data models in a few different ways. At this stage, let us survey a few leading data models. Over time, different vendors have developed commercial database management systems to support each of these common data models. Hierarchical Let us examine the data requirements for a typical manufacturing company. Typically in manufacturing, you have major assemblies, with each major assembly consisting of subassemblies, each subassembly consisting of parts, each part consisting of subparts, and so on. In your database for the manufacturing company, you need to keep data for the assemblies, subassemblies, parts, and subparts. And the data model for manufacturing operations must represent these data requirements. Think about this data model. This model should show that an assembly contains subassemblies, a subassembly contains parts, and a part contains subparts. Immedi- ately you can observe that this data model must be hierarchical in nature, dia- gramming the assembly at the top with subassembly, part, and subpart at successive lower levels. In the business world, many data structures are hierarchical in nature. You can notice a hierarchy in department, product category, product subcategory, product line, and product. You can trace a hierarchy in division, subdivision, department, and employee. Figure 1-8 illustrates one such model showing the hierarchy of cus- tomer, order, and order line item. A customer may have one or more orders, and an order may have one or more line items, perhaps one line item for each product ordered. Let us review the key features of the hierarchical model by referring to Figure 1-8. Levels. Each data structure representing a business object is at one of the hierar- chical levels. Parent-Child Relationships. The relationship between each pair of data structures at levels next to each other is a parent-child relationship. CUSTOMER is a parent data segment whose child is the ORDER data segment. In this arrangement, a child segment can have only one parent segment but one parent segment may have mul- tiple child segments. You may want to separate orders into phone orders and mail orders. In that case, CUSTOMER may have PHONE ORDER and MAIL ORDER as two child segments. Root Segment. The data segment at the top level of the hierarchy is known as the root data segment (as in an inverted tree). 24 THE DATABASE APPROACH
- 52. Physical Pointers. How are the orders of a particular customer linked in the implementation of the hierarchical data model? These linkages are by means of physical pointers or physical storage addresses embedded within physical records in the database. Physical pointers link records of the parent segments to those of the child segments by means of parent-child forward or backward pointers. Simi- larly, forward and backward physical pointers link records of the same segment type. Network The hierarchical data model represents well any business data that inherently con- tains levels one below the other. We have just discussed how the manufacturing application deals with hierarchical levels of plant inventory with assemblies broken down into lower-level components. The hierarchical data model suits this applica- tion well. However, in the real world, most data structures do not conform to a hierarchical arrangement. The levels of data structures do not fall into nice depen- dencies one below another as in a hierarchy. In the hierarchical data model, you have noticed that each data segment at any level can have only one parent at the next higher level. In practice, many sets of related elements may not be sub- jected to such restrictions. Let us consider a common set of related data elements in a typical business. The data elements pertain to customers placing orders and making payments, salesper- sons being assigned, and salespersons being part of sales territories. All of these data elements cannot be arranged in a hierarchy. The relationships cross over among the data elements as though they form a network. Refer to Figure 1-9 and note how it represents a network arrangement and not a hierarchical arrangement. Observe the six data elements of sales territory, salesperson, customer, order, order line item, and payment as nodes in a network arrangement. OVERVIEW OF DATA MODELS 25 CUSTOMER ORDER ORDER LINE ITEM Root Segment Parent Segment Child Segment Parent Segment Child Segment Relationship links through physical pointers Figure 1-8 Hierarchical data model.
- 53. The network data model overcomes some of the limitations of the hierarchical data model. The network data model is more representative of real-world infor- mation requirements than the hierarchical model. The network data model can represent most business information. Let us go over the key features of the network model by referring to Figure 1-9. Levels. As in most real-world situations, no hierarchical levels exist in the network model. The lines in a network data model simply connect the appropriate data struc- tures wherever necessary without the restriction of connecting only successive levels as in the hierarchical model. Note the lines connecting the various data structures with no restrictions. Record Types. In the network data model, each data structure is known as a record type. For example, the CUSTOMER record type represents the data content of all customers. The ORDER record type represents the data content of all orders. Relationships. The network data model expresses relationships between two record types by designating one as the owner record type and the other as the member record type. For each occurrence of an owner record type, there are one or more occurrences of the member record type. The owner record type may be reckoned as the parent and the member record type as the child. In a sense, the owner record type “owns” the corresponding member record type. Each member type with its corresponding owner record type is known as a set. A set represents the relationship between an owner and a member record type. Multiple Parents. Look at the ORDER member record type. For ORDER there are two parents or owner records, namely, CUSTOMER and PAYMENT. In other 26 THE DATABASE APPROACH CUSTOMER ORDER ORDER LINE ITEM Relationship links through physical pointers SALES TERRITORY SALES PERSON PAYMENT Owner record type Owner record type Member record type Member record type Member record type Owner record type Owner record type Member record type Member record type Owner record type Figure 1-9 Network data model.
