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Research Retrospective
"... The group was exciting in the 1970’s, when we were groping for direction and divided by different orientations. I guess it was in this atmosphere that combined purpose with uncertainty where I found my own voice. The common goal was a transformational program development methodology that would impro ..."
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The group was exciting in the 1970’s, when we were groping for direction and divided by different orientations. I guess it was in this atmosphere that combined purpose with uncertainty where I found my own voice. The common goal was a transformational program development methodology that would improve productivity of designing and maintaining correct software. The emphasis was on algorithmic software. We differed as to how to achieve this goal, and my approach was out on a limb. Based on a few transformations, the most exciting of which was Jay Earley’s iterator inversion combined with high level strength reduction, and also on an overly optimistic faith in the power of science to shed light on this subject, I believed that algorithms and algorithmic software could be designed scientifically from abstract problem specifications by application of a small number of rules, whose selection could be simplified (even automated in some cases) if it could be guided by complexity. Most all others (including the SETL crowd at Courant) disagreed, and accepted the notion that algorithm design was ‘inspired’, and that the most significant steps in a derivation were unexplainable ‘Eureka ’ steps. I knew that my goals were ambitious and with little supporting evidence. In fact the
Applying Symbolic Model Checking to Process Algebras
"... The Simple systems form a class of process algebras whose operational semantics can be specified using finite state labelled transition systems. In this work, we describe how to efficiently derive the ordered Binary Decision Diagrams (BDDs) corresponding to the operational semantics of the terms of ..."
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The Simple systems form a class of process algebras whose operational semantics can be specified using finite state labelled transition systems. In this work, we describe how to efficiently derive the ordered Binary Decision Diagrams (BDDs) corresponding to the operational semantics of the terms of an arbitrary Simple system. Model checking using such BDDs can often speedup the testing of properties such as bisimilarity over direct algorithms. We also introduce a useful extension of Simple providing explicit recursion. For the CCS operators, we show that the corresponding BDD operators we generate automatically are comparable to those coded by hand. 1 Introduction Process algebras are coming into increasing use as specification tools for concurrent systems. Specifications are given as terms; the appropriate use of the algebra's operations lends useful structure to the specifications. As process algebraic specifications resemble programs, they appeal to programmers' intuitions. This st...
A Polyadic Modal µCalculus
, 1994
"... The propositional µcalculus of Kozen extends modal logic with fixed points to achieve a powerful logic for expressing temporal properties of systems modelled by labelled transition systems. We further extend Kozen's logic with polyadic modalities to allow for expressing also quite naturally behavio ..."
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The propositional µcalculus of Kozen extends modal logic with fixed points to achieve a powerful logic for expressing temporal properties of systems modelled by labelled transition systems. We further extend Kozen's logic with polyadic modalities to allow for expressing also quite naturally behavioural relations like bisimulation equivalence and simulation preorders. We show that the problem of model checking is still efficiently decidable, giving rise to efficient worstcase algorithms for verifying the infinity of behavioural relations expressible in this polyadic modal µcalculus. Some of these algorithms compete in efficiency with carefully handcrafted algorithms found in the literature. In spite of this result, the validity problem turns out to be highly undecidable. This is in contrast to the propositional µcalculus where it is decidable in deterministic exponential time. It follows as a corollary, that  also in contrast to the propositional µcalculus  the polyadic modal...
Weak Parametric Failure Equivalences and Their Congruence Formats
"... Weak equivalences are important behavioral equivalences in the course of specifying and analyzing the reactive systems using process algebraic languages. In this paper, we propose a series of weak equivalences named weak parametric failure equivalences, which take two previouslyknown behavioral equ ..."
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Weak equivalences are important behavioral equivalences in the course of specifying and analyzing the reactive systems using process algebraic languages. In this paper, we propose a series of weak equivalences named weak parametric failure equivalences, which take two previouslyknown behavioral equivalences, i.e., the weak failure equivalence and the weak impossible future equivalence, as their special cases. More importantly, based on the idea of the structural operational semantics, a series of rule formats are further presented to congruence format for their corresponding weak parametric failure equivalences, i.e., a specific equivalence is further congruent in any languages satisfying its corresponding congruence format. This series of rule formats reflect the gradual changes in the weak parametric failure equivalences. We conclude that, when the weak parametric failure equivalences become coarser, their corresponding rule formats turn tighter.
