Product line use cases: scenario-based specification and testing of requirements

Use Cases can be employed in system requirements engineering to capture requirements from an external point of view. In product line modeling, commonalities and variabilities of a family of systems have to be described. To this purpose, we have defined extensions and modifications of the Use Cases notation, called Product Line Use Cases (PLUCs). In order to guarantee the conformance of the derived product with respect to the product line we add the capability of expressing constraints over the Product Use Cases that can be derived from a PLUC. Using this notation, it is possible to express in the requirements specification of the product line not only the possible variant characteristics that can differentiate products of the same line, but also which combinations of variant characteristics are 'legal' and which are not. Testing is another activity in which PLUCs show their utility. Indeed, for a product belonging to a product line, testing is a crucial and expensive part of software development. Yet the derivation of test cases for product lines has so far received little attention. We outline a simple methodology for this purpose, which relies on the early requirements specification expressed as PLUCs.