In this video, Jeffrey Goldberg explains the importance of having valid and consistent data, and shows how you can achieve that using Mendix.
Validation rules in Mendix are conditions that need to be met before objects can be stored in the database.
Domain model validations are added directly to the attributes of entities. This can control if data entered is unique or matches a specific datatype.
Validations can also be added to microflows and can be used to generate custom error messages for actions and inputs of the end user.
Data consistency is controlled by the relation of association between two objects. This controls what data can be deleted from each object.
If you want to dive deeper into how you can make sure that the data in your app is valid and consistent, go ahead and follow the Rapid Developer learning path: https://bit.ly/2PDnVHn