1. 1 AQA ICT AS Level © Nelson Thornes 2008 Good quality data and information Data terms

2. 2 AQA ICT AS Level © Nelson Thornes 2008 Data and information Validation is a technique that can be used to reduce data entry errors. It checks that the data meets certain criteria and gives the user an error message if it does not meet the criteria. Validation cannot stop data entry errors completely. Data could pass the validation check and still be wrong.

3. 3 AQA ICT AS Level © Nelson Thornes 2008 Validation techniques Presence check Range check Format check Length check Lookup check Check digit Commonly used validation techniques:

4. 4 AQA ICT AS Level © Nelson Thornes 2008 Presence check A presence check means you will not be able to continue until you enter data into a field/area. In this example the box must be ticked before the next page can be viewed.

5. 5 AQA ICT AS Level © Nelson Thornes 2008 Range check A range check restricts the values you are allowed to enter. This user has tried to enter the number 137 for an exam which is marked out of 100. An error message pops up until the user enters a number within the valid range.

6. 6 AQA ICT AS Level © Nelson Thornes 2008 A format check makes sure that the data entered follows a particular pattern. Format check If a product code consists of three letters followed by four numbers, a format check would be the best validation technique to use. PAR1956 would be accepted. PART956 would not be accepted because it has four letters and three numbers.

7. 7 AQA ICT AS Level © Nelson Thornes 2008 A check digit is a digit added on the end of a long code of numbers. This check digit is calculated from the others. Check digit If a data entry clerk enters any of the numbers in the wrong order, the system will detect it and display an error message. Bar codes, bank account numbers and ISBN book numbers use check digits. 8329675

8. 8 AQA ICT AS Level © Nelson Thornes 2008 Lookup A lookup is where the number of data options is limited. A dropdown box can be used to show the possibilities. In this example, the possible options are shown as a dropdown menu. This avoids errors in data entry caused by incorrect spelling or choosing a destination that is not offered. It still does not stop the customer choosing the wrong destination.

9. 9 AQA ICT AS Level © Nelson Thornes 2008 Summary Validation helps to make sure that data is reasonable and sensible. It cannot ensure that data is correct. Verification checks data entered against its source. Validating an exam mark between 0 and 100 will stop the user entering a mark of 110, but if a candidate achieved a mark of 73, the validation would not stop an incorrect mark of 37 being entered. Verifying the mark entered against the marks list should spot the error.