The large diffusion of concurrent and distributed systems has spawned in recent years a variety of new formalisms, equipped with features for supporting an easy specification of such systems. The aim of our paper is to analyze three proposals, namely rewriting logic, action calculi and tile logic, chosen among those formalisms designed for the description of rule-based systems. For each of these logics we first try to understand their foundations, then we briefly sketch some applications. The overall goal of our work is to find out a common layout where these logics can be recast, thus allowing for a comparison and an evaluation of their specific features.

Abstract. We re-examine the standard structural operational semantics of the π-calculus with the view that both process structure and contextual observational power should play roles in describing the behavioural theory. To that end we provide a decomposition of the operational semantics of π which allows for a systematic definition of labelled transitions. These are derived from the calculus ’ underlying reduction rules by following the contexts-as-labels philosophy while being presented using the structural approach. Our novel transition system refines to a composite description of the standard early lts. We generalise our technique to higher-order and asynchronous variants.

We apply to logic programming some recently emerging ideas from the field of reduction-based communicating systems, with the aim of giving evidence of the hidden interactions and the coordination mechanisms that rule the operational machinery of such a programming paradigm. The semantic framework we have chosen for presenting our results is tile logic, which has the advantage of allowing a uniform treatment of goals and observations and of applying abstract categorical tools for proving the results. As main contributions, we mention the finitary presentation of abstract unification, and a concurrent and coordinated abstract semantics consistent with the most common semantics of logic programming. Moreover, the compositionality of the tile semantics is guaranteed by standard results, as it reduces to check that the tile systems associated to logic programs enjoy the tile decomposition property. An extension of the approach for handling constraint systems is also discussed.

One major problem for the specification and verification of software architectures and specially with distributed systems, is when system evolution includes dynamic changes and reconfigurations of components and connections. This paper presents a method for specifying reconfigurations or transformations over the topology of the architecture style, being sure that if the transformation can be specified, then its application over the system will be consistent with respect to the expected architecture style configuration. Styles are described by context-free hyperedge graph grammars. In this context, an instance of an architecture style is determined by a graph generated by the grammar. The formalization of the method...

h ground and open terms in a uniform way. To this aim, transition labels become pairs, whose components are called triggers (expressing the interaction of a context with its arguments) and effect (representing the behavior offered to the rest of the system, i.e. a possible context). Tiles can be represented as rectangles where the horizontal dimension is devoted to the assembling of states and the vertical dimension is dedicated to the evolution of components. Thus, triggers and effects form the left and right sides of tiles, respectively. The vertices of tiles are called interfaces, connecting the input and output observations to the initial (before the step) and final (after the step) configurations. Thanks to the abstract notions of configuration and observation, tiles allow us to develop a theoretical framework parametric in such structures (e.g. graphs or hypergraphs or trees or l-terms rather than terms), and able to capture analogies in the structures by means of suitable auxili

Abstract. This paper is an informal summary of different encoding techniques from process calculi and distributed formalisms to graphic frameworks. The survey includes the use of solo diagrams, term graphs, synchronized hyperedge replacement systems, bigraphs, tile models and interactive systems, all presented at the Dagstuhl Seminar 04241. The common theme of all techniques recalled here is having a graphic presentation that, at the same time, gives both an intuitive visual rendering (of processes, states, etc.) and a rigorous mathematical framework. 1

In recent years, logical frameworks and tile logic have been separately proposed by our research groups, respectively in Udine and in Pisa, as suitable metalanguages with higher-order features for encoding and studying nominal calculi. This paper discusses the main features of the two approaches, tracing di#erences and analogies on the basis of two case studies: late #-calculus and lazy simply typed #-calculus.

this article, we attack the converse problem of explaining semantics as an artifact of syntax, in other words, of extracting the meaning of a program from syntactical considerations on its dynamics, or the way it interacts with the environment. We start the analysis with a very simple slogan, where we use module to mean procedure, in the fashion of (Girard 1987b):

Abstract. Milner’s bigraphs [1] are a general framework for reasoning about distributed and concurrent programming languages. Notably, it has been designed to encompass both the π-calculus [2] and the Ambient calculus [3]. This paper is only concerned with bigraphical syntax: given what we here call a bigraphical signature K, Milner constructs a (pre-) category of bigraphs Bbg(K), whose main features are (1) the presence of relative pushouts (RPOs), which makes them well-behaved w.r.t. bisimulations, and that (2) the so-called structural equations become equalities. Examples of the latter are, e.g., in π and Ambients, renaming of bound variables, associativity and commutativity of parallel composition, or scope extrusion for ν-bound names. Also, bigraphs follow a scoping discipline ensuring that, roughly, bound variables never escape their scope. Here, we reconstruct bigraphs using a standard categorical tool: symmetric monoidal closed (smc) theories. Our theory enforces the same scoping discipline as bigraphs, as a direct property of smc structure. Furthermore, it elucidates the slightly mysterious status of so-called edges in

xtend Definition 13, in order to include also the new concept of algebraicity. In the first version it is was stated as follows. Definition 13 (tile functoriality). Let R = h\Sigma oe ; \Sigma ; N;Ri be an ars. A symmetric equivalence relation =f` A(\Sigma oe ) \Theta A(\Sigma oe ) is functorial for R if, whenever s =f t; s 0 =f t 0 for generic s; s 0 ; t; t 0 elements of A(\Sigma oe ), then s; s 0 =f t; t 0 (whenever defined) and s