- 54. words, for one occurrence of CUSTOMER, one or more occurrences of ORDER exist. Similarly,for one occurrence of PAYMENT there are one or more occurrences of ORDER. By definition, a hierarchical data model cannot represent this kind of data arrangement with two parents for one child data structure. Physical Pointers. Just as in the case of the hierarchical data model, related occurrences of two different record types in a network model are connected by physical pointers or physical storage addresses embedded within physical records in the database. Physical pointers link occurrences of an owner record type with the corresponding occurrences of the member record type. Within each record type itself the individual occurrences may be linked to one another by means of forward and backward pointers. Relational This book will provide you with in-depth discussions about the relational model. This data model is superior to the earlier models. Dr. E. F. Codd, the celebrated father of the relational model, stipulated the rules and put this model on a solid mathematical foundation. At this stage, however, we want to introduce the rela- tional model as a superior data model that addresses the limitations of the earlier data models. The earlier hierarchical data model is suitable for data structures that are natu- rally hierarchical, with each data structure placed at a certain level in the hierarchy. However, in the business arena, many of the data structures and their relationships cannot be readily placed in a hierarchical arrangement. The network data model evolved to dispense with the arbitrary restriction of the hierarchical model. Never- theless, in both of these models, you need physical pointers to connect related data occurrences. This is a serious drawback because you have rewrite the physical addresses in the data records every time you reorganize the data, move the data to a different storage area, or change over to another storage medium. The relational model establishes the connections between related data occurrences by means of logical links implemented through foreign keys. Figure 1-10 illustrates the relational data model. Let us note the key features of the relational data model by referring to Figure 1-10. Levels. Just like the network data model, no hierarchical levels are present in the relational model. The lines in a relational data model simply indicate the relation- ships between the appropriate data structures wherever necessary without the restriction of connecting only successive levels as in the hierarchical model. As in the network model, note the lines connecting the various data structures with no restrictions. Relations or Tables. The relational model consists of relations. A relation is a two-dimensional table of data observing relational rules. For example, the CUS- TOMER relation represents the data content of all customers. The ORDER rela- tion represents the data content of all orders. OVERVIEW OF DATA MODELS 27
- 55. Another Random Document on Scribd Without Any Related Topics
- 56. down, with his musket on his shoulder, not far off. No wonder that he shuddered to his inmost marrow, and buried his face in his mantle, as he moved slowly up and down. Maria had wrapped herself in the black faldetta, that her form might be the less distinct in the darkness of the night. She breathed a prayer to the Holy Virgin, the Mother of Sorrows, that she would help her, and then she walked swiftly to the scaffold. It was the seventh body—she loosed Bernardo; her heart, and a faint gleam from his dead face, told her that it was he, even in the dark night. Maria took the dead man in her arms, upon her shoulder. She had become strong, as if with the strength of a man. She bore the corpse into the Church of St. Francis. There she sat down exhausted, on the steps of an altar, over which the lamp of the Mother of God was burning. The dead Bernardo lay upon her knees, as the dead Christ once lay upon the knees of Mary. In the south they call this group Pietà. Not a sound in the church. The lamp glimmers above the altar. Outside, a gust of wind that whistles by. Maria rose. She let the dead Bernardo gently down upon the steps of the altar. She went to the spot where the grave of Bernardo's parents lay. She opened the grave. Then she took up the dead body. She kissed him, and lowered him into the grave, and again shut it. Maria knelt long before the Mother of God, and prayed that Bernardo's soul might have peace in heaven; and then she went silently away to her house, and to her chamber. When morning broke, Bernardo's corpse was missing from among the dead bodies before the convent. The news flew through the village, and the soldiers drummed alarm. It was not doubted that the Leccia family had removed their kinsman during the night from the scaffold; and instantly their house was forced, its inmates taken prisoners, and thrown chained into a jail. Guilty of capital crime,
- 57. according to the law that had been proclaimed, they were to suffer the penalty, although they denied the deed. Maria Gentili heard in her chamber what had happened. Without saying a word, she hastened to the house of the Count de Vaux, who had come to Oletta. She threw herself at his feet, and begged the liberation of the prisoners. She confessed that it was she who had done that of which they were supposed to be guilty. "I have buried my betrothed," said she; "death is my due, here is my head; but restore their freedom to those that suffer innocently." The Count at first refused to believe what he heard; for he held it impossible both that a weak girl should be capable of such heroism, and that she should have sufficient strength to accomplish what Maria had accomplished. When he had convinced himself of the truth of her assertions, a thrill of astonishment passed through him, and he was moved to tears. "Go," said he, "generous-hearted girl, yourself release the relations of your lover; and may God reward your heroism!" On the same day the other six corpses were taken from the scaffold, and received a Christian burial. CHAPTER VII. A RIDE THROUGH THE DISTRICT OF OREZZA TO MOROSAGLIA. I wished to go from Oreto to Morosaglia, Paoli's native place, through Orezza. Marcantonio had promised to accompany me, and to provide good horses. He accordingly awoke me early in the morning, and made ready to go. He had put on his best clothes, wore a velvet jacket, and had shaved himself very smoothly. The
- 58. women fortified us for the journey with a good breakfast, and we mounted our little Corsican horses, and rode proudly forth. It makes my heart glad yet to think of that Sunday morning, and the ride through this romantic and beautiful land of Orezza—over the green hills, through cool dells, over gushing brooks, through the green oak-woods. Far as the eye can reach on every side, those shady, fragrant chestnut-groves; those giants of trees, in size such as I had never seen before. Nature has here done everything, man so little. His chestnuts are often a Corsican's entire estate; and in many instances he has only six goats and six chestnut-trees, which yield him his polleta. Government has already entertained the idea of cutting down the forests of chestnuts, in order to compel the Corsican to till the ground; but this would amount to starving him. Many of these trees have trunks twelve feet in thickness. With their full, fragrant foliage, long, broad, dark leaves, and fibred, light-green fruit-husks, they are a sight most grateful to the eye. Beyond the paese of Casalta, we entered a singularly romantic dell, through which the Fiumalto rushes. You find everywhere here serpentine, and the exquisite marble called Verde Antico. The engineers called the little district of Orezza the elysium of geology; the waters of the stream roll the beautiful stones along with them. Through endless balsamic groves, up hill and down hill, we rode onwards to Piedicroce, the principal town of Orezza, celebrated for its medicinal springs; for Orezza, rich in minerals, is also rich in mineral waters. Francesco Marmocchi says, in his geography of the island: "Mineral springs are the invariable characteristic of countries which have been upheaved by the interior forces. Corsica, which within a limited space presents the astonishing and varied spectacle of the thousandfold workings of this ancient struggle between the heated interior of the earth and its cooled crust, was not likely to form an exception to this general rule."
