On the expressive power of KLAIM-based calculi

We study the expressive power of variants of KLAIM, an experimental language with programming primitives for network-aware programming that combines the process algebra approach with the coordination-oriented one. KLAIM has proved to be suitable for programming a wide range of distributed applications with agents and code mobility, and has been implemented on the top of a runtime system written in Java. In this paper, the expressivity of its constructs is tested by distilling from it a few, more and more foundational, languages and by studying the encoding of each of them into a simpler one. The expressive power of the considered calculi is finally tested by comparing one of them with asynchronous π$\pi$-calculus.     

A note on an expressiveness hierarchy for multi-exit iteration

Multi-exit iteration is a generalization of the standard binary Kleene star operation. The addition of this construct to Basic Process Algebra (BPA) yields a more expressive language than that obtained by augmenting BPA with the standard binary Kleene star. This note offers an expressiveness hierarchy, modulo bisimulation equivalence, for the family of multi-exit iteration operators proposed by Bergstra, Bethke and Ponse.     

On the expressiveness of second-order spider diagrams

Existing diagrammatic notations based on Euler diagrams are mostly limited in expressiveness to monadic first-order logic with an order predicate. The most expressive monadic diagrammatic notation is known as spider diagrams of order. A primary contribution of this paper is to develop and formalise a second-order diagrammatic logic, called second-order spider diagrams, extending spider diagrams of order. A motivation for this lies in the limited expressiveness of first-order logics. They are incapable of defining a variety of common properties, like ‘is even’, which are second-order definable. We show that second-order spider diagrams are at least as expressive as monadic second-order logic. This result is proved by giving a method for constructing a second-order spider diagram for any regular expression. Since monadic second-order logic sentences and regular expressions are equivalent in expressive power, this shows second-order spider diagrams can express any sentence of monadic second-order logic.     

The laws of programming unify process calculi

We survey the well-known algebraic laws of sequential programming, and propose some less familiar laws for concurrent programming. On the basis of these laws, we derive the rules of a number of classical programming and process calculi, for example, those due to Hoare, Milner, and Kahn. The algebraic laws are simpler than each of the calculi derived from it, and they are stronger than all the calculi put together. Conversely, most of the laws are derivable from one or more of the calculi. This suggests that the laws are useful as a presentation of program semantics, and correspond to a widely held common understanding of the meaning of programs. For further evidence, Appendix A describes a realistic and generic model of program behaviour, which has been proved to satisfy the laws.     

On the expressiveness of higher dimensional automata

In this paper I compare the expressive power of several models of concurrency based on their ability to represent causal dependence. To this end, I translate these models, in behaviour preserving ways, into the model of higher dimensional automata (HDA), which is the most expressive model under investigation. In particular, I propose four different translations of Petri nets, corresponding to the four different computational interpretations of nets found in the literature.     

On connections and higher-order logic

This is an expository introduction to an approach to theorem proving in higher-order logic based on establishing appropriate connections between subformulas of an expanded form of the theorem to be proved. Expansion trees and expansion proofs play key roles.This is an extended version of a lecture presented to the 8th International Conference on Automated Deduction in Oxford, England on 27 July 1986. This material is based upon work supported by the National Science Foundation under grants DCR-8402532 and CCR-8702699.     

A process algebra to formalize the Lyee methodology

Over the last years, various methodologies and techniques have been elaborated and proposed to improve one or many aspects related to the software development life cycle. However, despite the great effort in this research field, the production of clearly understood and modifiable systems still an ambitious goal and far from reached. This is due, on one hand, to the complexity and the subtlety of software themselves and, on the other hand, to the limitations of the current methodologies. Recently, a new and very promising methodology, called Lyee, has been proposed. Intended to deal efficiently with a wide range of software problems related to different field, Lyee allows the development of software by simply defining their requirements.

Nevertheless, since both the semantics of Lyee generated software together with the process of automatic generation of software from requirements are described using informal language, difficulties and confusions may arise when trying to understand and study this methodology.

The main purpose of this paper is to formalize, using a process algebra, the process of automatic generation of softwares together with the semantics of Lyee generated softwares. Actually, process algebra naturally supports many concepts of the Lyee methodology and consequently formalize them simply and elegantly. It offers to the Lyee methodology an abstract machine more suitable than the Von-Newman one. In fact, this new abstract machine consider a program as chemical solution when molecules (different vectors of the lyee methodology) interact together to reach a collective goal.     

Processes as formal power series: A coinductive approach to denotational semantics

We characterize must testing equivalence on CSP in terms of the unique homomorphism from the Moore automaton of CSP processes to the final Moore automaton of partial formal power series over a certain semiring. The final automaton is then turned into a CSP-algebra: operators and fixpoints are defined, respectively, via behavioural differential equations and simulation relations. This structure is then shown to be preserved by the final homomorphism. As a result, we obtain a fully abstract compositional model of CSP phrased in purely set-theoretical terms.     

Towards a theory of bisimulation for the higher-order process calculi

In this paper, a labelled transition semantics for higher-order process calculi is studied. The labelled transition semantics is relatively clean and simple, and corresponding bisimulation equivalence can be easily formulated based on it. And the congruence properties of the bisimulation equivalence can be proved easily. To show the correspondence between the proposed semantics and the well-established ones, the bisimulation is characterized as a version of barbed equivalence and a version of context bisimulation.     

