AS Level ICT

Data entry: Validation

Validation

• Validation is a check that is carried out during the process of data entry

• It is also the process by which data is accepted as being sensible and reasonable in the context within which it is being used

• Validation is performed by the computer program that is in use, and consists of a series of checks that are called validation checks

Validation checks

• Validation checks are used to restrict the data that can be entered so that it complies with the data rules that have been laid down

• There are several different type of validation check that can be used, each of which has specific uses

Validation checks

• These validation checks include:– Data type checks– Presence checks– Length checks– File/Table lookups– Cross field checks– Range checks

Validation checks

• These validation checks include:– Format checks– Check digits– Parity checks– Spell checkers– Grammar checkers– Custom dictionaries

Data type checks

• Character type checks make sure that the correct type of data has been entered

Example:• A letter has been entered into a database field that

has been pre-set so that only it will only accept numerical data

• The incorrect data type triggers a warning message and will not allow further data to be entered until the error has been corrected

Data type checks

Presence checks

• Presence checks ensure that data that must be entered is entered

Example:• An online application form for a job requires the

applicant to include their National Insurance number

• If that was not entered the presence check would detect this and notify whoever was entering the data

Length checks

• A length check makes sure that the number of characters entered into field matches that fields requirements

Example:• A National Insurance number will have two letters,

followed by six numbers, followed by one letter (e.g. YY232425A)

Length checks

• If this data is entered into a field specially set up to only accept data that is nine characters long, a length check will immediately identify if more or less than that number of characters has been entered

File/Table lookups

• A lookup table contains a list of valid codes that can be used to enter data

• If a code that is not in the lookup table is entered, it is rejected

• This prevents any incorrect data from being processed

File/Table lookups

Example:• A data management system for a restaurant uses

lookup tables that contain the codes for each course that can be ordered

File/Table lookups

Code

Description

Price

File/Table lookups

• When the unique code is entered, the item description and price are automatically entered

• The system prompts the user to enter a correct code and does do allow incorrect codes to be entered

Cross field checks

• Cross field checks occur when data in one field needs to be checked against data in another field in order for it to make sense

• The simplest forms of cross field checks depend upon the use of check boxes, radio buttons, and/or drop down lists

• In this cases it is simple for the cross field checks to take place

Cross field checks

Example:• The salutation field on a record contains the value

‘Mrs’ but the gender field has been ticked to show the gender is ‘Male’

• The cross field check would identify this anomaly and should flag the record up for checking

Range checks

• Range checks make sure that numerical data falls between pre-determined limits (i.e. within a certain range of numbers)

Example:• Data about a pensioner is being added to a

database• The bottom limit of the age range is 65• If the age is entered as 56, the range check will

display this as an error because the age falls outside the pre-determined limits

Check digits

• When large numbers are entered into a data system there is always a chance of error

• To help to overcome this problem an additional number is often added to the end of the original number

• This number is a check digit, and is calculated from the other numbers in the original number

Check digits

Example:• Check digits are found on barcodes• When the barcode is scanned, the computer

automatically removes the end number and uses the rest of the numbers to calculate what the check digit should be

• If the result is the same, then the number has been entered correctly

Check digits

• The first number (4) is the check digit• Starting from the left, the next number (7) is

multiplied by 11, the second (8) by 10, and so on• The total is then found: 7 x 11 + 8 x 10 + 0 x 9 + 8 x 8

+ 3 x 7 + 2 x 6 + 1 x 5 + 8 x 4 + 1 x 3 + 6 x 2 + 9 x 1 = 315

Example:

Check digits

• 315 is then divided by 11 (there are 11 numbers) and the answer is 28 with a remainder of 7

• The remainder is then deducted from 11 and the result should equal the check digit (11 – 7 = 4)

• As the check digit is 4, the barcode has been entered correctly

Example:

Format checks

• A format check ensures that data conforms to the requisite combination of characters

• It achieves this by the use of a data input mask

Example:• A field in a data management system has been

allocated so that National Insurance numbers can be inputted into it

• The field has a data input mask that will only allow data that follows the correct combination of letters and numbers (e.g. YY232425A [LLNNNNNNL]) to be entered

Parity checks

• When data is transmitted from one computer to another it is important that does not become damaged or ‘corrupted’ during transmission

• Parity checking is a means of doing this• Parity is the sum of the bits within a piece of data• A parity error occurs when one of the bits is

changed

Parity checks

Example:• Data is being transmitted via a data link from one

computer to another• During the transmission of the data there is an

interruption• This may not be noticed by anyone using either

computer, but a parity check will alert them to the fact that data is incomplete or corrupted

Spell checks

• Most computer applications have a spell check function

• This spell check function can usually be ‘enabled’ (switched on) so that it can check the spelling of data as it is entered and automatically identify any mistakes

Spell checks

• The spell check function can – in some applications – be enabled to automatically correct what appear to incorrect spellings, but this option should always be used with caution as it may lead to words that are not recognised but that are spelt correctly being ‘corrected’

Example:• An spell checker set to correct spelling ‘mistakes’

automatically changed a person’s surname from ‘Connew’ to ‘Conned’ – it replaced the correct spelling with another, incorrect word

Grammar checks

• The grammar check function can – in word processing applications – be enabled to identify what appears to be the use of incorrect grammar, and to suggest alternatives

Grammar checks

Example:

Custom dictionaries

• If a spell check function is enabled it should automatically identify any words that it does not recognise

• Spell checkers often fail to recognise proper names (i.e. the names of people or places) or specialist words or jargon

• It is possible to avoid this by setting up customised dictionaries to which words can be added

• Once a word had been add to the customised dictionary, the spellchecker will recognised the new words as being spelt correctly

Custom dictionaries

Example:• A spell check identifies the surname Bellingham as

a spelling mistake• Once that surname is added to the custom

dictionary, it is no longer identified as a spelling mistake as it is now on the list of correctly spelt words that the spell check function checks against

AS Level ICT

Data entry: Validation