Databases and Database Management Systems

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Chapter 14

• Databases and Database Management Systems

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Learning Objectives

• Explain what a database is, including common
  database terminology and some of the advantages
  and disadvantages of using databases.
• Discuss some basic concepts and characteristics
  of data, such as hierarchy, entity relationships,
  keys, etc.
• Identify some basic database classifications and
  models and discuss the differences between them.

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Learning Objectives, contd.

• List four types of database models.
• Understand how a relational database is designed,
  created, and used.
• List some ways databases are used on the World
  Wide Web.
• State four key personnel involved with database
  systems.

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Overview

• This chapter covers
• Database management systems
• Database concepts and the evolution of databases
• Database classifications and models
• Web databases
• People who use databases

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What Is a Database?

• A database is a collection of related data stored
  and organized in a manner so it can be retrieved
  as needed.
• Many databases are composed of tables consisting
  of fields and records.
• Sometimes a table is called a file.

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Relational Databases A Simple Example

• A relational database is found most often on PCs.
  
• Data from several different tables can be
  combined quickly using a relational database
  management system.

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File Management Systems vs. Database Management
Systems

• File management system
• Allows the creation of a single database
• Only one file accessed at a time
• Database management system
• Can access data from several different database
  tables at one time
• Has the capability to use multiple tables and
  interrelate them
• Includes helpful tools, such as a query language,
  programming-language facility, etc.

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Interacting with a Database Management System

• Retrieval/update facility
• Allows users to interact with a DBMS
• Usually contains a graphical, menu-driven
  interface that allows users to select choices
  onscreen
• Programming-language facility
• Allows users to create complete computer programs
• Targeted to sophisticated users who desire custom
  menus or screens

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Advantages and Disadvantages of the Database
Approach

• Advantages
• Better information
• Faster response time
• Lower operating costs and storage requirements
• Improved data integrity and better data
  management
• Disadvantages
• Primarily expense
• Increased vulnerability

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Data Hierarchy

• Data in a database is represented by bits and
  bytes that form the characters used in the
  database.
• Characters form field entries.
• Groups of related fields are called records, and
  related records are organized into tables.
• Databases or database files consist of related
  tables.

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Data Definition

• Data definition involves describing the
  properties of the data that goes into each
  database table.
• The finished specifications are referred to as
  the table structure.
• A DDL is a special language component in DBMSs
  for large systems.

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The Data Dictionary

• Data dictionary repository of all data
  definitions in a database.
• Typically kept active to the application.
• Monitors the applications environment to ensure
  that no data is entered or used in a conflicting
  way.
• Many database systems also use the data
  dictionary to provide security for access and/or
  update.

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Data Integrity and Security

• Data integrity refers to the accuracy of data.
• Data validation refers to the process of ensuring
  that data entered into the database matches the
  specifications.
• Data security refers to protecting data against
  destruction and misuse.

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Entity Relationships

• Entity something in a database system that is of
  importance to the organization
• One-to-one relationships
• One-to-many relationships
• Many-to-many relationships

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Data Organization

• Arranging data for efficient retrieval is called
  data organization.
• Key fields
• Sequential organization
• Indexed organization
• Direct organization

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Single-User vs. Multiuser Systems

• Single-user databases are located on a PC and
  designed to be accessed by one user.
• Most business databases are multiuser systems.
• Access to data must be controlled to ensure that
  it is not modified by two users at one time.
• Most systems take care of this by temporarily
  blocking access to data while it is being used.

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Client-Server Systems

• Client-server systems usually consist of a power
  server supplying resources to client PCs.
• The client is called the front end and typically
  runs a relational DBMS.
• The server is called the back end and runs a
  database server program.

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Centralized vs. Distributed Database Systems

• Centralized
• The database is located entirely on a single
  computer.
• Distributed
• Pieces of the database are located on a variety
  of computers, though all users can access the
  entire database just as they would with a
  centralized system.

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The Evolution of Databases

• Flat files
• Hierarchical
• Network
• Relational
• Object-oriented

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The Hierarchical and Network Database Models

• Hierarchical database management system stores
  data in the form of a tree, which sets up a
  one-to-many relationship between data elements.
• Network database management system relationship
  between data elements is usually either
  one-to-many or many-to-many.

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The Relational Database Model

• Designing
• Normalization process
• Structure of table developed
• Creating
• Retrieving information
• Queries and reports
• SQL
• QBE

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The Object-Oriented Database Model

• OODBMS combines multiple types of data.
• Usually accessed using an object-oriented
  programming language or object query language
  (OQL).

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Examples of Web Databases in Use

• Information retrieval
• E-commerce and e-business
• Dynamic Web pages

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How Web Databases Work

• Software that connects two separate applications
  is called middleware.
• Types of middleware include
• CGI
• API
• PHP

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Database Management Systems Personnel

• Administrators
• End users

• Database designers
• Programmers