On parameterization of higher-order processes

Parameterization provides an effective way to improve on the expressiveness of process-passing. In this paper, we study two kinds of parameterization: name parameterization and process parameterization. Firstly, we show that process parameterization retains the characterization of context bisimulation in terms of the far simpler normal bisimulation, in which universal quantifiers are eliminated. Secondly, we prove that name parameterization is at least as expressive as process parameterization by giving an encoding from the higher-order calculus with process parameterization into the higher-order calculus with name parameterization. These results clarify further the theoretical framework of higher-order processes, and shed light on the relationship between the two kinds of parameterization.     

Sequent calculi and decidability for intuitionistic hybrid logic

In this paper we study the proof theory of the first constructive version of hybrid logic called Intuitionistic Hybrid Logic (IHL) in order to prove its decidability. In this perspective we propose a sequent-style natural deduction system and then the first sequent calculus for this logic. We prove its main properties like soundness, completeness and also the cut-elimination property. Finally we provide, from our calculus, the first decision procedure for IHL and then prove its decidability.     

Proof systems for message-passing process algebras

We give sound and complete proof systems for a variety of bisimulation based equivalences over a message-passing process algebra. The process algebra is a generalisation of pureCCS where the actions consist of receiving and sending messages or data on communication channels; the standard prefixing operatora.p is replaced by the two operatorsc?x.p andc!e.p and in addition messages can be tested by a conditional construct. The various proof systems are parameterised on auxiliary proof systems for deciding on equalities or more general boolean identities over the expression language for data. The completeness of these proof systems are thus relative to the completeness of the auxiliary proof systems.     

On decidability of LTL model checking for process rewrite systems

We establish a decidability boundary of the model checking problem for infinite-state systems defined by Process Rewrite Systems (PRS) or weakly extended Process Rewrite Systems (wPRS), and properties described by basic fragments of action-based Linear Temporal Logic (LTL) with both future and past operators. It is known that the problem for general LTL properties is decidable for Petri nets and for pushdown processes, while it is undecidable for PA processes.We show that the problem is decidable for wPRS if we consider properties defined by LTL formulae with only modalities strict eventually, strict always, and their past counterparts. Moreover, we show that the problem remains undecidable for PA processes even with respect to the LTL fragment with the only modality until or the fragment with modalities next and infinitely often.     

On the expressiveness of interaction

Subbisimilarity is proposed as a general tool to classify the relative expressive power of process calculi. The expressiveness of several variants of CCS is compared in terms of the subbisimilarity relationship. Similar investigation is also carried out for the variants of the pi calculus. The relative expressiveness of the different forms of the choice operation and the different ways of introducing infinite behaviors are systematically studied in both the frameworks of CCS and pi. Some issues concerning the expressiveness of both CCS and pi are clarified. Several open problems are solved along the way. The subbisimilarity approach and the relative expressiveness results are applied to show the independence of the operators of the pi calculus. The definition of the subbisimilarity relationship can be further strengthened with computational requirement, leading to a uniform treatment of computation and interaction.     

Trial-to-trial variability and its influence on higher-order statistics

Firing patterns of neurons are highly variable from trial to trial, even when we record a well-specified neuron exposed to identical stimuli under the same experimental conditions. The trial-to-trial variability of neuronal spike trains may represent some sort of information and provide important indications about neuronal properties. We propose a new method for quantifying the trial-to-trial variability of spike trains, and investigate how the characteristics of noisy neural network models affect the proposed measure. This work was presented in part at the 13th International Symposium on Artificial Life and Robotics, Oita, Japan, January 31–February 2, 2008     

Monolithic and modular termination analyses for higher-order attribute grammars

In this paper we describe a sound, but not complete, analysis to prove the termination of higher-order attribute grammar evaluation caused by the creation of an unbounded number of (finite) trees as local tree-valued attributes, which are then themselves decorated with attributes. The analysis extracts a set of term-rewriting rules from the grammar that model creation of new syntax trees during the evaluation of higher-order attributes. If this term rewriting system terminates, then only a finite number of trees will be created during attribute grammar evaluation. The analysis places an ordering on nonterminals to handle the cases in which higher-order inherited attributes are used to ensure that a finite number of trees are created using such attributes. When paired with the traditional completeness and circularity analyses for attribute grammars and the assumption that each attribute equation defines a terminating computation, this analysis can be used to show that attribute grammar evaluation will terminate normally. This analysis can be applied to a wide range of common attribute grammar idioms and has been used to show that evaluation of our specification of Java 1.4 terminates. We also describe a modular version of the analysis that is performed on independently developed language extension grammars and the host language being extended. If the extensions individually pass the modular analysis then their composition is also guaranteed to terminate.     

On the expressiveness of TPTL and MTL

TPTL and MTL are two classical timed extensions of LTL. In this paper, we prove the 20-year-old conjecture that TPTL is strictly more expressive than MTL. But we show that, surprisingly, the TPTL formula proposed by Alur and Henzinger for witnessing this conjecture it can be expressed in MTL. More generally, we show that TPTL formulae using only modality F can be translated into MTL.