Types & Uses of Databases

Transcription

1 Types & Uses of Databases Connolly/Beggs Chapter 1 Ramakrishnan Chapter 1 Overview What is a database? File-Based Systems What are they? The Database Approach What is it? Data Models Database Management Systems People Types of Database 2

2 File-Based Systems A collection of application programs that perform services for the end-users such as the production of reports. Each program defines and manages its own data. Connolly/Beggs 3 File-Based Systems Application focused Based on manual filing systems Each application has its own set of data Data is divided into application areas Advantages Easy to create Independent sets of data Fast for specialised tasks Cheap 4

3 File-Based Systems - Problems Data Isolation Distinct sets of data Difficult to cross reference Data Redundancy Each application stores the same data e.g. customer records Data Dependence Storage of data depends on application Incompatible file formats Limited Query/Search facilities Ad hoc queries difficult Security Size Application dependent Storing 500GB+ requires specialist hardware and software 5 Two Issues with File-Based File-Based Systems do not support Centralised Data Definition Part of application Not stored separately from application Centralised Access Control Part of application Not controlled independently of application 6

4 Overview What is a database? File-Based Systems What are they? The Database Approach What is it? Data Models Database Management Systems People Types of Database 7 Database Approach A shared collection of logically related data, and a description of this data, designed to meet the information needs of an organisation. Connolly/Begg 8

5 Database Approach Centralised store of data Single repository of data Shared corporate resource Independent of individual applications No one application dictates use, format, etc Self-describing Contains a description of itself Data dictionary Program/application independent 9 Database Approach - Data Model Data Model Single definition of data Separate from application Described independently of use Data Modelling Process of describing data Building a model Abstraction Identifying the entities and relationships in the data 10

6 Database Management System A software system that enables users to define, create, maintain and control access to the database Connolly/Begg Called a DBMS 11 Database Management System Software to manage the database Sits between application and data Application DBMS Data Application 12

7 What does the DBMS do? Controls Changing data structure Creating new data types Removing existing data types Manipulating data Inserting, deleting, updating Accessing data Security Integrity 13 Overview What is a database? File-Based Systems What are they? The Database Approach What is it? Data Models Database Management Systems People Types of Database 14

8 Who works with the DBMS? Database Administrators People who manage the DBMS Database Designers People who design and build the database Application Developers People who write software to access the data End-users People who use the software 15 Types of DBMS Main Commercial Systems Relational Others Network Hierarchical Object-oriented Object-relational Semantic Associative Free-text 16

9 Advantages Improved Data redundancy Data consistency Data sharing Data integrity Standards Scalability Concurrency 17 Disadvantages Complexity Models Cost Software Hardware Training Performance Specialised software is normally quicker Failure Single point of failure 18

10 Overview What is a database? File-Based Systems What are they? The Database Approach What is it? Data Models Database Management Systems People Types of Database 19