- 59. Corsica has, accordingly, its cold and its warm mineral springs; and although these, so far as they have been counted, are numerous, there can be no doubt that others still remain undiscovered. The natural phenomena of this beautiful island, and particularly its mineralogy, have by no means as yet had sufficient attention directed to them. Up to the present time, fourteen mineral springs, warm and cold, are accurately and fully known. The distribution of these salubrious waters over the surface of the island, more especially in respect to their temperature, is extremely unequal. The region of the primary granite possesses eight, all warm, and containing more or less sulphur, except one; while the primary ophiolitic and calcareous regions possess only six, one alone of which is warm. The springs of Orezza, bursting forth at many spots, lie on the right bank of the Fiumalto. The main spring is the only one that is used; it is cold, acid, and contains iron. It gushes out of a hill below Piedicroce in great abundance, from a stone basin. No measures have been taken for the convenience of strangers visiting the wells; these walk or ride under their broad parasols down the hills into the green forest, where they have planted their tents. After a ride of several hours under the burning sun, and not under a parasol, I found this vehemently effervescing water most delicious. Piedicroce lies high. Its slender church-tower looks airily down from the green hill. The Corsican churches among the mountains frequently occupy enchantingly beautiful and bold sites. Properly speaking, they stand already in the heavens; and when the door opens, the clouds and the angels might walk in along with the congregation. A majestic thunderstorm was flaming round Piedicroce, and echoed powerfully from hill to hill. We rode into the paese to escape the torrents of rain. A young man, fashionably dressed, sprang out of a house, and invited us to enter his locanda. I found other two
- 60. gentlemen within, with daintily-trimmed beard and moustache, and of very active but polished manners. They immediately wished to know my commands; and nimble they were in executing them—one whipped eggs, another brought wood and fire, the third minced meat. The eldest of them had a nobly chiselled but excessively pale face, with a long Slavonic moustache. So many cooks to a simple meal, and such extremely genteel ones, I was now for the first time honoured with. I was utterly amazed till they told me who they were. They were two fugitive Modenese, and a Hungarian. The Magyar told me, as he stewed the meat, that he had been seven years lieutenant-general. "Now I stand here and cook," he added; "but such is the way of the world, when one has come to be a poor devil in a foreign country, he must not stand on ceremony. We have set up a locanda here for the season at the wells, and have made very little by it." As I looked at his pale face—he had caught fever at Aleria—I felt touched. We sat down together, Magyar, Lombard, Corsican, and German, and talked of old times, and named many names of modern celebrity or notoriety. How silent many of these become before the one great name, Paoli! I dare not mention them beside him; the noble citizen, the man of intellect and action, will not endure their company. The storm was nearly over, but the mountains still stood plunged in mist. We mounted our horses in order to cross the hills of San Pietro and reach Ampugnani. Thunder growled and rolled among the misty summits, and clouds hung on every side. A wild and dreary sadness lay heavily on the hills; now and then still a flash of lightning; mountains as if sunk in a sea of cloud, others stretching themselves upwards like giants; wherever the veil rends, a rich landscape, green groves, black villages—all this, as it seemed, flying past the rider; valley and summit, cloister and tower, hill after hill, like dream- pictures hanging among clouds. The wild elemental powers, that sleep fettered in the soul of man, are ready at such moments to burst their bonds, and rush madly forth. Who has not experienced
- 61. this mood on a wild sea, or when wandering through the storm? and what we are then conscious of is the same elemental power of nature that men call passion, when it takes a determinate form. Forward, Antonio! Gallop the little red horses along this misty hill, fast! faster! till clouds, hills, cloisters, towers, fly with horse and rider. Hark! yonder hangs a black church-tower, high up among the mists, and the bells peal and peal Ave Maria—signal for the soul to calm itself. The villages are here small, picturesquely scattered everywhere among the hills, lying high or in beautiful green valleys. I counted from one point so many as seventeen, with as many slender black church-towers. We passed numbers of people on the road; men of the old historic land of Orezza and Rostino, noble and powerful forms; their fathers once formed the guard of Paoli. At Polveroso, we had a magnificent glimpse of a deep valley, in the middle of which lies Porta, the principal town of the little district of Ampugnani, embosomed in chestnuts, now dripping with the thunder-shower. Here stood formerly the ancient Accia, a bishopric, not a trace of which remains. Porta is an unusually handsome place, and many of its little houses resemble elegant villas. The small yellow church has a pretty façade, and a surprisingly graceful tower stands, in Tuscan fashion, as isolated campanile or belfry by its side. From the hill of San Pietro, you look down into the rows of houses, and the narrow streets that group themselves about the church, as into a trim little theatre. Porta is the birthplace of Sebastiani. The mountains now become balder, and more severe in form, losing the chestnuts that previously adorned them. I found huge thistles growing by the roadside, large almost as trees, with magnificent, broad, finely-cut leaves, and hard woody stem. Marcantonio had sunk into complete silence. The Corsicans speak little, like the Spartans; my host of Oreto was dumb as Harpocrates. I had ridden with him a whole day through the mountains, and, from morning till evening had never been able to draw him into conversation. Only now and then he threw out some naïve question: "Have you
- 62. cannons? Have you hells in your country? Do fruits grow with you? Are you wealthy?" After Ave Maria, we at length reached the canton of Rostino or Morosaglia, the country of Paoli, the most illustrious of all the localities celebrated in Corsican history, and the central point of the old democratic Terra del Commune. We were still upon the Campagna, when Marcantonio took leave of me; he was going to pass the night in a house at some distance, and return home with the horses on the morrow. He gave me a brotherly kiss, and turned away grave and silent; and I, happy to find myself in this land of heroes and free men, wandered on alone towards the convent of Morosaglia. I have still an hour on the solitary plain, and, before entering Paoli's house, I shall continue the history of his people and himself at the point where I left off. CHAPTER VIII. PASQUALE PAOLI. "Il cittadin non la città son io."—Alfieri's Timoleon. After Pasquale Paoli and his brother Clemens, with their companions, had left Corsica, the French easily made themselves masters of the whole island. Only a few straggling guerilla bands protracted the struggle a while longer among the mountains. Among these, one noble patriot especially deserves the love and admiration of future times—the poor parish priest of Guagno—Domenico Leca, of the old family of Giampolo. He had sworn upon the Gospels to abide true to freedom, and to die sooner than give up the struggle. When the whole country had submitted, and the enemy summoned him to lay
