There are a number of issues involved in the design of database files.

• Data types: see the revision notes in section 5.5.5
   
• Selection of fields: when data has been captured, decisions need to be made on which fields to select to store the data.  Sometimes the decision is made not to select a particular field for inclusion in the database file.  This might because the data is incomplete.
  Sometimes the data is made to select fields that are derived from the data that has been captured.  For example, an address may have been captured in a data capture form as a block of text.  This data would be easier to search and sort if the database file used several fields to store the data.  Typically the following fields might be selected:
  • HOUSE NAME/NUMBER
  • ROAD/STREET
  • TOWN/CITY
  • COUNTY
  • POSTCODE
     
• Coding of data: Coding data can have a number of advantages:
  • it can speed up data entry as less typing is involved
  • it can be easier to validate coded data
  • the screen and printed output can take up less space and be easier to format if the length of the code is fixed (i.e. colours can use a 2 letter code such as Gr, Bl, Bk, Yl for green, blue, black and yellow.  Such codes would take up considerably less space when printed out in a table)
     
• Validation rules: see the revision notes in section 5.3.3