Weak Sequential Composition in Process Algebras

n this paper we study a special operator for sequential composition, which is defined relative to a dependency relation over the actions of a given system. The idea is that actions which are not dependent (intuitively because they share no common resources) do not have to wait for one another to proceed, even if they are composed sequentially. Such a notion has been studied before in a linear-time setting, but until recently there has been no systematic investigation in the context of process algebras. We give a structural operational semantics for a process algebraic language containing such a sequential composition operator, which shows some interesting interplay with choice. We give a complete axiomatisation of strong bisimilarity and we show consistency of the operational semantics with an event-based denotational semantics developed recently by the second author. The axiom system allows to derive the communication closed layers law, which in the linear time setting has been shown to be a very useful instrument in correctness preserving transformations. We conclude with a couple of examples

AIDS, Partner Notification and Gender Issues

The interplay between public health, human rights, legal obligations and physicians' ethical concerns was revealed dramatically in Israel in recent cases involving reporting of the HIV positive status of patients. This paper reviews and critically analyses the decision-making process of Israeli Ethics Committees regarding HIV partner notification. One aim of this analysis is to suggest principles that may guide the decision in such cases. It is argued that the resolution concerning disclosure to partners be based on the Principle of Proportionality, taking into account the type of relationship between partner and patient, their cultural background and gender issues. The paper demonstrates the advantages of addressing such issues by professional multidisciplinary Ethics Committees, whose decisions can bring to bear the scope of relevant considerations