IT Applications Theory SlideshowsData Validation

By Mark Kellymark@vceit.comVceit.com

Types

• Manual• Electronic

Data Validation• The step taken after data input.• Ensures data are reasonable.• Cannot check for accuracy of data.

• Helps prevents processing of bad data to create bad information.

• GIGO = garbage in, garbage out

Validation

• E.g. a form says a VCE student was born in England.

• Validation can tell it’s reasonable - but it still may be complete rubbish.

• Another form that says the student was born in 45.67 is clearly not reasonable.

What’s reasonable?

• The main validation checks:–Type check–Range check–Existence check (or presence check)

Type check

• A value should be of the right type– Names should be text– Dates should be dd/mm/yyyy format– Number of pets should be numeric– A photo field should contain a JPG image rather

than a spreadsheet– A credit card number field rejects the letter “O”

typed instead of a zero

Range check

• Data should be within a certain range– Kindergarten students’ ages should be between 3

and 6– Number of pets should be >= 0

• Data must exist in a limited list of options– State of residence must be in (Vic, SA, Qld, WA,

ACT, Tas, NT). Sex must be M or F.

Range check

• Data must be unique– e.g. a phone number, customer ID

• Data must be of a minimum, maximum or fixed length – e.g. credit card number has 16 digits

• Data must have a given format– E.g. user ID must have 3 letters and 2 digits– Date must be in dd-mm-yyyy format

Existence check

• Is the data present?• In a pizza delivery list, leaving off the

customer’s name may not be vital, but leaving off the address is.

• Existence check can reject records that lack vital data.

Warning!

• Don’t make validation so strict that valid data are rejected.

• Data can be unexpected but accurate!– kindergarten child could be 8 years old in rare

circumstances– mandating the entry of a phone number would

wrongly reject people with no phone

• Validation should reject absurd data, not slightly odd data!

Bad validation• American websites that insist on a 5 digit zip

code (postcode) – even if you’re not American!• Databases that reject addresses with no Street/

Avenue/Road/Lane (etc) value: some addresses don’t have them.

• Testing for existence in a limited list when the list is not actually limited. (e.g. Title must be one of:Mr, Miss, Mrs, Dr, Sir, Madam’)

Manual & Electronic• Some data needs a human’s common sense to

detect unreasonable entries– Spelling of names– Entry of Adam Sandler in a database of talented

actors– “Jane Smith” registered as a male

• Other checks are better done electronically– Faster, more accurate to get a database to check

for missing ID number values

Some validation techniquesCheck digits • Used for numerical data. An extra digit is

added to a number which is calculated from the digits.

• The computer checks this calculation when data are entered, e.g., The ISBN for a book. The last digit is a check digit calculated using a modulus 11 method.

• Detects mis-typing.

Some validation techniquesSpelling and grammar check • Looks for spelling and grammatical errors. Consistency ChecksChecks fields to ensure data in these fields

corresponds, e.g., If Title = "Mr.", then Gender = "M".

To prevent invalid data entry

Drop-down menus or lists• Force data to be entered from a pre-made

selection– States of Australia– Months of the year

Helping users• Give examples or advice about expected data

formats…

Date (dd/mm/yyyy)Enter your 10-character regocode (case sensitive) __ __ __ __ - __ __ __ __ - __ __

Note how this form clearly indicates which fields are

required and which are optional

Calendar Control• Date cannot be invalid since it must be chosen from a set of valid dates• Can still be inaccurate however!

Calendar control helps users

• User does not have to guess correct date format expected

• 23/08/09?• 23-08-2009?• 23 Aug 09?• 08/23/09 (US format)?• 092308 (Asian format)?

Calendar control helps organisations

• Date data is not ambiguous• Does 02/05/06 entered mean:– 2 May 2006?– 5 Feb 2006?– 6 May 2002?

A bad date could be prevented with good validation

Thanks!

• mark@vceit.com• Vceit.com