Semantics for consistent activation in context-oriented systems

Context: Context-oriented programming languages provide dedicated programming abstractions to define behavioral adaptations and means to combine those adaptations dynamically according to sensed context changes. Some of these languages feature programming abstractions to explicitly define interaction dependencies among contexts. However, the semantics of context activation and the meaning of dependency relations have been described only informally, which in some cases has led to incorrect specifications, faulty implementations and inconsistent system behavior. Objective: With the aim of avoiding faulty implementations and inconsistencies during system execution, this paper proposes both a formal and run-time model of contexts, context activation and context interaction. Method: As a formal and computational basis, we introduce context Petri nets, a model based on Petri nets, which we found to match closely the structure of contexts in context-oriented systems. The operational semantics of Petri nets permits the modeling of run-time context activations, and existing Petri net analyses allow to reason about system properties. As validation, we carried out small and medium-sized case studies. Results: In the explored cases, Context Petri nets served effectively as underlying run-time model to ensure that declared context interaction constraints remain consistent during context manipulation. Moreover, context Petri nets enabled us to analyze certain properties regarding the activation state of particular contexts. Conclusion: Context Petri nets thus proved to be an appropriate formalism to encode and manage the semantics of context activation, both formally and computationally, so as to preserve the consistency of context-oriented systems.