On Timed Coordination Languages

Although very simple and elegant, Linda-style coordination models lack the notion of time, and are therefore not able to precisely model real-life coordination applications, featuring time-outs and soft real-time constraints. This paper aims at introducing time in these models. To that end, we consider two notions of time, relative time and absolute time, and, for each notion, two types of features. On the one hand, with respect to relative time, we describe two extensions: (i) a delay mechanism to postpone the execution of communication primitives, and (ii) explicit deadlines on the validity of tuples and on the duration of suspension of communication operations. On the other hand, for absolute time, we introduce: (iii) a wait primitive capable of waiting till an absolute point of time, and (iv) time intervals, both on tuples in the data store and on communication operations. The resulting four coordination models are analyzed and compared both from the semantics viewpoint and from the implementation viewpoint. Moreover, a few programming examples suggest their practical interest.