alidation rules validate inputs from users or other systems. The rules can be validated in order to guarantee a successful operation. Validation rules and logic are required when users or systems send a request for process (a simple method call, a Web service, or posting data to a web page) the incoming data have to be validated before going down to underlying services and components to process the requests further.
You can define validation rules on relations, properties value, method call result, … and after validation rules are executed, your application can collect the result from notifications and process them; however, if the validation result did not pass the criteria, the engine would return a false value stored in the notification and the application can collect it to process the request further.
Also, more often than not in a complex system, a validation does not play a role on its own; instead, it needs to be a part of a more complex process. In this scenario, our rules engine provides mechanisms to reuse validation rules as part of an orchestration logic (e.g. Flow, Procedural, Workflow, …).