Database Design and Introduction to SQL DBS201 Database Design and Introduction to SQL

Introduction to Database Management

Terminology Application: programs, data, procedures used for some purpose in an organization (eg financial, payroll, equipment maintenance, project management, …) Database: an organized collection of related data for an application DBMS (DataBase Management System): set of programs that manage (create, modify, secure, backup, restore, …) one or more databases (eg Access, DB2, Oracle, SQL Server) Database Design: determining the structure (ie. schema) of the database required for the application

File Based Approach Used in all manual systems and in early computerized systems Duplicates data between applications (eg customer information stored in files for Sales, Customer Service, Billing, …) Increased data maintenance Can create data inconsistencies Very difficult to fulfill requirements that involve data from more than one system

File Based (Non-database) Approach

Database Approach Data for each application is stored in a database and managed by the DBMS Data can only be accessed through the DBMS and not directly through the OS

Database Approach Advantages Easier to combine data from more than 1 application Ability to share data between applications can result in reduced data redundancy (reduced duplication and improved consistency of data) Concurrency: Allows access to data by many different users at the same time Centralized control of data by DBMS and DBA

Advantages of Database (ctd) Improved security and recovery of data Data integrity can be maintained through constraints DBMS development tools reduce programming required Application Flexibility and Data independence : Structure of data can be changed without having to change programs

Disadvantages of Database Approach Complexity of DBMS software requires developers to have specialized skills DBMS overhead: software cost, data storage requirements, processing requirements, DBA responsibilities Greater reliance on reliability of 1 software product (as opposed to many different file-based applications) Applications take more time to design More complex to recover data

Sharing of Data between Applications using a DBMS

History of DBMS’s Mainframe DBMS’s have been used since the 1960s Since the mid-1980s, DBMS’s on PCs possess many of the features of their mainframe counterparts Evolution of DBMS models: Hierarchical, Network, Relational, Object-oriented, Object-relational

Hierarchical Database Model Data is seen as a tree structure and can only be retrieved by navigating through hierarchy A parent record can have many children but a child record can have only 1 parent record Navigation is achieved through use of pointers physically stored with each record

Hierarchical Database Model IBM’s IMS was one of first hierarchical DBMS’s Still used by many large legacy OLTP(online transaction processing) applications Good at handling large volumes of data that only need to be accessed using only predefined paths

Network Database Model Next database model; product examples: IDMS, I-D-S Data is seen as a network of records and relationships between these records Data can only be accessed by navigating through defined relationships Pointers physically stored with each record permit navigation Can represent applications that can not be represented using hierarchical model (eg Henry’s Books)

Relational Database Model Developed after network model Based on mathematical set theory that ensures that data can be retrieved in any way required by an application Data is stored in the form of 2 dimensional tables with no physical pointers Data is related through common columns in separate tables Product Examples: Oracle, DB2, SQL Server