The Post-validation action sends feedback to help enforce validation.
Simple range and constraint validation may examine user input for consistency with a minimum/maximum range, or consistency with a test for evaluating a sequence of characters, such as one or more tests against regular expressions.
The method is to check that data falls the appropriate parameters defined by the systems analyst.
A judgement as to whether data is valid is made possible by the validation program, but it cannot ensure complete accuracy.
An example of a validation check is the procedure used to verify an ISBN.
Checks to ascertain that only expected characters are present in a field.
Numerical fields may be added together for all records in a batch.
In computer science, data validation is the process of ensuring that data have undergone data cleansing to ensure they have data quality, that is, that they are both correct and useful.
It uses routines, often called "validation rules" "validation constraints" or "check routines", that check for correctness, meaningfulness, and security of data that are input to the system.
For example a numeric field may only allow the digits 0–9, the decimal point and perhaps a minus sign or commas.
A text field such as a personal name might disallow characters such a markup-based security attack.
This is distinct from formal verification, where the operation of a program is determined to be that which was intended, and that meets the purpose.