Behavioural, Functional, and Non-functional Contracts for Dynamic Selection of Services

We propose a mechanism for selecting distributed services which encompasses three orthogonal, yet related type of contracts’ compliance. Indeed, we envisage contract compliance as the intersection of behavioural contract compliance with the compliance of functional and non-functional contracts. We model services as communicating-finite state machines (CFSMs) suitably extended to capture data-awareness and application-level quality-of-service (QoS). This extension is instrumental to define our notion of contract compliance in terms of a bisimulation relation for this new class of CFSMs. More precisely, we introduce CFSMs where transitions are decorated with constraints on the payloads while states of CFSMs have decorations that carry QoS contracts. This allows us to capture behavioural contracts (considering the communication pattern as usual in systems of CFSMs) as well as functional and non-functional contracts. We use a case study to assess our approach and we discuss tool support for our framework.