Useful Software

We define usefulness of software as conformity to requirements that in turn have to capture user needs, expectations, and create satisfying usage experience.

Users need software to be correct - provide valid output for valid input.

Users expect software to be robust - provide advice on working around invalid input and seeking the valid output.

Obviously, requirements validation is critical in creating useful software, however frequently overlooked or sacrificed - functional prototypes are expensive and time consuming. Executable formal models, such as VDM-SL, provide a very pragmatic way to cover this gap as well as next one - model based testing of the final implementation.