CS370 Spring 2007 CS 370 Database Systems Lecture 2 Overview of Database Systems

CS370 Spring 2007 Database Management System A DBMS is computer software with capability to store in an integrated structured format and enable the user to retrieve, manipulate and manage the data –Example: MS Access

CS370 Spring 2007 Why Do We need DBMS? Information is one of the most important assets of any organization. To be useful, the information must be: –Complete –Accurate –Available –Relevant Some information requirements are known in advance. Other requirements arise to meet a changing environment. Some requirements are necessary only one time.

CS370 Spring 2007 Where Do We need DBMS? Business national defense Engineering Medicine Law and on and on and on!

CS370 Spring 2007 What Came Before DBMS? Traditionally, there were file processing systems. Data was stored in sequential file, called a flat-file. Application programs were written for each requirement. Data was stored in records in a file that were written to, and read from, as needed. To provide the various facilities to different types of users, a DBMS –normally provides one or more specialized programming languages often called Database Languages.

CS370 Spring 2007 Database Languages Data Description Languages (DDL) –It is used to define field’s records, and relationship among different types of records Data Manipulation Languages (DML) –It is used to store and retrieve data in the database –Two classes 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 Control Language (DCL) –It is responsible for the data security

CS370 Spring 2007 DBMS System Programmers write application programs either in separate languages or in the DBMS language File are accessed through the DBMS The DBMS controls all processing, storage, retrieval, generation, and physical access function APPLICATION PROGRAM DBMS FILE

CS370 Spring 2007 Components of DBMS Hardware: Can range from a PC to a network of computers. Software: DBMS, operating system, network software (if necessary) and also the application programs. Data: Used by the organization and a description of this data called the schema. Procedures: Instructions and rules that should be applied to the design and use of the database and DBMS. People: Users Database system involves five major components namely

CS370 Spring 2007 Characteristics of a DBMS It is a computerized record-keeping system. It contains facilities that allow the user to... –Add and delete files to the system –Insert, retrieve, update, and delete data in existing files It is collection of databases –A DBMS may contain many databases that can be used for separate purposes or combined to provide useful information

CS370 Spring 2007 Functions of A DBMS To store data To organize data To control access to data To protect data To summarise, a database system consists of :- A database (data) A DBMS (software) A DDL & DML (part of a DBMS) Application programs

CS370 Spring 2007 Advantages of DBMS Control of data redundancy Data consistency Sharing of data Improved data integrity Improved security Enforcement of standards Improved maintenance through data independence Increased concurrency Improved backup and recovery services

CS370 Spring 2007 Disadvantages of DBMS Complexity Cost of DBMS Size Additional hardware costs Cost of conversion Performance Higher impact of a failure

CS370 Spring 2007 History of Database Systems First-generation –Hierarchical and Network models (mid 1960s) Second generation – Relational model (1980s) Third generation – Extended Relational model – Object-Oriented model (1990s)

CS370 Spring 2007 Overview of Database Models The database system available today can be grouped into five different types/models:- FILE MANAGEMENT SYSTEM MODEL: –In FMS model, each field or data item is stored sequentially on disk in one large file. For the search of a particular record, whole database from the beginning has to be traversed HIERARCHICAL MODEL: –In HDS model, data is organized in a tree structure that originates from a root. Each class of data is located at a different level along a particular branch that stems from root.

CS370 Spring 2007 Overview of Database Models NETWORK DATABASE MODEL: –Network Database relies on either straight lines or cyclical pointers to map out the relationships between different items. RELATIONAL DATABASE MODEL: –The relational database model uses table to organize the data element. –Each table corresponds to an Entity. Each data field become column in a table and each record become a row in the table. OBJECT-ORIENTED MODEL: –The object-oriented model, represents an application entity as a class. –A class captures both the attributes and behavior of entity.

CS370 Spring 2007 Evolution of DB Models