Validation and Verification Today will look at: The difference between accuracy and validity Explaining sources of errors and how they could be overcome Understanding the difference between validation and verification Different types of data validation technique

Accuracy and Validity Accuracy and validity are not the same thing, e.g.: 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” – it makes sense and could be possible 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!

Verification Verification means checking that the data is correct; e.g. that there have been no typing or reading errors, etc., when inputting the data. It is a check for accuracy. Some systems check for typing errors by making you type the information twice and checking that both copies are the same. For example, you have to type a new password or address twice when you register on a web-site. If the passwords or addresses are not the same, then a mistake must have been made. Verification is usually a human process, however, because a computer can’t know what is right.

Validation & Verification Validation means checking that the data makes sense, for example that there are no letters in something 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, because 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, but it can tell the difference between letters and numbers, for example. Validation is done by the computer

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 (mistakes in copying data, or typing it in from a printed document) could occur The data could be smudged or damaged You could miss something out (e.g. by turning over two pages), or enter something twice Hardware failure Electrical interference during transmission

Types of Validation There are different types of validation check: Presence – would it be OK to miss out that item? Format – e.g. currency, NI number, postcode Range check – is the value in the right range? Lookup – i.e. multiple-choice from either a fixed list or another database table/spreadsheet range Batch checks – are there the right number of records, or are the totals correct? Check digits and parity (for A level!)

Testing Validation If you created a system including validation, how would you test it? Create a test plan including sample values to try: –Normal data – the types of values you would normally expect –Extreme (or boundary) data – values that are right on the edge of what is acceptable –Erroneous – values that should be rejected

Testing Validation For example, in a system that processed marks from students’ exams there is a field for you to enter the percentage scored in the test. What values should you try in your test plan? –0–0 –100 –Something in the middle – e.g. 50 –101 –-1 Would they be accepted or rejected?

Importance of Accuracy There are many types of systems in use by companies or organisations that contain large amounts of data, e.g. –displaying prices of products on the company web-site –or sending out mail-shots –decision-support systems and management information systems (MIS) that help to run the company… –e.g., the NHS Direct web-site that tries to diagnose illnesses

Importance of Accuracy You've probably used a database or spreadsheet to answer questions as part of your school or ECOS work, and will have come to appreciate that the quality of the answers you can find will only be as good as the quality of the information you have. Any mistakes in the spreadsheet or database will lead to you getting the wrong answers. Imagine that problem multiplied by thousands or millions of times in a large company database and you will see how important it is that the company tries to make sure that their data are accurate. There have been cases in the news of goods being offered at ridiculous prices, and the self-service checkout at Asda never seems to recognise multi-buy offers.

That’s a tempting offer!

Ensuring Accuracy As well as just being careful, there are a number of things a company can do to help to ensure that their data is accurate: –train their staff adequately so that they are less likely to make mistakes, and more likely to spot errors as they occur –employ quality assurance procedures within the company to ensure that staff always follow the correct procedure - this could be something simple like having a checklist to follow when new customers arrive at the company and are added to the database. –use validation and verification at the point where data are entered