Nominal Equational Logic

AbstractThis paper studies the notion of “freshness” that often occurs in the meta-theory of computer science languages involving various kinds of names. Nominal Equational Logic is an extension of ordinary equational logic with assertions about the freshness of names. It is shown to be both sound and complete for the support interpretation of freshness and equality provided by the Gabbay-Pitts nominal sets model of names, binding and α-conversion

Binding in Nominal Equational Logic

AbstractMany formal systems, particularly in computer science, may be expressed through equations modulated by assertions regarding the 'freshness of names'. It is the presence of binding operators that make such structure non-trivial. Clouston and Pitts's Nominal Equational Logic presented a formalism for this style of reasoning in which support for name binding was implicit. This paper extends this logic to offer explicit support for binding and then demonstrates that such an extension does not in fact add expressivity

Actors, actions, and initiative in normative system specification

The logic of norms, called deontic logic, has been used to specify normative constraints for information systems. For example, one can specify in deontic logic the constraints that a book borrowed from a library should be returned within three weeks, and that if it is not returned, the library should send a reminder. Thus, the notion of obligation to perform an action arises naturally in system specification. Intuitively, deontic logic presupposes the concept of anactor who undertakes actions and is responsible for fulfilling obligations. However, the concept of an actor has not been formalized until now in deontic logic. We present a formalization in dynamic logic, which allows us to express the actor who initiates actions or choices. This is then combined with a formalization, presented earlier, of deontic logic in dynamic logic, which allows us to specify obligations, permissions, and prohibitions to perform an action. The addition of actors allows us to expresswho has the responsibility to perform an action. In addition to the application of the concept of an actor in deontic logic, we discuss two other applications of actors. First, we show how to generalize an approach taken up by De Nicola and Hennessy, who eliminate from CCS in favor of internal and external choice. We show that our generalization allows a more accurate specification of system behavior than is possible without it. Second, we show that actors can be used to resolve a long-standing paradox of deontic logic, called the paradox of free-choice permission. Towards the end of the paper, we discuss whether the concept of an actor can be combined with that of an object to formalize the concept of active objects