- 63. down his arms, he declared that he could not violate his oath. He dismissed those of his people that did not wish any longer to follow him, and threw himself, with a faithful few, into the hills. For months he continued the struggle, fighting, however, only when he was attacked, and tending wounded foes with Christian compassion when they fell into his hands. He inflicted injury on none except in honourable conflict. In vain the French called on him to come down, and live unmolested in his village. The priest of Guagno wandered among the mountains, for he was resolved to be free; and when all had forsaken him, the goat-herds gave him shelter and sustenance. But one day he was found dead in a cave, whence he had gone home to his Master, weary and careworn, and a free man. A relative of Paoli and friend of Alfieri—Giuseppe Ottaviano Savelli—has celebrated the memory of the priest of Guagno in a Latin poem, with the title of Vir Nemoris—The Man of the Forest. Other Corsicans, too, who had gone into exile to Italy, landed here and there, and attempted, like their forefathers, Vincentello, Renuccio, Giampolo, and Sampiero, to free the island. None of these attempts met with any success. Many Corsicans were barbarously dragged off to prison—many sent to the galleys at Toulon, as if they had been helots who had revolted against their masters. Abattucci, who had been one of the last to lay down arms, falsely accused of high treason and convicted, was condemned in Bastia to branding and the galleys. When Abattucci was sitting upon the scaffold ready to endure the execution of the sentence, the executioner shrank from applying the red-hot iron. "Do your duty," cried a French judge; the man turned round to the latter, and stretched the iron towards him, as if about to brand the judge. Some time after, Abattucci was pardoned. Meanwhile, Count Marbœuf had succeeded the Count de Vaux in the command of Corsica. His government was on the whole mild and beneficial; the ancient civic regulations of the Corsicans, and their statutes, remained in force; the Council of Twelve was restored, and the administration of justice rendered more efficient. Efforts were
- 64. also made to animate agriculture, and the general industry of the now utterly impoverished country. Marbœuf died in Bastia in 1786, after governing Corsica for sixteen years. When the French Revolution broke out, that mighty movement absorbed all private interests of the Corsicans, and these ardent lovers of liberty threw themselves with enthusiasm into the current of the new time. The Corsican deputy, Saliceti, proposed that the island should be incorporated with France, in order that it might share in her constitution. This took place, in terms of a decree of the Legislative Assembly, on the 30th of November 1789, and excited universal exultation throughout Corsica. Most singular and contradictory was the turn affairs had taken. The same France, that twenty years before had sent out her armies to annihilate the liberties and the constitution of Corsica, now raised that constitution upon her throne! The Revolution recalled Paoli from his exile. He had gone first to Tuscany, and thereafter to London, where the court and ministers had given him an honourable reception. He lived very retired in London, and little was heard of his life or his employment. Paoli made no stir when he came to England; the great man who had led the van for Europe on her new career, withdrew into silence and obscurity in his little house in Oxford Street. He made no magniloquent speeches. All he could do was to act like a man, and, when that was no longer permitted him, be proudly silent. The scholar of Corte had said in his presence, in the oration from which I have quoted: "If freedom were to be gained by mere talking, then were the whole world free." Something might be learned from the wisdom of this young student. When Napoleon, like a genuine Corsican, taking refuge as a last resource in an appeal to hospitality, claimed that of England from on board the Bellerophon, he compared himself to Themistocles when in the position of a suppliant for protection. He was not entitled to compare himself with the great citizen of Greece; Pasquale Paoli alone was that exiled Themistocles!
- 65. Here are one or two letters of this period:— PAOLI TO HIS BROTHER CLEMENS, (Who had remained in Tuscany.) "London, Oct. 3, 1769.—I have received no letters from you. I fear they have been intercepted, for our enemies are very adroit at such things.... I was well received by the king and queen. The ministers have called upon me. This reception has displeased certain foreign ministers: I hear they have lodged protests. I have promised to go on Sunday into the country to visit the Duke of Gloucester, who is our warm friend. I hope to obtain something here for the support of our exiled fellow-countrymen, if Vienna does nothing. The eyes of people here are beginning to be opened; they acknowledge the importance of Corsica. The king has spoken to me very earnestly of the affair; his kindness to me personally made me feel embarrassed. My reception at court has almost drawn upon me the displeasure of the opposition; so that some of them have begun to lampoon me. Our enemies sought to encourage them, letting it be understood with a mysterious air, that I had sold our country; that I had bought an estate in Switzerland with French gold, that our property had not been touched by the French; and that they had an understanding with these ministers, as they too are sold to France. But I believe that all are now better informed; and every one approved of my resolution not to mix myself up with the designs of parties; but to further by all means that for which it is my duty to labour, and for the advancement of which all can unite, without compromising their individual relations. "Send me an accurate list of all our friends who have gone into banishment—we must not be afraid of expense; and send me news of Corsica. The letters must come under the addresses of private friends, otherwise they do not reach me. I enjoy perfect health. This climate appears to me as yet very mild. "The Campagna is always quite green. He who has not seen it can have no conception of the loveliness of spring. The soil of England is crisped like the waves of the sea when the wind moves them lightly. Men here, though excited by political faction, live, as far as regards overt acts of violence, as if they were the most intimate friends: they are benevolent, sensible, generous in all things; and they are happy under a constitution than which there can be no better. This city is a world; and it is without doubt a finer town than all the rest put together. Fleets seem to enter its river every moment; I believe that
