Categories of processes enriched in final coalgebras

Abstract

Simulations between processes can be understood in terms of coalgebra homomorphisms, with homomorphisms to the final coalgebra exactly identifying bisimilar processes. The elements of the final coalgebra are thus natural representatives of bisimilarity classes, and a denotational semantics of processes can be developed in a final-coalgebraenriched category where arrows are processes, canonically represented. In the present paper, we describe a general framework for building finalcoalgebra- enriched categories. Every such category is constructed from a multivariant functor representing a notion of process, much like Moggi’s categories of computations arising from monads as notions of computation. The “notion of process” functors are intended to capture different flavors of processes as dynamically extended computations. These functors may involve a computational (co)monad, so that a process category in many cases contains an associated computational category as a retract. We further discuss categories of resumptions and of hyperfunctions, which are the main examples of process categories. Very informally, the resumptions can be understood as computations extended in time, whereas hypercomputations are extended in space.