Product Line Use Cases

Use Cases can be employed in system requirements engineering to capture requirements from an external point of view. In product line modelling, commonalities and variabilities of a family of systems have to be described. In order to support variability modelling for product lines with Use Cases, extensions and modifications of them called Product Line Use Cases (PLUCs) have been defined. We present an approach to derive product line requirements in the form of PLUCs, starting from the analysis of user documentations of existing systems. In order to guarantee the conformance of the derived product with respect to the family we add the capability of expressing constraints over the Product Use Cases (PUCs) that can be derived from a PLUC. The constraints can be expressed as Boolean conditions associated to the variability tags. Using this notation, it is possible to express in the requirements document of the product line not only the possible variant characteristics that can differentiate products of the same family, 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 family, testing is a crucial and expensive part of software development. Yet the derivation of test cases for product families has so far received little attention. We outline a simple methodology for this purpose, which relies on the early requirements specification expressed as PLUCs.