Systems Development Lifecycle Validation Routines Learning Objectives Design

Systems Development Lifecycle Validation Routines

Learning Objectives Design validation routines to solve a given problem.

System Development Lifecycle

Design Phase

Data Validation Routines Check input data is sensible and valid before processing.

Range Check Within a pre-determined range. n e. g. The month of a person's DOB should lie between 1 and 12. A telephone bill amount is less than some maximum value for consumer bills.

Presence Check This checks that important data is actually there and has not been missed out. n E. g. Customers may be required to give their telephone numbers or surname.

Existency A code exists. n E. g. Bar code exists in the stock file. Dates actually exist e. g. 31/04/07 or 29/02/07 do not exist but are in the correct format.

Length Check Has the correct number of characters. n E. g. A bank account number may always be 10 digits long. A date must have at least 6 numbers in it. A phone number has 12 numbers.

Character check Check for / Reject particular characters. n E. g. No numbers in text. Hyphen or apostrophe

Type / Format Check A check that data is of the right type. n E. g. Number, Text etc… For currency data - digits point digit

Check digits Used for numerical data. An extra digit is added to a number which is calculated from the number using modular division (dividing by a number and using the remainder as the extra digit). The computer divides by the same number to check this digit. n E. g. The ISBN number on a book is 4534301 453430 / 9 =. . . remainder 1, so 1 is the check digit.

Batch Totals This checks for missing records. Numerical fields may be added together for all records in a batch. The batch total is entered and the computer checks that the total is correct. n E. g. Add the 'Total Cost' field of a number of transactions together.

Hash Totals Some sort of meaningless arithmetic performed on a field. n E. g. Add the Telephone Numbers together for a number of Customers.