AS computing Validation and verification

Introduction It is important to maintain the integrity of any database of information. Any data item must always be the correct data type and always follow the rules for that data. For example, you have a field in your database called ‘NAME’ that was a text data type and up the ten characters long. If you enter a name that was thirty characters long, the data integrity of the database would be lost. Validation and verification techniques are all about ensuing that the data integrity of a database is maintained by ensuring that only the sensible data that you want is stored in it.

Validation Validation is the term used to ensure that only ‘sensible’ data is entered into a database. Sensible data means that it is of the correct data type and it follows any validation rules set up for that field.

Range check You can set up rules to ensure that if someone enters a number it must follow some mathematical rules, for example, be greater then a number, or less than a number. If a value is entered outside of this range, then a helpful error message should be displayed.

Format check Sometimes, especially with ID and membership, the code is made up of a mixture of numbers and letters. For example, a membership ID card is made up of 2 letters, followed by 3 numbers, such as AB123. You can set up rules that look for patterns such as LETTER-LETTER-NUMBER-NUMBER-NUMBER. Wrong data will not get put in the database. It will be rejected and a helpful error message should be displayed.

Length check In text field, you can set up rules that only accept an entry if it is less than a certain number of characters. For example, a field in your database called ‘COLOUR’ is set to be less than 10 characters. If someone entered ‘Blue white and yellow’, it would get rejected because it doesn’t follow the validation rule.

Allowable value check You can set up fields to only accept certain values. For example, you might set up a text field called ‘When do you want to leave?’. So that it can only accept Morning, Afternoon, and Evening.

Check Digit Commonly used on bar code, it is a technique used to see if a number has been entered correctly. A number, called a check digit, is placed at the end of a code. The bar code is read and a maths formula is applied to it. If the result is the same as the check digit, then the code has been read correctly. A method is called ‘modulus 11’ and is used in ISBN numbers. Two special cases in check digit If the remainder is 0, the check digit is 0 If the remainder is 1, the the check digit is X

Check digit example Suppose you have a number 12162?. The question mark at the end is the check digit but what should it be? The check digit will be calculated using ‘modulus 11’ A number, staring at 2 on the right and then working upwards, multiplies each number in the scanned code The multiplied numbers are added, to give is then divided by 11. This equal 3 remainder 9. The remainder is now subtracted from 11 to give the check digit 11 –9 = 2. The check digit is 2.

Presence check Some fields are more important than others and must be filled in. For example, you have a database that stores car adverts. A customer rings up to place an advert and the operator types the advert into the database using a data input form. If the customer does not know the colour of the car, it is not a disaster and so it doesn’t need to be filled in immediately. If the customer ha forgotten his telephone number, how can anyone contact him to buy the car? This field cannot be left blank. If the operator presses ENTER to enter the whole advert without this field being filled in, a helpful error message should be displayed. This method is presence check.