2010 13th IEEE International Symposium on Object/Component/ServiceOriented RealTime Distributed Computing Workshops Towards a Modelbased Refinement Process for Contractual State Machines
"... Abstract—We present a rigorous modelbased approach to the stepwise design of contractual state machines, which are a simplified form of statecharts extended with declarative specifications. The approach is based on application of a set of refinement patterns, that can be validated against a formal ..."
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Abstract—We present a rigorous modelbased approach to the stepwise design of contractual state machines, which are a simplified form of statecharts extended with declarative specifications. The approach is based on application of a set of refinement patterns, that can be validated against a formal semantics, and that are implemented using updateinplace model transformations. We describe the integrated tool support we are implementing for this modelbased approach, and illustrate the approach with small examples. I.
Towards a Theory of Glue
"... We propose and study the notions of behaviour type and composition operator making a first step towards the definition of a formal framework for studying behaviour composition in a setting sufficiently general to provide insight into how the componentbased systems should be modelled and compared. W ..."
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We propose and study the notions of behaviour type and composition operator making a first step towards the definition of a formal framework for studying behaviour composition in a setting sufficiently general to provide insight into how the componentbased systems should be modelled and compared. We illustrate the proposed notions on classical examples (Traces, Labelled Transition Systems and Coalgebras). Finally, the definition of memoryless glue operators, takes us one step closer to a formal understanding of the separation of concerns principle stipulating that computational aspects of a system should be localised within its atomic components, whereas coordination layer responsible for managing concurrency should be realised by memoryless glue operators. 1
A Notion of Glue Expressiveness for ComponentBased Systems
"... Abstract. Comparison between different formalisms and models is often by flattening structure and reducing them to behaviorally equivalent models e.g., automaton and Turing machine. This leads to a notion of expressiveness which is not adequate for componentbased systems where separation between be ..."
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Abstract. Comparison between different formalisms and models is often by flattening structure and reducing them to behaviorally equivalent models e.g., automaton and Turing machine. This leads to a notion of expressiveness which is not adequate for componentbased systems where separation between behavior and coordination mechanisms is essential. The paper proposes a notion of glue expressiveness for componentbased frameworks characterizing their ability to coordinate components. Glue is a closed under composition set of operators mapping tuples of behavior into behavior. Glue operators preserve behavioral equivalence. They only restrict the behavior of their arguments by performing memoryless coordination. Behavioral equivalence induces an equivalence on glue operators. We compare expressiveness of two glues G 1 and G 2 by considering whether glue operators of G 1 have equivalent ones in G 2 (strong expressiveness). Weak expressiveness is defined by allowing a finite number of additional behaviors in the arguments of operators of G 2. We propose an SOSstyle definition of glues, where operators are characterized as sets of SOSrules specifying the transition relation of composite components from the transition relations of their constituents. We provide expressiveness results for the glues of BIP and of process algebras such as CCS, CSP and SCCS. We show that for the considered expressiveness criteria, glues of the considered process calculi are less expressive than general SOS glue. Furthermore, glue of BIP has exactly the same strong expressiveness as glue definable by the SOS characterization. 1
DOI: 10.2478/v100060080031x NATURAL QUANTUM OPERATIONAL SEMANTICS WITH PREDICATES
"... A general definition of a quantum predicate and quantum labelled transition systems for finite quantum computation systems is presented. The notion of a quantum predicate as a positive operatorvalued measure is developed. The main results of this paper are a theorem about the existence of generalis ..."
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A general definition of a quantum predicate and quantum labelled transition systems for finite quantum computation systems is presented. The notion of a quantum predicate as a positive operatorvalued measure is developed. The main results of this paper are a theorem about the existence of generalised predicates for quantum programs defined as completely positive maps and a theorem about the existence of a GSOS format for quantum labelled transition systems. The first theorem is a slight generalisation of D’Hondt and Panagaden’s theorem about the quantum weakest precondition in terms of discrete support positive operatorvalued measures.