In computer science, data validation is the process of data cleansing to ensure data quality, that is, that it is 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 is input to the system.
Data validation is intended to provide certain well-defined guarantees for fitness, accuracy, and consistency for any kinds of user input into an application or automated system. Data validation rules can be defined and designed using various methodologies and be deployed in various contexts.
For every process, there is always inputs and outputs. In order to get the most accurate and correct results, the input must be correct, too.
To guarantee the quality in the results, there must be data validation.