- 66. Rome was neither greater nor richer. What we in Corsica reckon in paoli, people here reckon in guineas, that is, in louis-d'ors. I have written for a bill of exchange; I have refused to hear of contributions intended for me personally, till I know what conclusion they have come to in regard to the others; but I know that their intentions are good. In case they are obliged to temporize, finding their hands tied at present, they will be ready the first war that breaks out. I greet all; live happy, and do not think on me." CATHERINE OF RUSSIA TO PASQUALE PAOLI. "St. Petersburg, April 27, 1770. "Monsieur General de Paoli!—I have received your letter from London, of the 15th February. All that Count Alexis Orloff has let you know of my good intentions towards you, Monsieur, is a result of the feelings with which your magnanimity, and the high-spirited and noble manner in which you have defended your country, have inspired me. I am acquainted with the details of your residence in Pisa, and with this among the rest, that you gained the esteem of all those who had opportunities of intercourse with you. That is the reward of virtue, in whatever situation it may find itself; be assured that I shall always entertain the liveliest sympathy for yours. "The motive of your journey to England, was a natural consequence of your sentiments with regard to your country. Nothing is wanting to your good cause but favourable circumstances. The natural interests of our empire, connected as they are with those of Great Britain; the mutual friendship between the two nations which results from this; the reception which my fleets have met with on the same account, and which my ships in the Mediterranean, and the commerce of Russia, would have to expect from a free people in friendly relations with my own, supply motives which cannot but be favourable to you. You may, therefore, be assured, Monsieur, that I shall not let slip the opportunities which will probably occur, of rendering you all the good services that political conjunctures may allow. "The Turks have declared against me the most unjust war that perhaps ever has been declared. At the present moment I am only able to defend myself. The blessing of Heaven, which has hitherto accompanied my cause, and which I pray God to continue to me, shows sufficiently that justice cannot be long suppressed, and that patience, hope, and courage, though the world is full of the most difficult situations, nevertheless attain their aim. I receive with
- 67. pleasure, Monsieur, the assurances of regard which you are pleased to express, and I beg you will be convinced of the esteem with which I am, "Catherine." Paoli had lived twenty long years an exile in London, when he was summoned back to his native country. The Corsicans sent him a deputation, and the French National Assembly, in a pompous address, invited him to return. On the 3d of April 1790, Paoli came for the first time to Paris. He was fêted here as the Washington of Europe, and Lafayette was constantly at his side. The National Assembly received him with stormy acclamations, and elaborate oratory. His reply was as follows: — "Messieurs, this is the fairest and happiest day of my life. I have spent my years in striving after liberty, and I find here its noblest spectacle. I left my country in slavery, I find it now in freedom. What more remains for me to desire? After an absence of twenty years, I know not what alterations tyranny may have produced among my countrymen; ah! it cannot have been otherwise than fatal, for oppression demoralizes. But in removing, as you have done, the chains from the Corsicans, you have restored to them their ancient virtue. Now that I am returning to my native country, you need entertain no doubts as to the nature of my sentiments. You have been magnanimous towards me, and I was never a slave. My past conduct, which you have honoured with your approval, is the pledge of my future course of action: my whole life, I may say, has been an unbroken oath to liberty; it seems, therefore, as if I had already sworn allegiance to the constitution which you have established; but it still remains for me to give my oath to the nation which adopts me, and to the monarch whom I now acknowledge. This is the favour which I desire of the august Assembly." In the club of the Friends of the Constitution, Robespierre thus addressed Paoli: "Ah! there was a time when we sought to crush
- 68. freedom in its last retreats. Yet no! that was the crime of despotism —the French people have wiped away the stain. What ample atonement to conquered Corsica, and injured mankind! Noble citizens, you defended liberty at a time when I did not so much as venture to hope for it. You have suffered for liberty; you now triumph with it, and your triumph is ours. Let us unite to preserve it for ever, and may its base opponents turn pale with fear at the sight of our sacred league." Paoli had no foreboding of the position into which the course of events was yet to bring him, in relation to this same France, or that he was once more to stand opposed to her as a foe. He left for Corsica. In Marseilles he was again received by a Corsican deputation, with the members of which came the two young club- leaders of Ajaccio—Joseph and Napoleon Bonaparte. Paoli wept as he landed on Cape Corso and kissed the soil of his native country; he was conducted in triumph from canton to canton; and the Te Deum was sung throughout the island. Paoli, as President of the Assembly, and Lieutenant-general of the Corsican National Guard, now devoted himself entirely to the affairs of his country; in the year 1791 he also undertook the command of the Division, and of the island. Although the French Revolution had silenced the special interests of the Corsicans, they began again to demand attention, and this was particularly felt by Paoli, among whose virtues patriotism was always uppermost. Paoli could never transform himself into a Frenchman, or forget that his people had possessed independence, and its own constitution. A coolness sprang up between him and certain parties in the island; the aristocratic French party, namely, on the one hand, composed of such men as Gaffori, Rossi, Peretti, and Buttafuoco; and the extreme democrats on the other, who saw the welfare of the world nowhere but in the whirl of the French Revolution, such as the Bonapartes, Saliceti, and Arenas. The execution of the king, and the wild and extravagant procedure of the popular leaders in Paris, shocked the philanthropic Paoli. He
- 69. gradually broke with France, and the rupture became manifest after the unsuccessful French expedition from Corsica against Sardinia, the failure of which was attributed to Paoli. His opponents had lodged a formal accusation against him and Pozzo di Borgo, the Procurator-general, libelling them as Particularists, who wished to separate the island from France. The Convention summoned him to appear before its bar and answer the accusations, and sent Saliceti, Lacombe, and Delcher, as commissaries to the island. Paoli, however, refused to obey the decree, and sent a dignified and firm address to the Convention, in which he repelled the imputations made upon him, and complained of their forcing a judicial investigation upon an aged man, and a martyr for freedom. Was a Paoli to stand in a court composed of windy declaimers and play-actors, and then lay his head, grown gray in heroism, beneath the knife of the guillotine? Was this to be the end of a life that had produced such noble fruits? The result of this refusal to obey the orders of the Convention, was the complete revolt of Paoli and the Paolists from France. The patriots prepared for a struggle, and published such enactments as plainly intimated that they wished Corsica to be considered as separated from France. The commissaries hastened home to Paris; and after receiving their report, the Convention declared Paoli guilty of high treason, and placed him beyond the protection of the law. The island was split into two hostile camps, the patriots and the republicans, and already fighting had commenced. Meanwhile Paoli had formed the plan of placing the island under the protection of the English Government. No course lay nearer or was more natural than this. He had already entered into communication with Admiral Hood, who commanded the English fleet before Toulon, and now with his ships appeared on the Corsican coast. He landed near Fiorenzo on the 2d of February. This fortress fell after a severe bombardment; and the commandant of Bastia, General Antonio Gentili, capitulated. Calvi alone, which had withstood in previous centuries so many assaults, still held out, though the English bombs
