Regular expressions are effective ways of implementing such checks.
(See also data type checks below)Checks for missing records.
In modern Relational database values in two tables can be linked through foreign key and primary key.
The computer checks this calculation when data are entered.
For example the last digit of an ISBN for a book is a check digit calculated modulus 10.Compares data in different systems to ensure it is consistent, e.g., The address for the customer with the same id is the same in both systems.
Data validation rules can be defined and designed using any of various methodologies, and be deployed in any of various contexts.
Data validation rules may be defined, designed and deployed, for example: Definition and design contexts: Data that does not conform to these rules will negatively affect business process execution.