Unit-1-Introduction.ppt for the gigachad
- 2. Basic Definitions Data: Known facts that can be recorded and have an implicit meaning. Database: A collection of related data. Database Management System (DBMS): Collection of programs that enables users to create and maintain a database. A software package/ system to facilitate the creation and maintenance of a computerized database.
- 3. Types of Databases and Database Applications Numeric and Textual Databases Multimedia Databases Geographic Information Systems (GIS) Data Warehouses Real-time and Active Databases
- 4. Drawbacks of using file system Data redundancy and inconsistency Data redundancy occurs when the same piece of data exists in multiple places, whereas data inconsistency is when the same data exists in different formats in multiple tables. Difficulty in accessing data Need to write a new program to carry out each new task Integrity problems Integrity constraints - provide a way of ensuring that changes made to the database by authorized users do not result in a loss of data consistency. Hard to add new constraints or change existing ones
- 5. Drawbacks of using File system 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
- 6. Database System: The DBMS software and the database.
- 7. Characteristics of the Database Approach Self-describing nature of a database system: A DBMS catalog stores the description of the database. Which contains information such as the structure of each file, the type and storage format of each data item, and various constraints on the data. The description is called meta-data. This allows the DBMS software to work with different databases. Insulation between programs and data: Called program-data independence. Allows changing data storage structures and operations without having to change the DBMS access programs.
- 8. Characteristics of the Database Approach Data Abstraction: A data model is used to hide storage details and present the users with a conceptual view of the database. Support of multiple views of the data: Each user may see a different view of the database, which describes only the data of interest to that user. Sharing of data and multiuser transaction processing : Allowing a set of concurrent users to retrieve and to update the database. Concurrency control within the DBMS guarantees that each transaction is correctly executed or completely aborted. OLTP (Online Transaction Processing) is a major part of database applications.
- 9. Typical DBMS Functionality Define a database : in terms of data types, structures and constraints Construct or Load the Database on a secondary storage medium Manipulating the database : querying, generating reports, insertions, deletions and modifications to its content, Accessing the database through Web applications Concurrent Processing and Sharing by a set of users and programs – yet, keeping all data valid and consistent Slide 1-9
- 10. Example of a Database (with a Conceptual Data Model) Mini-world for the example: Part of a UNIVERSITY environment. Some mini-world entities: STUDENTs COURSEs SECTIONs (of COURSEs) (academic) DEPARTMENTs INSTRUCTORs Note: The above could be expressed in the ENTITY-RELATIONSHIP data model. Slide 1-11
- 11. Example of a Database (with a Conceptual Data Model) Some mini-world relationships: SECTIONs are of specific COURSEs STUDENTs take SECTIONs COURSEs have prerequisite COURSEs INSTRUCTORs teach SECTIONs COURSEs are offered by DEPARTMENTs STUDENTs major in DEPARTMENTs Note: The above could be expressed in the ENTITY-RELATIONSHIP data model. Slide 1-12
- 12. Database Users Users may be divided into those who actually use and control the content (called “Actors on the Scene”) and those who enable the database to be developed and the DBMS software to be designed and implemented (called “Workers Behind the Scene”). Slide 1-13
- 13. Database Users Actors on the scene Database administrators: responsible for authorizing access to the database, for coordinating and monitoring its use, acquiring software and hardware resources, controlling its use and monitoring efficiency of operations. Database Designers: responsible to define the content, the structure, the constraints, and functions or transactions against the database. They must communicate with the end- users and understand their needs. End-users: they use the data for queries, reports and some of them actually update the database content. Slide 1-14
- 14. Categories of End-users Casual : access database occasionally when needed Naive or Parametric : They make up a large section of the end-user population. They use previously well- defined functions in the form of “canned transactions” against the database. Examples are bank-tellers or reservation clerks who do this activity for an entire shift of operations. Slide 1-15
- 15. Categories of End-users Sophisticated : these include business analysts, scientists, engineers, others thoroughly familiar with the system capabilities. Many use tools in the form of software packages that work closely with the stored database. Stand-alone : mostly maintain personal databases using ready-to- use packaged applications. An example is a tax program user that creates his or her own internal database. Slide 1-16
- 16. Workers Behind the Scene DBMS system Designers and Implementers Design and implement the DBMS modules and interfaces as a software package. Tool Developers Design and implement tools Operators and Maintenance Personnel Responsible for the actual running and maintenance of the hardware and software environment for the database system. Slide 1-17
- 17. Advantages of Using the Database Approach Controlling redundancy Sharing of data among multiple users. Restricting unauthorized access to data. Providing backup and recovery services. Providing multiple interfaces to different classes of users. Representing complex relationships among data. Enforcing integrity constraints on the database. Slide 1-18
- 18. DBMS Software 1. Oracle 2. SQL server 3. IBM DB2 4. SAP Sybase ASE 5. Postgre SQL 6. MYSQL 7. Tera data 8. Informix 9. Ingres 10.MariaDB
