ðHgeocities.com/csit101/Lecture10/Page3.htmlgeocities.com/csit101/Lecture10/Page3.htmlelayedx†ŽÕJÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÈ Ù‹Á#OKtext/html€'9nÁ#ÿÿÿÿb‰.HMon, 01 Nov 1999 18:47:06 GMTBMozilla/4.5 (compatible; HTTrack 3.0x; Windows 98)en, *†ŽÕJÁ# Database

Database

  

 

Definition

A Database is a collection of related data files stored on one or more computers.  Databases prevent redundancies by allowing information sharing.

Example:

  

Advantages

  1. Sharing - Information from one department can be shared with others.
  2. Security - Passwords can be used to prevent access to databases from unauthorized users.
  3. Fewer Files - Less "data redundancy" when same data is used by many departments.
  4. Data Integrity - Can retain accuracy since changes will be consisted throughout all related files.

 

 

Database Management System

  1. Special application software that can be used to create, modify and gain access to a database file.
  2. Database management systems designed especially for microcomputers are Dbase and Access.
  3. There are also database management system designed for minicomputers and mainframes.
  4.  Database management system software is made up of:
    1. Data Dictionary
      1. Contains the structure of the data used in the database
      2. Describes field names, size of the fields, type of data that will be stored in each field.
      3. Key field is also specified.
          
    2. Query Language
      1. An easy-to-use language understandable to most users.
      2. Provides inquiry access to most databases.
      3. The most widely used query language is Structured Query Language (SQL).
        • Made up of commands.
        • Directs the computer to search, display, update, or print records.
        • Examples: 
            
          1. Display all for Sales > Quota.
              

          2. Assuming we have the following enrollment records.
             

            Enrollment Table
            Section Student ID Grade
            303 111 A
            303 222 B
            303 333 C
            303 444 D
            328 111 B
            328 222 A
            3161 333 C
            3161 444 B
             

            To find all sections that the student with ID 111 is enrolled in, we submit the following query to the database:

            select Section from Enrollment where Student_ID = 111

             

 

(page 206)

 

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