- 70. made frightful havoc in the little town, and all but reduced it to a heap of ruins. At length, on the 20th of July 1794, the fortress surrendered; the commandant, Casabianca, capitulated, and embarked with his troops for France. As Bonifazio and Ajaccio were already in the hands of the Paolists, the Republicans could no longer maintain a footing on the island. They emigrated, and Paoli and the English remained undisputed masters of Corsica. A general assembly now declared the island completely severed from France, and placed it under the protection of England. England, however, did not content herself with a mere right of protection—she claimed the sovereignty of Corsica; and this became the occasion of a rupture between Paoli and Pozzo di Borgo, whom Sir Gilbert Elliot had won for the English side. On the 10th of June 1794, the Corsicans declared that they would unite their country to Great Britain; that it was, however, to remain independent, and be governed by a viceroy according to its own constitution. Paoli had counted on the English king's naming him viceroy; but he was deceived, for Gilbert Elliot was sent to Corsica in this capacity—a serious blunder, since Elliot was totally unacquainted with the condition of the island, and his appointment could not but deeply wound Paoli. The gray-haired man immediately withdrew into private life; and as Elliot saw that his relation to the English, already unpleasant, must soon become dangerous, he wrote to George III. that the removal of Pasquale was desirable. This was accomplished. The King of England, in a friendly letter, invited Paoli to come to London, and spend his remaining days in honour at the court. Paoli was in his own house at Morosaglia when he received the letter. Sadly he now proceeded to San Fiorenzo, where he embarked, and left his country for the third and last time, in October 1795. The great man shared the same fate as most of the legislators and popular leaders of antiquity; he died rewarded with ingratitude, unhappy, and in exile. The two greatest men of Corsica, Pasquale and Napoleon, foes to
- 71. each other, were both to end their days and be buried on British territory. The English government of Corsica—from ignorance of the country very badly conducted—lasted only a short time. As soon as Napoleon found himself victorious in Italy, he despatched Generals Gentili and Casalta with troops to the island; and scarcely had they made their appearance, when the Corsicans, imbittered by the banishment of Paoli and their other grievances, rose against the English. In almost inexplicable haste they relinquished the island, from whose people they were separated by wide and ineradicable differences in national character; and by November 1796, not a single Englishman remained in Corsica. The island was now again under the supremacy of France. Pasquale Paoli lived to see Napoleon Emperor. Fate granted him at least the satisfaction of seeing a countryman of his own the most prominent and the most powerful actor in European history. After passing twelve years more of exile in London, he died peacefully on the 5th of February 1807, at the age of eighty-two, his mind to the last occupied with thoughts of the people whom he had so warmly loved. He was the patriarch and oldest legislator of European liberty. In his last letter to his friend Padovani, the noble old man, reviewing his life, says humbly:— "I have lived long enough; and if it were granted me to begin my life anew, I should reject the gift, unless it were accompanied with the intelligent cognisance of my past life, that I might repair the errors and follies by which it has been marked." One of the Corsican exiles announced his death to his countrymen in the following letter:— GIACOMORSI TO SIGNOR PADOVANI. "London, July 2, 1807. "It is, alas! true that the newspapers were correctly informed when they published the death of the poor General. He fell ill on Monday
- 72. the 2d of February, about half-past eight in the evening, and at half- past eleven on the night of Thursday he died in my arms. He leaves to the University at Corte salaries of fifty pounds a year each, for four professors; and another mastership for the School of Rostino, which is to be founded in Morosaglia. "On the 13th of February, he was buried in St. Pancras, where almost all Catholics are interred. His funeral will have cost nearly five hundred pounds. About the middle of last April, I and Dr. Barnabi went to Westminster Abbey to find a spot where we shall erect a monument to him with his bust. "Paoli said when dying:—My nephews have little to hope for; but I shall bequeath to them, for their consolation, and as something to remember me by, this saying from the Bible—'I have been young, and now am old, yet have I not seen the righteous forsaken, nor his seed begging bread.'" CHAPTER IX. PAOLI'S BIRTHPLACE. It was late when I reached Rostino, or Morosaglia. Under this name is understood, not a single paese, but a number of villages scattered among the rude, stern hills. I found my way with difficulty through these little neighbour hamlets to the convent of Morosaglia, climbing rough paths over rocks, and again descending under gigantic chestnuts. A locanda stands opposite the convent, a rare phenomenon in the country districts of Corsica. I found there a lively and intelligent young man, who informed me he was director of the Paoli School, and promised me his assistance for the following day. In the morning, I went to the little village of Stretta, where the three Paolis were born. One must see this Casa Paoli in order rightly to comprehend the history of the Corsicans, and award a just admiration to these singular men. The house is a very wretched, black, village-cabin, standing on a granite rock; a brooklet runs
- 73. immediately past the door; it is a rude structure of stone, with narrow apertures in the walls, such as are seen in towers; the windows few, unsymmetrically disposed, unglazed, with wooden shutters, as in the time of Pasquale. When the Corsicans had elected him their general, and he was expected home from Naples, Clemens had glass put in the windows of the sitting-room, in order to make the parental abode somewhat more comfortable for his brother. But Paoli had no sooner entered and remarked the luxurious alteration, than he broke every pane with his stick, saying that he did not mean to live in his father's house like a Duke, but like a born Corsican. The windows still remain without glass; the eye overlooks from them the magnificent panorama of the mountains of Niolo, as far as the towering Monte Rotondo. A relative of Paoli's—a simple country girl of the Tommasi family— took me into the house. Everything in it wears the stamp of humble peasant life. You mount a steep wooden stair to the mean rooms, in which Paoli's wooden table and wooden seat still stand. With joy, I saw myself in the little chamber in which Pasquale was born; my emotions on this spot were more lively and more agreeable than in the birth-chamber of Napoleon. Once more that fine face, with its classic, grave, and dignified features, rose before me, and along with it the forms of a noble father and a heroic brother. In this little room Pasquale came to the world in April of the year 1724. His mother was Dionisia Valentina, an excellent woman from a village near Ponte Nuovo—the spot so fatal to her son. His father, Hyacinth, we know already. He had been a physician, and became general of the Corsicans along with Ceccaldi and Giafferi. He was distinguished by exalted virtues, and was worthy of the renown that attaches to his name as the father of two such sons. Hyacinth had great oratorical powers, and some reputation as a poet. Amid the din of arms those powerful spirits had still time and genial force enough to rise free above the actual circumstances of their condition, and sing war-hymns, like Tyrtæus.
