Moritz Martens

An Approach to Modelling and Verification of Component Based Systems

We build on a framework for modelling and investigating component-based systems that strictly separates the description of behavior of components from the way they interact. We discuss various properties of system behavior as liveness, local progress, local and global deadlock, and robustness. We present a criterion that ensures liveness and can be tested in polynomial time.

A Polynomial-Time Checkable Sufficient Condition for Deadlock-Freedom of Component-Based Systems

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. Deciding the existence of deadlocks is NP-hard as it involves global state analysis. We present here a parametrized polynomial-time algorithm that is able to confirm deadlock-freedom for a certain class of interaction systems. The discussion includes characteristic examples and displays the role of the parameter of the algorithm.

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.

Staged Composition Synthesis

A framework for composition synthesis is provided in which metalanguage combinators are supported and the execution of synthesized programs can be staged into composition-time code generation stagei¾?1 and run-time execution stagei¾?2. By extending composition synthesis to encompass both object language L1 and metalanguage L2 combinators, composition synthesis becomes a powerful and flexible framework for the generation of L1-program compositions. A system of modal intersection types is introduced into a combinatory composition language to control the distinction between L1- and L2-combinators at the type level, thereby exposing the language distinction to composition synthesis. We provide a theory of correctness of the framework which ensures that generated compositions of component implementations are well typed and that their execution can be staged such that all metalanguage combinators can be computed away completely at stagei¾?1, leaving only well typed L1-code for execution at stagei¾?2. Our framework has been implemented, and we report on experiments.

Liveness in Interaction Systems

Interaction systems were proposed and implemented by Sifakis et al. as a model for the design and study of component based systems. We investigate here the property of liveness in interaction systems where liveness of an action, a component or a set of components means that the action (component, set of components) will repeatedly participate in every run of the global system. We show that deciding liveness is NP-hard. Then we present a characterization of liveness. Finally, by exploiting local information, we establish a polynomial-time criterion that guarantees liveness. We combine the criterion with the characterization to obtain a test for liveness.

Compositional analysis of deadlock-freedom for tree-like component architectures

We study architectural constraints for component systems in order to be able to guarantee safety-properties. Representing safety-properties, we investigate deadlock-freedom. We present a compositional and hence polynomial time condition for deadlock-freedom for a class of component-systems whose architecture is tree-like. The architectural constraints that are developed can be understood as a design pattern that helps to construct systems satisfying safety-properties on the one hand. On the other hand, they might help to draw attention to potentially critical situations in a design. To model component-systems we use the formalism of interaction systems as proposed by Sifakis et al. The ideas can be transferred to other formal models where subsystems are cooperating via synchronous communication.

Combinatory Logic Synthesizer

We present Combinatory Logic Synthesizer CLS, a type-based tool to automatically compose larger systems from repositories of components. We overview its underlying theory, combinatory logic with intersection types, and exemplify its application to synthesis. We describe features and architecture of the tool and our plans for its ongoing and future development. Finally, we present some use cases in ongoing work, especially in the context of synthesis for Object Oriented Software.

Bounded Combinatory Logic

In combinatory logic one usually assumes a fixed set of basic combinators (axiom schemes), usually K and S. In this setting the set of provable formulas (inhabited types) is PSPACE-complete in simple types and undecidable in intersection types. When arbitrary sets of axiom schemes are considered, the inhabitation problem is undecidable even in simple types (this is known as Linial-Post theorem). k-bounded combinatory logic with intersection types arises from combinatory logic by imposing the bound k on the depth of types (formulae) which may be substituted for type variables in axiom schemes. We consider the inhabitation (provability) problem for k-bounded combinatory logic: Given an arbitrary set of typed combinators and a type tau, is there a combinatory term of type tau in k-bounded combinatory logic? Our main result is that the problem is (k+2)-EXPTIME complete for k-bounded combinatory logic with intersection types, for every fixed k (and hence non-elementary when k is a parameter). We also show that the problem is EXPTIME-complete for simple types, for all k. Theoretically, our results give new insight into the expressive power of intersection types. From an application perspective, our results are useful as a foundation for composition synthesis based on combinatory logic.

Using Architectural Constraints for Deadlock-Freedom of Component Systems with Multiway Cooperation

We present a compositional analysis of deadlock-freedom in component systems with multiway cooperation. We require the systems to satisfy architectural constraints which make sure that the communication structure between the components is given by a tree. Only pairs of components have to be examined for the analysis, therefore the cost is polynomial in the size of the input.

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 were developed.We propose how 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.