Marjan Sirjani

Modeling component connectors in Reo by constraint automata

In this paper we introduce constraint automata and propose them as an operational model for Reo, an exogenous coordination language for compositional construction of component connectors based on a calculus of channels. By providing composition operators for constraint automata and defining notions of equivalence and refinement relations for them, this paper covers the foundations for building tools to address concerns such as the automated construction of the automaton for a given component connector, equivalence checking or containment checking of the behavior of two given connectors, and verification of coordination mechanisms.

Schedulability of asynchronous real-time concurrent objects

Abstract We present a modular method for schedulability analysis of real time distributed systems. We extend the actor model, as the asynchronous model for concurrent objects, with real time using timed automata, and show how actors can be analyzed individually to make sure that no task misses its deadline. We introduce drivers to specify how an actor can be safely used. Using these drivers we can verify schedulability, for a given scheduler, by doing a reachability check with the U ppaal model checker. Our method makes it possible to put a finite bound on the process queue and still obtain schedulability results that hold for any queue length.

Modelling and simulation of asynchronous real-time systems using Timed Rebeca

Abstract In this paper we propose Timed Rebeca as an extension of the Rebeca language that can be used to model distributed and asynchronous systems with timing constraints. Timed Rebeca restricts the modeller to a pure asynchronous actor-based paradigm, where the structure of the model represents the service oriented architecture, while the computational model matches the network infrastructure. The modeller can specify both computational and network delay, and assign deadlines for serving a request. We provide the formal semantics of the language using Structural Operational Semantics, and show its expressiveness by means of examples. We developed a tool for automated translation from Timed Rebeca to the Erlang language, which provides a first implementation of Timed Rebeca. We can use the tool to set the parameters of Timed Rebeca models, which represent the environment and component variables, and use McErlang to run multiple simulations for different settings. The results of the simulations can then be employed to select the most appropriate values for the parameters in the model. Simulation is shown to be an effective analysis support, specially where model checking faces almost immediate state explosion in an asynchronous setting.

Modeling Component Connectors in Reo by Constraint Automata: (Extended Abstract)

Reo is an exogenous coordination language for compositional construction of component connectors based on a calculus of channels. Building automated tools to address such concerns as equivalence or containment of the behavior of two given connectors, verification of the behavior of a connector, etc. requires an operational semantic model suitable for model checking. In this paper we introduce constraint automata and propose them as a semantic model for Reo.

A front-end tool for automated abstraction and modular verification of actor-based models

Actor-based modeling is known to be an appropriate approach for representing concurrent and distributed systems. Rebeca is an actor-based language with a formal foundation, based on an operational interpretation of the actor model. We develop a front-end tool for translating a subset of Rebeca to SMV in order to model check Rebeca models. Automated modular verification and abstraction techniques are supported by the tool.

Ten years of analyzing actors: Rebeca experience

In this paper, we provide a survey of the different analysis techniques that are provided for the modeling language Rebeca. Rebeca is designed as an imperative actor-based language with the goal of providing an easy to use language for modeling concurrent and distributed systems, with formal verification support. Throughout the paper the language Rebeca and the supporting model checking tools are explained. Abstraction and compositional verification, as well as state-based reduction techniques including symmetry, partial order reduction, and slicing of Rebeca are discussed. We give an overview of a few extensions of Rebeca. For example, we present the modular schedulability analysis of timed actor-based models and formal techniques to check correctness of self-adaptive systems using Rebeca. A summary of design decisions and a brief general comparison of the analysis methods are provided at the end of the paper while specific sections are accompanied with examples and corresponding related work.

Modere: the model-checking engine of Rebeca

Rebeca is an actor-based language with formal semantics that can be used in modeling concurrent and distributed software and protocols. Automatic verification of these systems in the design stage helps develop error free systems. In this paper, we describe the model checking tool developed for verification of Rebeca models. This tool uses partial order reduction technique for reducing the size of the state space generated for a given model. Using this tool for model checking Rebeca yields much better results than the previous attempts for model checking Rebeca.

Formal analysis of policy-based self-adaptive systems

PobSAM is a flexible actor-based model with formal foundation for model-based development of self-adaptive systems. In PobSAM policies are used to control and adapt the system behavior, and allow us to decouple the adaptation concerns from the application code. In this paper, we use the actor-based language Rebeca to model check PobSAM models. Since policies are used to govern the system behavior, it is required to verify if the governing policies are enforced correctly. To this aim, we present a new generic classification of the policy conflicts and provide temporal patterns expressed in LTL to detect each class of conflicts. Moreover, we propose LTL patterns for checking the correctness of adaptation. An approach based on static analysis of adaptation policies is presented to check the system stability as well.

Modeling and analysis of Reo connectors using alloy

Reo is an exogenous coordination language based on a calculus of channel composition. Different formal models have been developed for this language. In this paper, we present a new approach to modeling and analysis of Reo connectors using Alloy which is a lightweight modeling language based on first-order relational logic. We provide a reusable library of Reo channels in Alloy that can be used to create a model of a Reo connector in Alloy. The model is simple and reflects the original structure of the connector. Furthermore, the model of a connector can be reused as a component for constructing more complex connectors. Using the Alloy Analyzer tool, properties expressed as predicates can be verified by automatically analyzing the execution traces of the Reo connector. We handle the context-sensitive behavior of channels as well as optional constraints on the interactions with environment. Our compositional model can be used as an alternative to other existing approaches, and is supported by a well known tool with a rich set of features such as counterexample generation.

Modeling web service interactions using the coordination language Reo

In this paper we propose an approach to derive the formal semantics of WS-BPEL processes compositionally using Reo and constraint automata. We map each WS-BPEL process into a Reo circuit and then construct the corresponding constraint automaton which shows the behavior of the process. The constraint automaton can be used for analyzing the process behavior. Our work covers the core part of the WS-BPEL language including basic and structured activities, correlation sets, variables, and links.