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USER-ORIENTED DESCRIPTION OF A DATABASE MANAGEMENT SYSTEM CS 143 1 TWO TYPES OF DATABASES (1) STATIC DATABASE • Describes Entities existing in the system through their properties. • Describes Relationships existing between entities. • Basically “static”; changes in the entities properties and relationships require “protected” operations. (2) DYNAMIC DATABASE • Describes dynamic Entities and Relationships. • Usually constructed as “simulation systems”. • Dynamic behavior and commands are inherent to the system. CS 143 2 GENERAL USER ORIENTED DESCRIPTION OF DBMS • A Database Management System (DBMS) consists of: (1) Database (2) Data Definition Language (DDL) (3) Query Language (QL) (4) Data Manipulation Language (DML) (5) “System” CS 143 3 THE DATABASE • A Database may be defined as a collection of “related”, “stripped down”, “declarative” statements arranged in a tabular form. • Example Starting with the declarative statements: - John Smith is an employee earning $35,000/year. - Paula Jones is an employee earning $40,000/year. - Peters is an employee working in the toy department and earning $30,000/year. - Paula Jones is the manager of the toy department. - John Smith works in the toy department. - Peters works in the toy department. CS 143 4 SOME ACTUAL DATABASE INSTANCES - We would construct the following two databases: Employee Managers First Name Last Name Department Salary John Smith toy 35000 Paula Jones toy 40000 Peters toy 30000 Supervisor Supervisees Jones Smith Jones Peters CS 143 5 DATA DEFINITION LANGUAGE Permits users to state imperative commands that yield (upon execution) database Schemas and Instances. Example: (1) to create the schema EMPLOYEE: CREATE TABLE EMPLOYEE (fname: string, lname: string, department: string, salary: integer) (2) to create the instance of EMPLOYEE shown in slide 5 above: INSERT EMPLOYEE (<John, Smith, toy, 35000>, <Paula, Jones, toy, 45000>, <null, Peters, toy, 30000>) CS 143 6 QUERY LANGUAGE (QL) • QUERY LANGUAGE (QL) • Permits users to state queries against the database. • Example SELECT lname, salary FROM Employee WHERE salary > 35000 CS 143 7 DATA MANIPULATION LANGUAGE (DML) • Permits users to manipulate (i. e. to modify) the database. • Example ALTER TABLE employee ADD COLUMN ssn INTEGER N.B. The DDL and DML are often combined into a single language. CS 143 8 THE SYSTEM • The software and hardware which permit users to define, construct, query and modify the database. CS 143 9