Ensuring properties of interaction systems

We propose results ensuring properties of a component-based system from properties of its interaction model and of its components. We consider here deadlock-freedom and local progress of subsystems. This is done in the framework of interaction systems, a model for component based modelling described in [9]. An interaction system is the superposition of two models: a behavior model and an interaction model. The behavior model describes the behavior of individual components. The interaction model describes the way the components may interact by introducing connectors that relate actions from different components. We illustrate our concepts and results with examples. © Springer-Verlag Berlin Heidelberg 2007

Deciding Liveness in Component-Based Systems is NP-hard

Interaction systems are a formal model for component-based systems. Combining components via connectors to form more complex systems may give rise to deadlock situations. In a system that has been shown to be deadlock-free one can ask if a set of components is live. We present here a polynomial time reduction from 3-SAT to the question whether a set of components is live in a deadlock-free system

Deadlock-Detection in Component-Based Systems is NP-hard.

We present a polynomial-time reduction from 3-SAT to DLIS, where DLIS is the set of interaction systems for which a deadlock-state is reachable

Interaction Systems and 1-safe Petri Nets

Interaction systems are a formal model for component-based systems, where components are combined via connectors to form more complex systems. We compare interaction systems (IS) to the wellstudied model of 1-safe Petri nets (1SN) by giving a translation map1: 1SN → IS and a translation map2: IS → 1SN, so that a 1-safe Petri net (an interaction system) and its according interaction system (1-safe Petri net) defined by the respective mapping are isomorphic up to some label relation R. So in some sense both models share the same expressiveness. Also, the encoding map1 is polynomial and can be used to reduce the problems of reachability, deadlock and liveness in 1SN to the problems of reachability, deadlock and liveness in IS, yielding PSPACE-hardness for these questions

Robustness in Interaction Systems

We treat the effect of absence/failure of ports or components on properties of component-based systems. We do so in the framework of interaction systems, a formalism for component-based systems that strictly separates the issues of local behavior and interaction, for which ideas to establish properties of systems where developed. We propose to adapt these ideas to analyze how the properties behave under absence or failure of certain components or merely some ports of components. We demonstrate our approach for the properties local and global deadlock-freedom as well as liveness and local progress

Enhanced Graph Rewriting Systems for Complex Software Domain

International audienceMethodologies for correct by construction reconfigurations can efficiently solve consistency issues in dynamic software architecture. Graph-based models are appropriate for designing such architectures and methods. At the same time, they may be unfit to characterize a system from a non functional perspective. This stems from efficiency and applicability limitations in handling time-varying characteristics and their related dependencies. In order to lift these restrictions, an extension to graph rewriting systems is proposed herein. The suitability of this approach, as well as the restraints of currently available ones, are illustrated, analysed and experimentally evaluated with reference to a concrete example. This investigation demonstrates that the conceived solution can: (i) express any kind of algebraic dependencies between evolving requirements and properties; (ii) significantly ameliorate the efficiency and scalability of system modifications with respect to classic methodologies; (iii) provide an efficient access to attribute values; (iv) be fruitfully exploited in software management systems; (v) guarantee theoretical properties of a grammar, like its termination

Formal Techniques for Component-based Design of Embedded Systems

Embedded systems have become ubiquitous - from avionics and automotive over consumer electronics to medical devices. Failures may entailmaterial damage or compromise safety of human beings. At the same time, shorter product cycles, together with fast growing complexity of the systems to be designed, create a tremendous need for rigorous design techniques. The goal of component-based construction is to build complex systems from simpler components that are well understood and can be (re)used so as to accelerate the design process. This document presents a summary of the formal techniques for component-based design of embedded systems I have (co-)developed

Complexity Results for Reachability in Cooperating Systems and Approximated Reachability by Abstract Over-Approximations

This work deals with theoretic aspects of cooperating systems, i.e., systems that consists of cooperating subsystems. Our main focus lies on the complexity theoretic classification of deciding the reachability problem and on efficiently establishing deadlock-freedom in models of cooperating systems. The formal verification of system properties is an active field of research, first attempts of which go back to the late 60's. The behavior of cooperating systems suffers from the state space explosion problem and can become very large. This is, techniques that are based on an analysis of the reachable state space have a runtime exponential in the number of subsystems. The consequence is that even modern techniques that decide whether or not a system property holds in a system can become unfeasible. We use interaction systems, introduced by Sifakis et al. in 2003, as a formalism to model cooperating systems. The reachability problem and deciding deadlock-freedom in interaction systems was proved to be PSPACE-complete. An approach to deal with this issue is to investigate subclasses of systems in which these problems can be treated efficiently. We show here that the reachability problem remains PSPACE-complete in subclasses of interaction systems with a restricted communication structure. We consider structures that from trees, stars and linear arrangements of subsystems. Our result motivates the research of techniques that treat the reachability problem in these subclasses based on sufficient conditions which exploit characteristics of the structural restrictions. In a second part of this work we investigate an approach to efficiently establish the reachability of states and deadlock-freedom in general interaction systems. We introduce abstract over-approximations -- a concept of compact representations of over-approximations of the reachable behavior of interaction systems. Families of abstract over-approximations are the basis for our approach to establish deadlock-freedom in interaction systems in polynomial time in the size of the underlying interaction system. We introduce an operator called Edge-Match for refining abstract over-approximations. The strength of our approach is illustrated on various parametrized instances of interaction systems. Furthermore, we establish a link between our refinement approach and the field of relational database theory and use this link in order to make a preciseness statement about our refinement approach

Establishing Properties of Interaction Systems

We exhibit sufficient conditions for generic properties of component based systems. The model we use to describe component based systems is the formalism of interaction systems. Because the state space explosion problem is encountered in interaction systems (i.e., an exploration of the state space gets unfeasible for a large number of components), we follow the guideline that these conditions have to be checkable efficiently (i.e., in time polynomial in the number of components). Further, the conditions are designed in such a way that the information gathered is reusable if a condition is not satisfied. Concretely, we consider deadlock-freedom and progress in interaction systems. We state a sufficient condition for deadlock-freedom that is based on an architectural constraint: We define what it means for an interaction system to be tree-like, and we derive a sufficient condition for deadlock-freedom of such systems. Considering progress, we first present a characterization of this property. Then we state a sufficient condition for progress which is based on a directed graph. We combine this condition with the characterization to point out one possibility to proceed if the graph-criterion does not yield progress. Both sufficient conditions can be checked efficiently because they only require the investigation of certain subsystems. Finally, we consider the effect that failure of some parts of the system has on deadlock-freedom and progress. We define robustness of deadlock-freedom respectively progress under failure, and we explain how the sufficient conditions above have to be adapted in order to be also applicable in this new situation