UNIT-1.pptx discusses about introduction to dbms
- 1. DATA BASE MANAGEMENT SYSTEMS
- 2. Unit 1: INTRODUCTION UNIT-I: An Overview of Database Management Introduction- What is Database System-What is Database-Why Database- Data Independence- Relation Systems and Others- Summary, Database system architecture Introduction- The Three Levels of Architecture-The External Level- the Conceptual Level- the Internal Level- Mapping- the Database Administrator-The Database Management Systems- Client/Server Architecture.
- 3. Unit 1: INTRODUCTION •Database system, Characteristics •Database Users •Database applications. •Brief introduction of different Data Models; •Concepts of Schema, Instance and data independence; •Three tier schema architecture for data independence; • Database system structure, •Centralized and Client Server architecture for the database.
- 4. Basic concepts Data : Collection of raw facts related to thing or place or event Ex: working hrs, salaries,wages Information : processed data or regular arrangement of data Ex: Emp daily working hrs, Accountant monthly salries Data base : collection of related information Ex: Bank database, college infon database etc DBMS : commercial software to collect ,store, manipulate the data in the database • DBMS contains information about a particular enterprise • DBMS provides an environment that is both convenient and efficient to use.
- 5. Commercial “off-the-shelf” (COTS): Oracle IBM DB2 (IBM) SQL Server (Microsoft) Sybase Informix (IBM) Access (Microsoft) Cache (Intersystems – nonrelational) Open Source: MySQL PostgreSQL
- 6. Database system, Characteristics • In the early days, database applications were built on top of file systems • Drawbacks of using file systems – Data redundancy and inconsistency • Multiple file formats, duplication of information in different files – Difficulty in accessing data • Need to write a new program to carry out each new task – Data isolation — multiple files and formats – Integrity problems • Integrity constraints (e.g. account balance > 0) become part of program code • Hard to add new constraints or change existing ones
- 7. Database system, Characteristics • Drawbacks of using file systems (cont.) – Atomicity of updates • Failures may leave database in an inconsistent state with partial updates carried out • E.g. transfer of funds from one account to another should either complete or not happen at all – Concurrent access by multiple users • Concurrent accessed needed for performance • Uncontrolled concurrent accesses can lead to inconsistencies – E.g. two people reading a balance and updating it at the same time – Security problems • Database systems offer solutions to all the above problems
- 8. Database applications NoteAnywhere there is data, there could be a database: Banking - accounts, loans, customers Airlines - reservations, schedules Universities - registration, grades Sales - customers, products, purchases Manufacturing - production, inventory, orders, supply chain Human resources - employee records, salaries, tax deductions Course context is an “enterprise” that has requirements for: Storage and management of 100’s of gigabytes or terabytes of data Support for 100’s or more of concurrent users and transactions Traditional supporting platform, e.g, Dell PowerEdge R720xd, 68 processors, 16GB RAM each, 50TB of disk space
- 9. Database Administrator • Coordinates all the activities of the database system; the database administrator has a good understanding of the enterprise’s information resources and needs. • Database administrator's duties include: – Schema definition – Storage structure and access method definition – Schema and physical organization modification – Granting user authority to access the database – Specifying integrity constraints – Monitoring performance and responding to changes in requirements
- 10. Database Users • Users are differentiated by the way they expect to interact with the system • Application programmers – interact with system through DML calls • Sophisticated users – form requests in a database query language • Specialized users – write specialized database applications that do not fit into the traditional data processing framework • Naïve users – invoke one of the permanent application programs that have been written previously – E.g. people accessing database over the web, bank tellers, clerical staff
- 11. Brief introduction of different Data Models • A collection of tools for describing – data – data relationships – data semantics – data constraints • Entity-Relationship model • Relational model • Other models: – object-oriented model – semi-structured data models – Older models: network model and hierarchical model
- 12. Entity Relationship Model (Cont.) • E-R model of real world – Entities (objects) • E.g. customers, accounts, bank branch – Relationships between entities • E.g. Account A-101 is held by customer Johnson • Relationship set depositor associates customers with accounts • Widely used for database design – Database design in E-R model usually converted to design in the relational model (coming up next) which is used for storage and processing
- 13. Entity-Relationship Model Example of schema in the entity-relationship model
- 14. Relational Model • Example of tabular data in the relational model customer- name Customer- id customer- street customer- city account- number Johnson Smith Johnson Jones Smith 192-83-7465 019-28-3746 192-83-7465 321-12-3123 019-28-3746 Alma North Alma Main North Palo Alto Rye Palo Alto Harrison Rye A-101 A-215 A-201 A-217 A-201 Attributes
- 15. A Sample Relational Database
- 18. Instances and Schemas • Similar to types and variables in programming languages • Schema – the logical structure of the database – e.g., the database consists of information about a set of customers and accounts and the relationship between them) – Analogous to type information of a variable in a program – Physical schema: database design at the physical level – Logical schema: database design at the logical level • Instance – the actual content of the database at a particular point in time – Analogous to the value of a variable • Physical Data Independence – the ability to modify the physical schema without changing the logical schema – Applications depend on the logical schema – In general, the interfaces between the various levels and components should be well defined so that changes in some parts do not seriously influence others.
- 19. View of Data (or)Three tier schema architecture for data independence;
- 20. Levels of Abstraction • Physical level describes how a record (e.g., customer) is stored. • Logical level: describes data stored in database, and the relationships among the data. type customer = record name : string; street : string; city : integer; end; • View level: application programs hide details of data types. Views can also hide information (e.g., salary) for security purposes.
- 22. Data Definition Language (DDL) • Specification notation for defining the database schema – E.g. create table account ( account-number char(10), balance integer) • DDL compiler generates a set of tables stored in a data dictionary • Data dictionary contains metadata (i.e., data about data) – database schema – Data storage and definition language • language in which the storage structure and access methods used by the database system are specified • Usually an extension of the data definition language
- 23. Data Manipulation Language (DML) • Language for accessing and manipulating the data organized by the appropriate data model – DML also known as query language • Two classes of languages – Procedural – user specifies what data is required and how to get those data – Nonprocedural – user specifies what data is required without specifying how to get those data • SQL is the most widely used query language
- 24. Transaction Management • A transaction is a collection of operations that performs a single logical function in a database application • Transaction-management component ensures that the database remains in a consistent (correct) state despite system failures (e.g., power failures and operating system crashes) and transaction failures. • Concurrency-control manager controls the interaction among the concurrent transactions, to ensure the consistency of the database.
- 25. Storage Management • Storage manager is a program module that provides the interface between the low-level data stored in the database and the application programs and queries submitted to the system. • The storage manager is responsible to the following tasks: – interaction with the file manager – efficient storing, retrieving and updating of data
- 26. Application Architectures Two-tier architecture: E.g. client programs using ODBC/JDBC to communicate with a database Three-tier architecture: E.g. web-based applications, and applications built using “middleware”