08-01-2013, 11:10 AM
Database Systems
Database Systems.ppt (Size: 786.5 KB / Downloads: 298)
Basic Definitions
Database: A collection of related data.
Data: Known facts that can be recorded and have an implicit meaning.
Mini-world: Some part of the real world about which data is stored in a database. For example, student grades and transcripts at a university.
Database Management System (DBMS): A collection of software to facilitate the creation and maintenance of a DB.
Database System: The DBMS software together with the data. Sometimes, applications are also included.
Why the Database Approach?
Application needs constantly changing
Ad hoc questions need rapid answers
Need to reduce long lead times and high cost in new application development
Lots of data shared throughout the organization
Need to improve data consistency and control access to data
Substantial dedicated programming assistance typically not available
Core DB Technology Trend
Relational Database
Distributed Database
Multi-dimensional databases
Object Relational Database
Object-Oriented Database
Multimedia Database
Intelligent Database
Data warehousing, data marts, data mining
Web-based Databases
DBMS
A collection of software
manage different applications for a multi-user database system
enable users to define/create and manipulate data
Basic functions:
multiple user interfaces
controlled redundancy
integrity control
security: authorization & protection
concurrency & recovery control
Features of the E-R Model
Relationships are just as important as entities—they are data that need to be stored in the DB
Most relationships are binary, but they may be ternary (or more!) as well
Questions:
What is the relationship between three binary relationships and a ternary relationship?
Why are there two relationships between projects and employees?
Main Characteristics of the Database Approach
Self-describing nature of a database system: A DBMS catalog stores the description of the database. The description is called meta-data). This allows the DBMS software to work with different databases.
Insulation between programs and data: Called program-data independence. Allows changing data storage structures and operations without having to change the DBMS access programs.
Database Users
Users may be divided into:
those who actually use and control the content (called “Actors on the Scene”)
those who enable the database to be developed and the DBMS software to be designed and implemented (called “Workers Behind the Scene”).