We propose a timed and soft extension of Concurrent Constraint Programming. The time extension is based on the hypothesis of bounded asynchrony: the computation takes a bounded period of time and is measured by a discrete global clock. Action prefixing is then considered as the syntactic marker which distinguishes a time instant from the next one. Supported by soft constraints instead of crisp ones, tell and ask agents are now equipped with a preference (or consistency) threshold which is used to determine their success or suspension. In the paper we provide a language to describe the agents behavior, together with its operational and denotational semantics, for which we also prove the compositionality and correctness properties. After presenting a semantics using maximal parallelism of actions, we also describe a version for their interleaving on a single processor (with maximal parallelism for time elapsing). Coordinating agents that need to take decisions both on preference values and time events may benefit from this language. To appear in Theory and Practice of Logic Programming (TPLP).
In @cite_1 , the authors generalize the model in @cite_12 in order to extend it with temporary parametric ask operations. Intuitively, these operations behave as persistent parametric asks during a time-interval, but may disappear afterwards. The presented extension goes in the direction of better modeling with the use of private channels between the agents. However, also the agents in @cite_1 show a deterministic behavior, instead of our not-deterministic choice.
@cite_1 @cite_12
2168318109 2143082793
In this doctoral work we aim at developing a rich timed concurrent constraint (tcc) based language with strong ties to logic. The new calculus called Universal Timed Concurrent Constraint (utcc) increases the expressiveness of tcc languages allowing infinite behaviour and mobility. We introduce a constructor of the form (abs x, c)P (Abstraction in P) that can be viewed as a dual operator of the hidden operator local x in P. i.e. the later can be viewed as an existential quantification on the variable x and the former as an universal quantification of x, executing P[t x] for all t s.t. the current store entails c[t x]. As a compelling application, we applied this calculus to verify security protocols. We develop a model for timed, reactive computation by extending the asynchronous, untimed concurrent constraint programming model in a simple and uniform way. In the spirit of process algebras, we develop some combinators expressible in this model, and reconcile their operational, logical and denotational character. We show how programs may be compiled into finite-state machines with loop-free computations at each state, thus guaranteeing bounded response time. >