2.2 Validation & Verification In this section of the course, you must: Understand the difference between accuracy and validity Explain sources of errors and how they could be overcome Understand the difference between validation and verification Describe appropriate data validation techniques

Accuracy and Validity Accuracy and validity are not the same thing: A valid sentence is one that has the correct grammar – e.g. a noun clause, a verb clause, and another noun clause, such as “the cat sat on the mat” Most people would probably say that an accurate sentence is one that they can verify is true. If you’ve got a cat and it’s on your mat, then the above example is both valid and accurate. If you haven’t even got a cat, then it’s valid but inaccurate! Easy!

Sources of Error How do errors occur in data-entry or transmission?

Verification Verification means checking that the data has been entered correctly; that is that there have been no typing errors, etc., when inputting the data. It is a check for accuracy. Some systems check this by making the user enter the information twice, and then checking that both copies are the same. If they are not, then a mistake must have been made. This is the reason you have to enter the new password twice when you change your network password. Verification is usually a human process.

Validation & Verification Validation means checking that the data makes sense, for example that there are no letters in a field that is supposed to contain only numbers, or that the user hasn’t entered an invalid date, e.g. 30th February. Validation checks validity This is much easier for the computer to perform on its own, as you can give it a set of rules to follow – it would be very difficult for the computer to know whether the data were actually right!

Sources of Error How do errors occur in data-entry or transmission? You could be given the wrong information Data could be omitted Transcription errors could occur The data could be damaged Operator error could lead to double-entry or a record being missed Hardware failure Electrical interference during transmission

Types of Validation There are different types of validation check: Presence – must the data be there? Format (aka picture) – e.g. currency, NI number Range check Lookup – i.e. multiple-choice from either a fixed list or another database table Batch checks – are there the right number of records, or are the totals correct? Check digits and parity