Specifying software features for composition: a tool-supported approach

Development of several computing and communication technologies is enabling the widespread availability of pervasive systems. In smart home applications, household appliances|such as security alarms, heating systems, doors and windows|are connected to home digital networks. These applications o er features that are typically developed by disparate vendors, and when composed together, these features are expected to work together harmoniously. Engineering these systems poses two main challenges. The rst challenge is: how can developers of individual features specify the features in order to make them composable with other hitherto unknown features? The second challenge is: when composition of features does not produce the desired behaviour, what can be done to resolve this non-intrusively? This article argues that the two issues are intrinsically related, and proposes an approach that addresses the rst challenge in a way that makes the second challenge manageable. In particular, we describe a way of writing feature speci cations in which assumptions about the problem world are made explicit. These feature assumptions can then be evaluated at runtime in order to preserve the desired system behaviour to the extent possible. Our approach is illustrated with examples from smart home applications.