Situation-awareness is the ability of applications to adapt to the current situation of their users. For situation-awareness to be truly pervasive it should support the individual needs of every user, everywhere. We present a middleware for pervasive situation-awareness based on the idea of separating the features of a situation from the specification of how it should be recognised. The features of a situation can be seen as an interface that can be easily customised to satisfy individual user needs, while alternative specifications can be used to recognise a situation in different environments. The middleware views situations as collections of roles that individuals and devices play. Its implementation follows an agent-based architecture where collaborating agents acquire and reason over context data. We also show that the middleware can recognise a variety of highly customised situations using alternative specifications with performance that is acceptable for interactive situation-aware applications in realistic deployment sizes.