Caribbean Secondary Education Certificate - Information Technology/Methods of Validation and Verification
Data Validation and Verification
Validation is an automatic computer check to ensure that the data entered is sensible and reasonable. It does not check the accuracy of data. For example, suppose you type in a secondary school pupil's year of birth. It is likely to be between 1987 and 1993. A year of birth such as 1966 is impossible. The computer can be programmed only to accept numbers between 1987 and 1993. This is a range check. However, this does not guarantee that the number typed in is right. For example, Darren's year of birth might be 1987. If 1993 is entered, then this is valid, but it is not true.
There are a number of validation types that can help check the data that is being entered. They are used in many different ways:
- Check digit - The last one or two digits on a code are used to check the other digits are correct
- Example - Bar code readers in supermarkets use check digits
- Format check - Checks the data is in the right format
- Example - A National Insurance number is in the form LL 99 99 99 L where L is any letter and 9 is any number
- Length check - Checks the data isn't too short or too long
- Example - A password which needs to be six letters long
- Lookup table - Looks up acceptable values in a table
- Example - There are only seven possible days of the week
- Presence check - Checks that data has been entered into a field
- Example - In most databases a key field cannot be left blank
- Range check - Checks that a value falls within the specified range
- Example - Number of hours worked must be less than 50 and more than 0
- Spell check - Looks up words in a dictionary
- When word processing
Verification is a check to ensure that the data entered exactly matches the original source. There are two main methods of verification:
- Double entry (typing the data in twice and comparing the two copies) - This can take much more time and means higher wage costs.
- Proofreading data - This method involves somebody checking what is on the screen is the same as on the input document. Again, this is time consuming and costly.