Introduction to Databases Software Photo credit: ©2007 JupiterImages Corporation

Learning objectives Understand what a database is and how it works. Understand the purpose of data validation and the procedures involved. Be able to name organizations that use databases and the reasons why they do so. 2 of 16 © Boardworks Ltd 2007

What else can it do? Validation is where the database looks for mistakes in data being entered. The database checks the data against the validation rules, and if the data is not valid, it gives the user an error message. Validation cannot prevent all data entry mistakes, but it can find some.

Validation In our database, one way we could validate the ‘Date of Birth’ field is to make it only accept dates after 1910. We could validate the Number of GCSE Passes field to be less than 20. That wouldn’t stop us entering Jerome’s passes as 1 instead of 7, because 1 and 7 would both be valid. To find that mistake, we would have to verify the data by checking it against the source.

Types of validation Format check – e.g. two letters followed by two numbers – PR15 would be valid but PRX71 would not. Presence check – checking that the field contains any data. Range check –checking that the data is between certain numbers or letters, e.g. A–E. Lookup check – checking that only values from a set list can be entered, e.g. M or F. Size check – checking data falls within a minimum or maximum number of characters.

Error messages If data is entered and it breaks the validation rules, the database can give an error message to explain what is wrong. It is best if error messages are written in plain language to help the user understand what is wrong. For instance, if a field can only contain the data ‘M’ or ‘F’, the message: Entry not valid is not nearly as helpful as: Please enter M or F