The theme of this paper is profunctors, and their centrality and ubiquity in understanding concurrent computation. Profunctors (a.k.a. distributors, or bimodules) are a generalisation of relations to categories. Here they are first presented and motivated via spans of event structures, and the semantics of nondeterministic dataflow. Profunctors are shown to play a key role in relating models for concurrency and to support an interpretation as higher-order processes (where input and output may be processes). Two recent directions of research are described. One is concerned with a language and computational interpretation for profunctors. This addresses the duality between input and output in profunctors. The other is to investigate general spans of event structures (the spans can be viewed as special profunctors) to give causal semantics to higher-order processes. For this it is useful to generalise event structures to allow events which “persist.”

. Models for concurrency can be classified with respect to three relevant parameters: behaviour/system, interleaving/noninterleaving, linear/branching time. When modelling a process, a choice concerning such parameters corresponds to choosing the level of abstraction of the resulting semantics. The classifications are formalized through the medium of category theory. Keywords. Semantics, Concurrency, Models for Concurrency, Categories. Contents 1 Preliminaries 431 2 Deterministic Transition Systems 433 3 Noninterleaving vs. Interleaving Models 436 Synchronization Trees and Labelled Event Structures : : : : : : : : : : : : : : 438 Transition Systems with Independence : : : : : : : : : : : : : : : : : : : : : : 439 4 Behavioural, Linear Time, Noninterleaving Models 441 Semilanguages and Event Structures : : : : : : : : : : : : : : : : : : : : : : : 443 Trace Languages and Event Structures : : : : : : : : : : : : : : : : : : : : : : 446 5 Transition Systems with Independence and Lab...

Models for concurrency can be classified with respect to three relevant parameters: behaviour/system, interleaving/noninterleaving, linear/branching time. When modelling a process, a choice concerning such parameters corresponds to choosing the level of abstraction of the resulting semantics. In this paper, we move a step towards a classification of models for concurrency based on the parameters above. Formally, we choose a representative of any of the eight classes of models obtained by varying the three parameters, and we study the formal relationships between using the language of category theory.

. We present an !-complete algebra of a class of deterministic event structures, which are labelled prime event structures where the labelling function satisfies a certain distinctness condition. The operators of the algebra are summation, sequential composition and join. Each of these gives rise to a monoid; in addition a number of distributivity properties hold. Summation loosely corresponds to choice and join to parallel composition, with however some nonstandard aspects. The space of models is a complete partial order (in fact a complete lattice) in which all operators are continuous; hence minimal fixpoints can be defined inductively. Moreover, the submodel relation can be captured within the algebra by summation (x v y iff x + y = y); therefore the effect of fixpoints can be captured by an infinitary proof rule, yielding a complete proof system for recursively defined deterministic event structures. 1 Introduction It is generally recognised that prime event structures constitut...

Models for concurrency can be classified with respect to the three relevant parameters: behaviour/system, interleaving/noninterleaving, linear /branching time. When modelling a process, a choice concerning such parameters corresponds to choosing the level of abstraction of the resulting semantics. The classifications are formalised through the medium of category theory. Introduction From its beginning, many efforts in the development of the theory of concurrency have been devoted to the study of suitable models for concurrent and distributed processes, and to the formal understanding of their semantics. As a result, in addition to standard models like languages, automata and transition systems [4, 9], models like Petri nets [8], process algebras [6, 2], Hoare traces [3], Mazurkiewicz traces [5], synchronization trees [15] and event structures [7, 16] have been introduced. The idea common to the models above is that they are based on atomic units of change---be they called transition...