- 74. Here is a sonnet addressed by Hyacinth to the brave Giafferi, after the battle of Borgo:— "To crown unconquer'd Cyrnus' hero-son, See death descend, and destiny bend low; Vanquish'd Ligurians, by their sighs of wo, Swelling fame's trumpet with a louder tone. Scarce was the passage of the Golo won, Than in their fort of strength he storm'd the foe. Perils, superior numbers scorning so, Vict'ry still follow'd where his arms had shone. Chosen by Cyrnus, fate the choice approved, Trusting the mighty conflict to his sword, Which Europe rose to watch, and watching stands. By that sword's flash, e'en fate itself is moved; Thankless Liguria has its stroke deplored, While Cyrnus takes her sceptre from his hands." Such men are as if moulded of Greek bronze. They are the men of Plutarch, and resemble Aristides, Epaminondas, and Timoleon. They could resign themselves to privation, and sacrifice their interests and their lives; they were simple, sincere, stout-hearted citizens of their country. They had become great by facts, not by theories, and the high nobility of their principles had a basis, positive and real, in their actions and experiences. If we are to express the entire nature of these men in one word, that word is Virtue, and they were worthy of virtue's fairest reward—Freedom. My glance falls upon the portrait of Pasquale. I could not wish to imagine him otherwise. His head is large and regular; his brow arched and high, the hair long and flowing; his eyebrows bushy, falling a little down into the eyes, as if swift to contract and frown; but the blue eyes are luminous, large, and free—full of clear,
- 75. perceptive intellect; and an air of gentleness, dignity, and benevolence, pervades the beardless, open countenance. One of my greatest pleasures is to look at portraits and busts of great men. Four periods of these attract and reward our examination most—the heads of Greece; the Roman heads; the heads of the great fifteenth and sixteenth centuries; and the heads of the eighteenth century. It would be an almost endless labour to arrange by themselves the busts of the great men of the eighteenth century; but such a Museum would richly reward the trouble. When I see a certain group of these together, it seems to me as if I recognised a family resemblance prevailing in it—a resemblance arising from the presence in each, of one and the same spiritual principle—Pasquale, Washington, Franklin, Vico, Genovesi, Filangieri, Herder, Pestalozzi, Lessing. Pasquale's head is strikingly like that of Alfieri. Although the latter, like Byron, aristocratic, proud, and unbendingly egotistic, widely differs in many respects from his contemporary, Pasquale—the peaceful, philanthrophic citizen; he had nevertheless a soul full of a marvellous energy, and burning with the hatred of tyranny. He could understand such a nature as Paoli's better than Frederick the Great. Frederick once sent to this house a present for Paoli—a sword bearing the inscription, Libertas, Patria. Away in distant Prussia, the great king took Pasquale for an unusually able soldier. He was no soldier; his brother Clemens was his sword; he was the thinking head—a citizen and a strong and high-hearted man. Alfieri comprehended him better, he dedicated his Timoleon to him, and sent him the poem with this letter:— TO SIGNOR PASQUALE PAOLI, THE NOBLE DEFENDER OF CORSICA. "To write tragedies on the subject of liberty, in the language of a country which does not possess liberty, will perhaps, with justice, appear mere folly to those who look no further than the present. But he who draws conclusions for the future from the constant vicissitudes of the past, cannot pronounce such a rash judgment. I therefore dedicate this my tragedy to you, as one of the enlightened few—one
- 76. who, because he can form the most correct idea of other times, other nations, and high principles—is also worthy to have been born and to have been active in a less effeminate century than ours. Although it has not been permitted you to give your country its freedom, I do not, as the mob is wont to do, judge of men according to their success, but according to their actions, and hold you entirely worthy to listen to the sentiments of Timoleon, as sentiments which you are thoroughly able to understand, and with which you can sympathize. Vittoria Alfieri." Alfieri inscribed on the copy of his tragedy which he sent to Pasquale, the following verses:— "To Paoli, the noble Corsican Who made himself the teacher and the friend Of the young France. Thou with the sword hast tried, I with the pen, In vain to rouse our Italy from slumber. Now read; perchance my hand interprets rightly The meaning of thy heart." Alfieri exhibited much delicacy of perception in dedicating the Timoleon to Paoli—the tragedy of a republican, who had once, in the neighbouring Sicily, given wise democratic laws to a liberated people, and then died as a private citizen. Plutarch was a favourite author with Paoli, as with most of the great men of the eighteenth century, and Epaminondas was his favourite hero; the two were kindred natures—both despised pomp and expensive living, and did not imagine that their patriotic services and endeavours were incompatible with the outward style of citizens and commoners. Pasquale was fond of reading: he had a choice library, and his memory was retentive. An old man told me that once, when as a boy he was walking along the road with a school-fellow, and reciting a passage from Virgil, Paoli accidentally came up behind him,
- 77. slapped him on the shoulder, and proceeded himself with the passage. Many particulars of Paoli's habits are still remembered by the people here. The old men have seen him walking about under these chestnuts, in a long green, gold-laced coat,[N] and a vest of brown Corsican cloth. When he showed himself, he was always surrounded by his peasantry, whom he treated as equals. He was accessible to all, and he maintained a lively recollection of an occasion when he had deeply to repent his having shut himself up for an hour. It was one day during the last struggle for independence; he was in Sollacaro, embarrassed with an accumulation of business, and had ordered the sentry to allow no one admission. After some time a woman appeared, accompanied by an armed youth. The woman was in mourning, wrapped in the faldetta, and wore round her neck a black ribbon, to which a Moor's head, in silver—the Corsican arms— was attached. She attempted to enter—the sentry repelled her. Paoli, hearing a noise, opened the door, and demanded hastily and imperiously what she wanted. The woman said with mournful calmness: "Signor, be so good as listen to me. I was the mother of two sons; the one fell at the Tower of Girolata; the other stands here. I come to give him to his country, that he may supply the place of his dead brother." She turned to the youth, and said to him: "My son, do not forget that you are more your country's child than mine." The woman went away. Paoli stood a moment as if thunderstruck; then he sprang after her, embraced with emotion mother and son, and introduced them to his officers. Paoli said afterwards that he never felt so embarrassed as before that noble- hearted woman. He never married; his people were his family. His only niece, the daughter of his brother Clemens, was married to a Corsican called Barbaggi. But Paoli himself, capable of all the virtues of friendship, was not without a noble female friend, a woman of talent and glowing patriotism, to whom the greatest men of the country confided their political ideas and plans. This Corsican Roland,
