Computing with actions and communications

Lecture Notes in Computer Science, 2008

In the design process of distributed systems we may have to replace abstract specifications of components by more concrete specifications, thus providing more detailed design information. In the context of process algebra, this well-known approach is often referred to as action refinement. We study the relationships between action refinement and security properties within the Security Process Algebra (SPA). First we formalize the concept of action refinement as a structural inductive transformation. Then we prove several compositional results which can be exploited in the stepwise development of processes. Finally, we consider information flow security properties for SPA processes and define a decidable class of secure processes which is closed under refinement.

Acta informatica, 2001

Process algebras are a frequently used tool for the speci cation and veri cation of distributed reactive systems. In process algebras, actions are used to denote the basic entities of systems. In general, actions are just abstract names with no particular interpretation. The semantics of a system description, given in form of a process algebra term, is not in uenced by t h e c hoice of names. In this paper, we equip a process algebra with a simple semantics for the actions, given in the form of dependencies. The action dependencies are to beinterpreted in the Mazurkiewicz sense: independent actions should be able to commute, or from a di erent perspective should be unordered, whereas dependent actions are always ordered. In this approach, the operators are used to describe the conceptual behavioural structure of the system and the action dependencies determine the minimal necessary orderings and thereby the additionally possible parallelism within this structure.

In this paper, we study reasoning about actions fol- lowing a model checlcing approach in contrast to the usual validity checlcing one. Specifically, we model a dynamic system as a transition graph which represents all the possible system evolutions in terms of state changes caused by actions. Such a transition graph is defined by means of a suitable process algebra asso- ciated with an explicit global store. To reason about system properties we introduce an extension of modal p-calculus. This setting, although directly applica- ble only when complete information on the system is available, has several interesting features for reasoning about actions. On one hand, it inherits from the vast literature on process algebras tools for dealing with complex systems, treating suitably important aspects like parallelism, communications, interruptions, coor- dinations among agents. On the other hand, reasoning by model checking is typically much easier than more general logical services such ...

Science of Computer Programming, 1985

We develop an algebraic theory for the top-down design of communicating systems in which levels of abstraction are represented by algebras, and their stepwise refinements are represented by homomorphisms. Particular attention is paid to the equational specification of these levels of abstraction. A number of examples are included for illustration, most notably a top-down design for a communication protocol.

arXiv (Cornell University), 2010

In this paper we introduced an algebraic semantics for process algebra in form of abstract data types. For that purpose, we developed a particular type of Σ algebra, the seed algebra, which describes exactly the behavior of a process within a labeled transition system. We have shown the possibility of characterizing the bisimulation of two processes with the isomorphism of their corresponding seed algebras. We pointed out that the traditional concept of isomorphism of algebra does not apply here, because there is even no one-one correspondence between the elements of two seed algebras. The lack of this one-one correspondence comes from the non-deterministic choice of transitions of a process. We introduce a technique of hidden operations to mask unwanted details of elements of a seed algebra, which only reflect non-determinism or other implicit control mechanism of process transition. Elements of a seed algebra are considered as indistinguishable if they show the same behavior after these unwanted details are masked. Each class of indistinguishable elements is called a non-hidden closure. We proved that bisimulation of two processes is equivalent to isomorphism of non-hidden closures of two seed algebras representing these two processes. We call this kind of isomorphism a deep isomorphism. We get different models of seed algebra by specifying different axiom systems for the same signature. Each model corresponds to a different kind of bisimulation. By proving the relations between these models we also established relations between 10 different bisimulations, which form a acyclic directed graph.

… of the 8th International Conference on …, 2010

2010

Following the development of formalisms based on data and behavioural aspects of the system, there are number of attempts in which these two formalisms are mixed together to get benefit of both paradigms. 'Circus' being a living specification language with continuous collaboration from both academia and industry, is a combination of Z, CSP and the refinement calculus. To make use of the available and industry-proven tools for a particular programming paradigm, there is a need to develop a formally verified link between the one world and the other. The aim of this work is to develop a formally verified link between a state-rich process algebra i.e. 'Circus' to a state-free process algebra i.e. CSP. To achieve the research goal, the most suitable available tools are to identify. For developing link between targeted formal languages, we will identify the key translations required between the two languages. For ensuring correctness of the translation, we will formalise the key translation / refinement steps. These will form the theoretical core of the work and support the soundness of the link. In the end, we will select and verify a case study from the collection of software / hardware protocols.

The Computer Journal, 1996

A process algebraic foundation is developed, for formal analysis of synchronous hardware designs using the commercially available hardware design language, ELLA. An underlying semantic foundation, based on input/output trace sets, is presented first through the use of state machines. Such a representation enables direct application of standard, fully automated, trace equivalence checking tools. However, to overcome the computational limitations imposed by such analysis methods, the input/output trace semantics is represented through a synchronous process algebra, EPA. Primitive processes in EPA denote the behaviour of primitive hardware components, such as delays or multiplexers, with composition operators corresponding to the different ways in which behaviours may be built. Of particular significance is the parallel composition operator which captures the machinery for building networks from other components/networks. Actions in EPA are structured and signify the state of input and output signals. This structure, however, is abstracted by developing an algebra for the actions. In particular, parallel composition on processes neatly lifts to a special (synchronous) product operation on actions. The EPA representation forms a good basis for semi-automated high-level symbolic manipulation and reasoning tools. Firstly, the original design structure can be maintained, thus easing the problems of user level feedback from tools. Secondly, the application of EPA to ELLA enables a normal form for EPA terms. This provides a route to tractable symbolic verification and simulation, using a state evolution method to establish strong bisimulation properties. The method has been successfully applied to classes of unbounded state space systems.

Foundation of Software …, 1994

More than 15 years ago, Cleaveland and Hennessy proposed an extension of the process algebra CCS in which some actions may take priority over others. The theory was equipped with a behavioral congruence based on strong bisimulation.

Information and Computation, 1993

ory of concurrency; the symbol ; represents We present a simple process algebra which supports a form of refinement of an action by a process and address the question of a n appropriate equivalence relation for it. The main result of the paper is that an adequate equivalence can be defined in a very intuitive manner and moreover can be axiomatized in much the same way as the standard behavioural equivalences.