1. RELATIONAL DATABASE MANAGEMENT SYSTEM - I Subject code : BCA-12 and PGDCA 1

2. Overview of DBMS Section A 2

3. Database Related information when placed in an organized form makes a database. Examples – Dictionary – Telephone Directory – Student record register – Address book Two approaches for storing data in computers- – File based approach – Database approach 3

4. Why do we need a database? Keep records of our: – Clients – Staff – Volunteers To keep a record of activities and interventions; Keep sales records; Develop reports; Perform research

5. File based Approach A group of files storing data of an organization. Each file is independent from one another. Each file contains and processes information for one specific function, such as accounting or inventory. Files are designed using programs written in programming languages such as COBOl,C,C++. File systems may use a storage device such as hard disk or CD-ROM etc and involve maintaining physical location of the files. 5

6. Database Approach A shared collection of logically related data, designed to meet the information needs of an organization. Database is a single, large repository of data, which can be used simultaneously by many departments and users. Characteristics of Database Shared Persistence Validity/Integrity/Correctness Security Consistency Non-redundancy Data Independence 6

7. Database Management System (DBMS) A software system that Allows users to define, create and maintain a database Provides controlled access to database DBMS provides an environment that is both convenient and efficient to use. Examples – Computerized Library systems – Online Examination Application form – Flight reservations systems 7

8. Database Applications: – Banking: all transactions – Airlines: reservations, schedules – Universities: registration, grades – Sales: customers, products, purchases – Manufacturing: production, inventory, orders, supply chain – Human resources: employee records, salaries, tax deductions Commercially available DBMS are – Dbase – FoxPro – IMS – Oracle 8

9. Purpose of Database System In the early days, database applications were built on top of file systems Drawbacks of using file systems to store data: – 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 9

10. Purpose of Database Systems (Cont.) 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 10

11. Major Components of Database System Data Hardware (Computer System) Software (DBMS) Users (Naïve,Online, Sophisticated users, Application Programmers, DBA) Procedures (Instructions) DATABASE DATA AND PROGRAMS DBMS APPLICATION PROGRAMMERSEND USERS 11

12. Advantages of DBMS Controlling Redundancy Integrity can be enforced Inconsistency can be avoided Data can be shared Standards can be enforced Restricting unauthorized access Providing Backup and recovery 12

13. Disadvantages of DBMS Complexity Size Performance Higher impact of failure Cost of DBMS Additional Hardware costs 13

14. Architecture of DBMS The American National Standards Institute (ANSI) Standards Planning and Requirements Committee (SPARC) proposed a three layer model for DBMS. 3 Levels of DBMS are:- – External Level – Conceptual Level – Internal Level This model was later known as ANSI SPARC architecture of DBMS. 14

15. Levels of DBMS External level or User View – Highest level of DBMS – Closest to the user – Concerned with the way data is viewed by individual users – Only those portions of the database that are of concern to the user or application program are included. – Same database can have different views for different users. – Each External view is described by means of a scheme called an external Schema. – The external schema consists of the definition of logical records and the relationships in external view. Note:-A schema/scheme is an outline or plan that describes the records and relationships existing in the view. 15

16. Conceptual level or Logical View Level of indirection between external and internal level. Describes what data are actually stored in the database and the relationship that exist among the data. Defined by Conceptual schema which describes all records and relationships included in the database. There is only one Conceptual Schema per database. Defined by DBA. 16

17. Internal level or Physical View Lowest level of Architecture Closest to physical Storage i.e. how data is stored in the database. Describes the data structures and Access methods to be used by the database. Expressed by Internal Schema which contains the definition of the stored record, the method of representing the data fields and the access aids used. Defined by DBA. 17

18. View of Data An architecture for a database system 18

19. 3 Level ANSI Sparc Architecture of DBMS END USER EXTERNAL VIEW A EXTERNAL VIEW B EXTERNAL/CONCEPTUAL MAPPING A EXTERNAL/CONCEPTUAL MAPPING B CONCEPTUAL VIEW CONCEPTUAL/INTERNAL MAPPING STORED DATABASE (INTERNAL VIEW) DBMS EXTERNAL LEVEL CONCEPTUAL LEVEL INTERNAL LEVEL 19

20. Mapping b/w Views External/Conceptual Mapping – Each external schema is related to conceptual schema by external /conceptual mapping – It gives the correspondence among records and relationships of external/conceptual views. Conceptual/Internal Mapping – Conceptual schema is related to Internal Schema by Conceptual / internal mapping – This enables the DBMS to find the actual record or combination of records in physical storage that constitute a logical record in conceptual schema. – Mapping b/w two levels specifies the method of deriving the conceptual record from physical database. 20

21. Data Abstraction Major purpose of DBMS is to provide an abstract view of data i.e. system hides certain details of how data is stored and maintained. Since many users are not computer trained complexity is hidden from them through several levels of abstraction. 3 levels of abstraction – Internal Level or Physical Level – Conceptual Level or Logical Level – External Level or View Level 21

22. 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. 22

23. Instances and Schemas Schema – the logical structure of the database or overall description 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 – Subschema: External view is defined by a subschema Instance – the actual content of the database at a particular point in time – Analogous to the value of a variable 23

24. DATA INDEPENDENCE Ability to modify schema definition in one level without effecting a schema definition in next higher level is Data Independence. 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. Logical Data Independence – indicates that conceptual schema can be changed without affecting existing external schema 24

25. Database Administrator(DBA) A person or group of persons responsible for overall control of database systems. Main responsibilities of DBA are: – Deciding the information content of the database – Deciding the storage structures and access strategy – Deciding authorization checks and validation procedures – Granting of authorization for data access – Defining a strategy for backup and recovery – Monitoring performance and responding to changes in requirements. 25

26. Data Dictionary A metadata (Data Dictionary) is the data about the data. Also known as system catalog. DD is used to control the database operation, data integrity and accuracy. Contains information regarding database Provides the name of the data element, its description and data structure in which it may be found. Provides great assistance in producing a report of where a data element is used in all programs that mention it. 26

27. Database Languages Data Definition Languages (DDL) – It is a language that allows the users to define data and their relationship to other types of data. – It is mainly used to create files, databases, data dictionary and tables within databases. Data Manipulation Languages (DML) – It is a language that provides a set of operations to support the basic data manipulation operations on the data held in the databases. – By manipulation we mean: to retrieve information stored in the database To insert new information in the database To delete unwanted information from the database To modify existing data in the database Data Control Language (DCL) – DCL helps to control access to data and the database using statements grant and revoke 27

28. Types of Database Systems On the basis of no. of users – Single user DBMS – Multi user DBMS On the basis of Site Location – Centralized DBMS – Parallel DBMS – Distributed DBMS – Client/Server DBMS 28

29. Data Models A model is a representation of reality,' real world’ objects and events, and their associations. An integrated collection of concepts for describing and manipulating – data – data relationships – data semantics – data constraints A data model comprises of 3 components – A structural part – A manipulative part – A set of integrity rules 29

30. Types of Data Models Basically data models fall into 3 broad categories – Object based Data Models Entity-Relationship model Object Oriented Model – Physical Data Model – Record based Data Model Hierarchical Model Network Model Relational Model 30

31. Entity-Relationship Model Example of schema in the entity-relationship model 31

32. 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 32

33. 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 South North South West North Palo Alto Rye Palo Alto Harrison Rye A-101 A-215 A-201 A-217 A-201 Attributes 33

34. A Sample Relational Database 34

35. 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 35

36. 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 36