- 19. Largest Databases in the World 1. The World Data Centre for Climate 2. National Energy Research Scientific computing Center 3. AT&T – Telecommunication 4. Google 5. Sprint – Telecommunication 6. Choice point 7. Youtube 8. Amazon 9. Central Intelligence Agency (CIA) 10. Library of Congress
- 20. When not to use a DBMS Main inhibitors (costs) of using a DBMS: High initial investment in hardware, software and training. Overhead for providing generality, security, concurrency control, recovery, and integrity functions. When a DBMS may be unnecessary: If the database and applications are simple, well defined, and not expected to change. If there are stringent real-time requirements that may not be met because of DBMS overhead. If access to data by multiple users is not required. Slide 1-21
- 21. When not to use a DBMS When no DBMS may suffice: If the database system is not able to handle the complexity of data because of modeling limitations If the database users need special operations not supported by the DBMS. Slide 1-22
- 22. Data Models Data Model: A collection of concepts to describe the structure of a database, the operations for manipulating these structures, and certain constraints that the database should obey. Data Model Structure and Constraints: Constructs are used to define the database structure Constructs typically include elements (and their data types) as well as groups of elements (e.g. entity, record, table), and relationships among such groups Constraints specify some restrictions on valid data; these constraints must be enforced at all times
- 23. Categories of Data Models Conceptual (high-level, semantic) data models: Provide concepts that are close to the way many users perceive data. (Also called entity-based or object-based data models.) Physical (low-level, internal) data models: Provide concepts that describe details of how data is stored in the computer. These are usually specified through DBMS design and administration manuals Implementation (representational) data models: Provide concepts that fall between the above two, used by many commercial DBMS implementations (e.g. relational data models used in many commercial systems).
- 24. Schemas versus Instances Database Schema: The description of a database. Includes descriptions of the database structure, data types, and the constraints on the database. Slide 1-25
- 25. Database State: The data stored in a database at a particular moment in time. This includes the collection of all the data in the database. Refers to the content of a database at a moment in time. Also called database instance (or occurrence or snapshot). The term instance is also applied to individual database components, e.g. record instance, table instance, entity instance
- 26. Initial Database State: Refers to the database state when it is initially loaded into the system. Valid State: A state that satisfies the structure and constraints of the database. Distinction The database schema changes very infrequently. The database state changes every time the database is updated. Schema is also called intension. State is also called extension.
- 28. Three schema architecture Important characteristics of database approach: Insulation of programs and data Support multiple user views Use of a catalog to store the database description (Schema) An architecture of schema is proposed to achieve these characteristics Architecture goal: To separate the user application and the database
- 30. Three schema architecture Defines DBMS schemas at three levels: Internal schema at the internal level to describe physical storage structures and access paths. Typically uses a physical data model. Conceptual schema at the conceptual level to describe the structure and constraints for the whole database for a community of users. Uses a conceptual or an implementation data model. External schemas at the external level to describe the various user views. Usually uses the same data model as the conceptual level.
- 31. Data Independence Capacity to change the schema at one level of database system without having to change the schema at the next higher level Logical Data Independence: The capacity to change the conceptual schema without having to change the external schemas and their application programs. Physical Data Independence: The capacity to change the internal schema without having to change the conceptual schema.
- 33. Once the design of a database is completed and a DBMS is chosen to implement the database, the first order of the day is to specify conceptual and internal schemas for the database and any mappings between the two.
- 34. In many DBMS’s where no strict separation of levels is maintained, one language, called the data definition language (DDL), is used by the DBA and by database designers to define both schemas. This Language is used define data structures and specially database schemas. these statements are used to create, alter, or drop data structures. ALTER ,CREATE ,DROP are some examples of DDL.
- 35. The DBMS will have a DDL compiler whose function is to process DDL statements in order to identify descriptions of the schema constructs and to store the schema description in the DBMS catalog.
- 36. In DBMSs where a clear separation is maintained between the conceptual and internal levels, the DDL is used to specify the conceptual schema only. Another language, the storage definition language (SDL), is used to specify the internal schema. This language is used to define internal schema. It defines that what will be the physical structure of database, how many bites per field will be used, what will be the order of fields, and how records will be accesses etc.
- 37. The mappings between the two schemas may be specified in either one of these languages. For a true three-schema architecture, we would need a third language, the view definition language (VDL), to specify user views and their mappings to the conceptual schema, but in most DBMS’s the DDL is used to define both conceptual and external schemas.
