IT Applications Theory Slideshows Data Validation By Mark Kelly mark@vceit.com Vceit.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 techniques Check 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 techniques Spelling and grammar check Looks for spelling and grammatical errors. Consistency Checks Checks 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… Enter your 10-character rego code (case sensitive) Date (dd/mm/yyyy) __ __ __ __ - __ __ __ __ - __ __ 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

Because you’ve been good, here’s a picture you can look at

Thanks! mark@vceit.com Vceit.com