I'm after some advice regarding data validation and use cases.

We use RUP to gather/document requirements creating use cases for functional requirements and a data catalogue for documenting data items (ie type, format, allowed values etc.). Data items are cross-referenced from use cases. The problem I'm having is where a user enters data as part of the use case flow, should the next step be "The system validates <data item>". My feeling is that this is not required as it only serves to bulk out the use case and create additional alt flows for when the validation fails, however our test community while not insisting on such steps would clearly prefer to see them.

I prefer to rely on the data catalogue to imply this and for the designer to document this in the GUI spec.

Any thoughts appreciated.