Prentice Hall, 2003

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Database Systems

Week 1

IntroductionBy

Zekrullah Popal

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Data vs. Information

Data: Raw facts; building blocks of information Unprocessed information

Information: Data processed to reveal meaning

Accurate, relevant, and timely information is key to good decision making

Good decision making is key to survival in global environment

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Database definitions:

Def 1: A shared collection of logically related data, designed to meet the information needs of multiple users in an organization. The term database is often erroneously referred to as a synonym for a “database management system (DBMS)”. They are not equivalent and it will be explained in the next section.

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Database definitions (cont…)

Def 2: A collection of data: part numbers, product codes, customer information, etc. It usually refers to data organized and stored on a computer that can be searched and retrieved by a computer program.

Def 3: A data structure that stores metadata, i.e. data about data. More generally we can say an organized collection of information.

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Database definitions (cont…)

Def 4: A collection of information organized and presented to serve a specific purpose. (A telephone book is a common database.) A computerized database is an updated, organized file of machine readable information that is rapidly searched and retrieved by computer.

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Database definitions (cont…)

Def 5: An organized collection of information in computerized format.

Def 6: A collection of related information

about a subject organized in a useful manner that provides a base or foundation for procedures such as retrieving information, drawing conclusions, and making decisions.

Def 7: A Computerized representation of any organizations flow of information and storage of data.

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Types of Databases

Single-user:

Supports only one user at a time

Desktop/Personal Databases

Single-user database running on a personal computer

Multi-user:

Supports multiple users at the same time

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Types of Databases (continued)

Workgroup

Multi-user database that supports a small group of users or a single department

Enterprise

Multi-user database that supports a large group of users or an entire organization

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Location of Databases

Centralized:

Supports data located at a single site

Distributed:

Supports data distributed across several sites

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Disadvantages of File Processing

Program-Data Dependence All programs maintain metadata for each file they use

Duplication of Data Different systems/programs have separate copies of the same data

Limited Data Sharing No centralized control of data

Lengthy Development Times Programmers must design their own file formats

Excessive Program Maintenance 80% of information systems budget

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Problems with Data Dependency

Each application programmer must maintain their own data

Each application program needs to include code for the metadata of each file

Each application program must have its own processing routines for reading, inserting, updating and deleting data

Lack of coordination and central control Non-standard file formats

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Figure 1-2 Three file processing systems at Pine Valley Furniture

Duplicate Data

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Problems with Data Redundancy

Waste of space to have duplicate dataCauses more maintenance headachesThe biggest problem:

When data changes in one file, could cause inconsistencies

Compromises data integrity

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SOLUTION: The DATABASE Approach

Central repository of shared dataData is managed by a controlling

agentStored in a standardized,

convenient form

Requires a Database Management System (DBMS)

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Database Management System

DBMS manages data resources like an operating system manages hardware resources

A software system that is used to create, maintain, and provide controlled access to user databases

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Client/server system architecture

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Elements of the Database Approach

Enterprise Data Model Graphical model showing high-level entities

and relationships for the organization and the relationship among those entities.

Entity: an object or concept that is important to the business.

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One customer may place many orders, but each order is placed by a single customer

One-to-many relationship

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One order has many order lines; each order line is associated with a single order

One-to-many relationship

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One product can be in many order lines, each order line refers to a single product

One-to-many relationship

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Therefore, one order involves many products and one product is involved in many orders

Many-to-many relationship

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Elements of the Database Approach (cont…)

Relational DatabasesDatabase technology involving tables (relations) representing entities and primary/foreign keys representing relationships

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Relationships established in special columns that provide links between tables

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Elements of the Database Approach (cont…) Use of Internet Technology

Networks and telecommunications, distributed databases, client-server

Database Applications Application programs used to perform database

activities (create, read, update, and delete) for database users

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Application program functions: inserting new data, updating existing data, deleting existing data, reading data for display

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Advantages of Databases

Program-Data independence The separation of data description (metadata)

from application programs that use the data. Changing organization’s data with out

changing application programs that process that data.

Minimal data redundancy Previously separate data files are integrated

into a single, logical structure. Some limited redundancy may be desirable to

improve database performance.

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Advantages of Databases (cont…)

Improved data consistency By eliminating data redundancy we greatly

reduce inconsistencies. e.g. customer address stored once

Storage space is not wasted Increased productivity of application

development Cost and time of new database application

is reduced Using functions, using reports and forms

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Advantages of Databases (cont…)

Improved data quality Database designer can specify constraints

Improved data accessibility Select * from product where

product_name= “computer”; Reduced program maintenance

Changes are easily accommodated e.g. adding new data items, changing data formats

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Costs and risks of database approach

New, specialized personals Hire individuals to design and implement, and

administer databases Upgradation of personal if new technology comes to

market Installation and management cost

Install, new release and upgrades, costly software for security

Conversion cost Legacy system: older application in an organization

based on file processing system Legacy to modern

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Costs and risks of database approach

Explicit Backup and recovery Organizational conflicts

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Figure 1-9 Workgroup database with local area network

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Figure 1-10 An enterprise data warehouse

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Components of the Database Environment

CASE Tools – computer-aided software engineering Repository – centralized storehouse of metadata Database Management System (DBMS) – software for managing

the database Database – storehouse of the data Application Programs – software using the data User Interface – text and graphical displays to users Data Administrators – personnel responsible for maintaining the

database System Developers – personnel responsible for designing

databases and software End Users – people who use the applications and databases

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Figure 1-11 Components of the database environment

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Evolution of DB Systems Flat files - 1960s - 1980s Hierarchical – 1970s - 1990s Network – 1970s - 1990s Relational – 1980s - present Object-oriented – 1990s - present Object-relational – 1990s - present Data warehousing – 1980s - present Web-enabled – 1990s - present