In modern Relational database values in two tables can be linked through foreign key and primary key.
An e-mail address might require at least one @ sign and various other structural details.
Regular expressions are effective ways of implementing such checks.
The rules may be implemented through the automated facilities of a data dictionary, Data validation is intended to provide certain well-defined guarantees for fitness, accuracy, and consistency for any of various kinds of user input into an application or automated system.
Data validation rules can be defined and designed using any of various methodologies, and be deployed in any of various contexts.
It also works well for batch upload, where a file input may be rejected and a set of messages sent back to the input source for why the data is rejected.', '