- 78. however, kept no salon; she was a nun, of the noble house of Rivarola. A single circumstance evinces the ardent sympathy of this nun for the patriotic struggles of her countrymen; after Achille Murati's bold conquest of Capraja, she herself, in her exultation at the success of the enterprise, went over to the island, as if to take possession of it in the name of Paoli. Many of Pasquale's letters are addressed to the Signora Monaca, and are altogether occupied with politics, as if they had been written to a man. The incredible activity of Paoli appears from his collected letters. The talented Italian Tommaseo (at present living in exile in Corfu) has published a large volume containing the most important of these. They are highly interesting, and exhibit a manly, vigorous, and clear intellect. Paoli disliked writing—he dictated, like Napoleon; he could not sit long, his continually active mind allowed him no rest. It is said of him that he never knew the date; that he could read the future, and that he frequently had visions. Paoli's memory is very sacred with his people. Napoleon elates the soul of the Corsican with pride, because he was his brother; but when you name the name of Paoli, his eye brightens like that of a son, at the mention of a noble departed father. It is impossible for a man to be more loved and honoured by a whole nation after his death than Pasquale Paoli; and if posthumous fame is a second life, then Corsica's and Italy's greatest man of the eighteenth century lives a thousandfold—yes, lives in every Corsican heart, from the tottering graybeard who knew him in his youth, to the child on whose soul his high example is impressed. No greater name can be given to a man than "Father of his country." Flattery has often abused it and made it ridiculous; among the Corsicans I saw that it could also be applied with truth and justice. Paoli contrasts with Napoleon, as philanthropy with self-love. No curses of the dead rise to execrate his name. At the nod of Napoleon, millions of human beings were murdered for the sake of fame and power. The blood that Paoli shed, flowed for freedom, and
- 79. his country gave it freely as that mother-bird that wounds her breast to give her fainting brood to drink. No battle-field makes Paoli's name illustrious; but his memory is here honoured by the foundation-school of Morosaglia, and this fame seems to me more human and more beautiful than the fame of Marengo or the Pyramids. I visited this school, the bequest of the noble patriot. The old convent supplies an edifice. It consists of two classes; the lower containing one hundred and fifty scholars, the upper about forty. But two teachers are insufficient for the large number of pupils. The rector of the lower class was so friendly as to hold a little examination in my presence. I here again remarked the naïveté of the Corsican character, as displayed by the boys. There were upwards of a hundred, between the ages of six and fourteen, separated into divisions, wild, brown little fellows, tattered and torn, unwashed, all with their caps on their heads. Some wore crosses of honour suspended on red ribbons; and these looked comical enough on the breasts of the little brown rascals—sitting, perhaps, with their heads supported between their two fists, and staring, frank and free, with their black eyes at all within range—proud, probably, of being Paoli scholars. These honours are distributed every Saturday, and worn by the pupil for a week; a silly, and at the same time, hurtful French practice, which tends to encourage bad passions, and to drive the Corsican—in whom nature has already implanted an unusual thirst for distinction—even in his boyhood, to a false ambition. These young Spartans were reading Telemachus. On my requesting the rector to allow them to translate the French into Italian, that I might see how they were at home in their mother- tongue, he excused himself with the express prohibition of the Government, which "does not permit Italian in the schools." The branches taught were writing, reading, arithmetic, and the elements of geography and biblical history. The schoolroom of the lower class is the chapter-hall of the old convent in which Clemens Paoli dreamed away the closing days of
- 80. his life. Such a spacious, airy Aula as that in which these Corsican youngsters pursue their studies, with the view from its windows of the mighty hills of Niolo, and the battle-fields of their sires, would be an improvement in many a German university. The heroic grandeur of external nature in Corsica seems to me to form, along with the recollections of their past history, the great source of cultivation for the Corsican people; and there is no little importance in the glance which that Corsican boy is now fixing on the portrait yonder on the wall—for it is the portrait of Pasquale Paoli. CHAPTER X. CLEMENS PAOLI. "Blessed be the Lord my strength, who teacheth my hands to war, and my fingers to fight."—Psalm cxliv. The convent of Morosaglia is perhaps the most venerable monument of Corsican history. The hoary structure as it stands there, brown and gloomy, with the tall, frowning pile of its campanile by its side, seems itself a tradition in stone. It was formerly a Franciscan cloister. Here, frequently, the Corsican parliaments were held. Here Pasquale had his rooms, his bureaus, and often, during the summer, he was to be seen among the monks—who, when the time came, did not shrink from carrying the crucifix into the fight, at the head of their countrymen. The same convent was also a favourite residence of his brave brother Clemens, and he died here, in one of the cells, in the year 1793. Clemens Paoli is a highly remarkable character. He resembles one of the Maccabees, or a crusader glowing with religious fervour. He was the eldest son of Hyacinth. He had served with distinction as a soldier in Naples; then he was made one of the generals of the Corsicans. But state affairs did not accord with his enthusiastic turn
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