Databases: Introduction

      UNIT 3 - ⇑ Databases ⇑
      Databases Primary keys →


      Table

      In our database we will store information about 'things', or more technically, entities. To store data about things we use Tables. Each table will store data about a particular thing. Let's look at two examples:

      Database: Crime in a local area
Tables: Crimes, Victims, Criminals, Police Officers

      And looking at another example that you might be familiar with, a social networking site:

      Database: Social Network
Tables: People, Relationships, Messages, Pictures
      Exercise: Picking Tables

      List the tables you might need to store a database on a football League

      Answer :

      Team
Player
Match
Stadium
Referee

      List the tables you might need to record details for an online store

      Answer :

      Staff
Products
Receipts
Customers

      Attribute/Field

      Now we have gotten to grips with recognising the main tables we need to store in each database, we need to recognise what fields of data will be stored in each of these tables. The data items to be stored are called the attributes. Taking the Criminal database as an example:

      Table: Criminal
      Attributes:
      Name: String
      Date of Birth: Date
      Number of scars: Integer
      Home town: String

      Note that for each of the attributes we are listing the attribute name and the field type, when building a database it is very important that we get the correct field type to prevent errors when entering data. Let's take a look at another example from the criminals Database

      Table: Crimes
      NI Number: String
      Description: String
      Type of crime: String
      Severity: Integer
      Dateof Crime: Date
      Victim ID: Integer
      Criminal ID: Integer
      Exercise: Picking attributes

      For a social networking site, what attibutes and data types would you include for the table of people

      Answer :

      Name: string
Date of Birth: Date
Gender: string (character might also work here)
Public profile: boolean
Personal description: String

      For a social networking site, what attibutes and data types would you include for the table of relationships (the table that stores 'friend' 'sister' 'father' etc)

      Answer :

      Person1 ID: integer
Person2 ID: integer
Type of relationship: string
Date created: Date

      Records

      Last modified on 12 June 2013, at 12:02