1. IT Applications Theory Slideshows
Data Validation
By Mark Kelly
Vceit.com

2. Types
Manual
Electronic

3. 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

4. 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 is clearly not reasonable.

5. What’s reasonable? The main validation checks: Type check Range check
Existence check (or presence check)

6. 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

7. 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.

8. 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

9. 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.

10. 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!

11. 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’)

12. 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

13. 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.

14. 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".

15. 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

16. 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

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

18. Calendar control helps users
User does not have to guess correct date format expected
23/08/09? ?
23 Aug 09?
08/23/09 (US format)?
(Asian format)?

19. 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

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

21. Thanks!
Vceit.com