- 38. Once the database schemas are compiled and the database is populated with data, users must have some means to manipulate the database. Typical manipulations include retrieval, insertion, deletion, and modification of the data. The DBMS provides a data manipulation language (DML) for these purposes.
- 39. DBMSs, the preceding types of languages are usually not considered distinct languages; rather, a comprehensive integrated language is used that includes constructs for conceptual schema definition, view definition, and data manipulation
- 40. Storage definition is typically kept separate, since it is used for defining physical storage structures to fine-tune the performance of the database system, and it is usually utilized by the DBA staff
- 41. A typical example of a comprehensive database language is the SQL relational database language which represents a combination of DDL, VDL, and DML, as well as statements for constraint specification and schema evolution. The SDL was a component in earlier versions of SQL but has been removed from the language to keep it at the conceptual and external levels only.
- 42. There are two main types of DMLs. A high- level or nonprocedural DML can be used on its own to specify complex database operations in a concise manner. Many DBMSs allow high-level DML statements either to be entered interactively from a terminal (or monitor) or to be embedded in a general-purpose programming language.
- 43. In the latter case, DML statements must be identified within the program so that they can be extracted by a pre-compiler and processed by the DBMS. A low-level or procedural DML must be embedded in a general-purpose programming language.
- 44. Low-level DMLs are also called record-at-a- time DMLs because of this property. High-level DMLs, such as SQL, can specify and retrieve many records in a single DML statement and are hence called set-at-a-time or set-oriented DMLs. A query in a high-level DML often specifies which data to retrieve rather than how to retrieve it; hence, such languages are also called declarative
- 45. Whenever DML commands, whether high- level or low-level, are embedded in a general- purpose programming language, that language is called the host language and the DML is called the data sublanguage. On the other hand, a high-level DML used in a stand-alone interactive manner is called a query language.
- 46. User-friendly interfaces provided by a DBMS may include the following: Menu-Based Interfaces for Web Clients or Browsing. These interfaces present the user with lists of options (called menus) that lead the user through the formulation of a request. Forms-Based Interfaces. A forms-based interface displays a form to each user. Graphical User Interfaces. A GUI typically displays a schema to the user in diagrammatic form Natural Language Interfaces. These interfaces accept requests written in English or some other language and attempt to understand them. DBMS Interfaces
- 47. Interfaces for Parametric Users. Parametric users, such as bank tellers, often have a small set of operations that they must perform repeatedly. Interfaces for the DBA. Most database systems contain privileged commands that can be used only by the DBA staff. These include commands for creating accounts, setting system parameters, granting account authorization, changing a schema, and reorganizing the storage structures of a database.
- 49. A database system being a complex software system is partitioned into several software components that handle various tasks such as data definition and manipulation, security and data integrity, data recovery and concurrency control, and performance optimization
- 51. Data definition: DBMS provides functions to define the structure of the data. functions include defining and modifying the record structure, the data type of fields, and the various constraints to be satisfied by the data in each field. It is the responsibility of database administrator to define the database, and make changes to its definition (if required) using the DDL and other privileged commands. The DDL compiler component of DBMS processes these schema definitions, and stores the schema descriptions in the DBMS catalog (data dictionary). Other DBMS components then refer to the catalog information as and when required.
- 52. Data manipulation Once the data structure is defined, data needs to be manipulated. The manipulation of data includes insertion, deletion, and modification of records. The functions that perform these operations are also part of the DBMS.
- 53. The queries that are defined as a part of the application programs are known as planned queries. The application programs are submitted to a precompiler, which extracts DML commands from the application program and send them to DML compiler for compilation.
- 54. The rest of the program is sent to the host language compiler. The object codes of both the DML commands and the rest of the program are linked and sent to the query evaluation engine for execution.
- 55. The sudden queries that are executed as and when the need arises are known as unplanned queries (interactive queries). These queries are compiled by the query complier, and then optimized by the query optimizer. The query optimizer consults the data dictionary for statistical and other physical information about the stored data. (The optimized query is finally passed to the query evaluation engine for execution.
- 56. The naive users of the database can also query and update the database by using some already given application program interfaces. The object code of these queries is also passed to query evaluation engine for processing.
- 57. Data security and integrity: The DBMS contain functions, which handle the security and integrity of data stored in the database. Since these functions can be easily invoked by the application, the application programmer need not code these functions in the programs.
- 58. Concurrency and data recovery: The DBMS also contains some functions that deal with the concurrent access of records by multiple users and the recovery of data after a system failure
- 59. Performance optimization: The DBMS has a set of functions that optimize the performance of the queries by evaluating the different execution plans of a query and choosing the best among them.
- 67. Slide 1-69