Intro. to Database Systems, Lecture notes of Introduction to Database Management Systems

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Chapter 1:

Database System Concepts

and Architecture

Outline

◼ File-based Approach and Database Approach

◼ Three-Schema Architecture and Data

Independence

◼ Database Languages

◼ Data Models, Database Schema, Database

State

◼ Data Management Systems Framework

File-based Approach

◼ Data is stored in one or more separate computer files ◼ Data is then processed by computer programs - applications

File-based Approach

File-based Approach

◼ Problems/Limitations

❑ Data Redundancy

❑ Data Inconsistency

❑ More details: see [2]

Customer Invoicing Purchase Orders Customer Orders Order File Customer File Customer File Stock File Stock File Order File Supplier File Stock File Applications Files Stock Control Stock File Order File

Applications

Files

Purchase

Orders

Stock

Control

Customer

Orders

Customer

File

Stock

File

Order

File

Customer

Invoicing

Supplier

File

Shared file approach

File-based Approach

◼ Shared File Approach

❑ Other problems:

◼ Rigid data structure: If applications have to share files, the file structure that suits one application might not suit another. ◼ Physical data dependency: If the structure of the data file needs to be changed in some way, this alteration will need to be reflected in all application programs that use that data file. ◼ No support of concurrency control: While a data file is being processed by one application, the file will not be available for other applications or for ad hoc queries.

Database Approach

◼ Arose because:

❑ Definition of data was embedded in application

programs, rather than being stored separately and

independently

❑ No control over access and manipulation of data

beyond that imposed by application programs

◼ Result:

❑ The Database and Database Management

System (DBMS).

Database Approach

◼ Data

❑ Known facts that can be recorded and that have

implicit meaning

❑ Information? Knowledge?

❑ More: www.whatis.com

◼ Database: Shared collection of logically related data and a description of this data, designed to meet the information needs of an organization

Database Approach

◼ System catalog (metadata) provides description of data to enable program–data independence. ◼ Logically related data comprises entities, attributes, and relationships of an organization’s information. ◼ D ata B ase M anagement S ystem ( DBMS ): a general- purpose software system that facilitates the processes of defining, constructing, manipulating, and sharing databases among various users and applications ( or a software system that enables users to define, create, maintain, and control access to the database )

Database Approach

◼ Roles in the Database Environment

❑ Database Administrator (DBA): responsible for ◼ authorizing access to DB ◼ coordinating & monitoring its use ◼ acquiring software and hardware resources ◼ security breach, poor response time

❑ Database Designers: responsible for:

◼ identifying the data to be stored in DB ◼ choosing appropriate structures to represent and store this data ❑ Application Programmers ❑ End Users ❑ More details: see [1,2]-chapter 1

◼ DBMS components: Database Approach

Database Approach

◼ History of database systems

❑ First generation: Hierarchical and Network

❑ Second generation: Relational

❑ Third generation: Object-Relational, Object-

Oriented

◼ Brief history of database applications

❑ see [1]-section 1.

Example of Network Model

Schema