Action Refinement in End-Based Choice Settings

The choice operator is essential for the description of action-based reactive systems. If the atomicity of actions is dropped (e.g. by action refinement), one has to decide when the choice is triggered. The standard approach is to trigger the choice when actions start. This thesis examine the alternative approach that the choice is triggered when actions terminate. This end-based choice is motivated and a process algebra, which contains an end-based choice and an action refinement operator, is established. Consistent semantics (operational, denotational, axiomatical) are given. Furthermore, the difference between the start-based and the end-based choice are examined, in particular with respect to equivalence notions. New equivalence are established, since the standard equivalences are not preserved by the end-based action refinement operator

A True Concurrency Semantics for ET-LOTOS

One of the central objectives of the LOTOS restandardisation activity is to define an enhanced LOTOS language which supports real-time specification. The timed extension is based upon a timed LOTOS proposal ET-LOTOS. This paper defines a (branching-time) non-interleaving semantics for ET-LOTOS without data. As a denotational model a suitable timed extension of Langerak's bundle event structures is used. For guarded recursive processes we show the consistency between our non-interleaving semantics and the ET-LOTOS interleaving semantics. Since our semantical model does not have an explicit notion of the passage of time (as opposed to the interleaving semantics) we are able to handle unguarded recursion and Zeno-behaviours in a perspicuous way