Introduction to DBMS Purpose of Database System Views

Introduction to DBMS Purpose of Database System Views of data Data Models Database Languages Database System Architecture Database users and Administrator

Database Management System (DBMS) Collection of interrelated data Set of programs to access the data DMBS contains information about a particular enterprise DBMS provides an environment that it both convenient and efficient to use

Purpose of Database Systems Database management systems were developed to handle the following difficulties of typical fileprocessing systems supported by conventional operating systems: Data redundancy and inconsistency Difficulty in accessing data Data isolation – multiple files and formats Integrity problems Atomicity of updates Concurrent access by multiple users Security problems

DATABASE APPLICATIONS Banking: all transactions Airlines: reservations, schedules Universities: registration, grades Sales: customers, products, purchases Online retailers: order tracking, customized recommendations Manufacturing: production, inventory, orders, supply chain Human resources: employee records, salaries, tax deductions

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 customer_id : string; customer_name : string; customer_street : string; customer_city : string; end; View level: application programs hide details of data types. Views can also hide information (such as an employee’s salary) for security purposes.

Views of Data An architecture for a database system View level View 1 View 2 … Logical level Physical level View n

Instances and Schemas Similar to types and variables in programming languages Schema – the logical structure of the database Example: 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.

Data Models A collection of tools for describing Data relationships Data semantics Data constraints Relational model Entity-Relationship data model (mainly for database design) Object-based data models (Object-oriented and Object-relational) Semi structured data model (XML) Other older models: Network model Hierarchical model

Database Languages Data Definition Language • Specification notation for defining the database schema • DDL compiler generates a set of tables stored in a data dictionary • Data dictionary contains metadata (data about data) • Data storage and definition language – special type of DDL in which the storage structure and access methods used by the database system are specified

Data Definition Language-DDL • Data Definition Language (DDL) statements are used to define the database structure or schema. Some examples: • CREATE - to create objects in the database • ALTER - alters the structure of the database • DROP - delete objects from the database TRUNCATE - remove all records from a table, including all spaces allocated for the records are removed • COMMENT - add comments to the data dictionary • RENAME - rename an object

Data Manipulation Language ( DML ) Language for accessing and manipulating the data organized by the appropriate data model 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

Data Manipulation Language (DML) • Data Manipulation Language (DML) statements are used for managing data within schema objects. Some examples: • • SELECT - Retrieve data from the a database INSERT - Insert data into a table UPDATE - Updates existing data within a table DELETE - deletes all records from a table, the space for the records remain MERGE - UPSERT operation (insert or update) CALL - Call a PL/SQL or Java subprogram EXPLAIN PLAN - explain access path to data LOCK TABLE - control concurrency

Data Control Language (DCL) statements. Some examples: GRANT - gives user's access privileges to database REVOKE - withdraw access privileges given with the GRANT command

Database System Architecture

Database Administrator(DBA) 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

Database Users • Users are differentiated by the way they expect to interact with the system. • Application programmers: interact with system through DML calls. • Specialized users: write specialized database applications that do not fit into the traditional data processing framework • Sophisticated users: form requests in a database query language. • Naive users: invoke one of the permanent application programs that have been written previously

THANK YOU BY: Ms. K. Gayathri, Assistant Professor, Dept of Computer Science, Bon Secours College for Women, Thanjavur.