Automatic Verification of Communicative Commitments using Reduction

In spite of the fact that modeling and verification of the Multi-Agent Systems (MASs) have been since long under study, there are several related challenges that should still be addressed. In effect, several frameworks have been established for modeling and verifying the MASs with regard to communicative commitments. A bulky volume of research has been conducted for defining semantics of these systems. Though, formal verification of these systems is still unresolved research problem. Within this context, this paper presents the CTLcom that reforms the CTLC, i.e., the temporal logic of the commitments, so as to enable reasoning about the commitments and fulfillment.  Moreover, the paper introduces a fully-automated method for verification of the logic by means of trimming down the problem of a model that checks the CTLcom to a problem of a model that checks the GCTL*, which is a generalized version of the CTL* with action formulae. By so doing, we take advantage of the CWB-NC automata-based model checker as a tool for verification. Lastly, this paper presents a case study drawn from the business field, that is, the NetBill protocol, illustrates its implementation, and discusses the associated experimental results in order to illustrate the efficiency and effectiveness of the suggested technique.   Keywords: Multi-Agent Systems, Model Checking, Communicative commitment's, Reduction

State-of-the-art on evolution and reactivity

This report starts by, in Chapter 1, outlining aspects of querying and updating resources on the Web and on the Semantic Web, including the development of query and update languages to be carried out within the Rewerse project. From this outline, it becomes clear that several existing research areas and topics are of interest for this work in Rewerse. In the remainder of this report we further present state of the art surveys in a selection of such areas and topics. More precisely: in Chapter 2 we give an overview of logics for reasoning about state change and updates; Chapter 3 is devoted to briefly describing existing update languages for the Web, and also for updating logic programs; in Chapter 4 event-condition-action rules, both in the context of active database systems and in the context of semistructured data, are surveyed; in Chapter 5 we give an overview of some relevant rule-based agents frameworks

Model Checking Commitment-Governed Compositions of Web Services

We propose a new approach towards verifying compositions of web services using model checking. In order to perform such a verification, we transform the web service composition into a Multi-Agent System (MAS) model where the process in charge of the composition and the participating services are represented by agents. We model the behavior of the resulting MAS using the extended Interpreted Systems Programming Language (ISPL+), the dedicated language of the MCMAS+ model checker for MAS. We use commitments between agents to regulate and reason about messages between composite web services. The properties against which the compositions are verified are expressed in the Computation Tree Logic of Commitments (CTLC), an extension of the branching logic CTL that supports commitment modalities. We describe BPEL2ISPL+, a tool we developed to perform the automatic transformation from the web service composition described in Business Process Execution Language (BPEL) into a verifiable MAS model described in ISPL+. The BPEL2ISPL+ tool is applied to a concrete BPEL web service composition and its accurate representation in ISPL+ is obtained. The CTLC properties used to verify the compositions regulated by commitments are represented along with the agents abstracting the participating web services. The MCMAS+ model checker is used to verify the model against these properties, providing thus a new approach to model check agent-based web service compositions governed by commitments

FLACOS’08 Workshop proceedings

The 2nd Workshop on Formal Languages and Analysis of Contract-Oriented Software (FLACOS’08) is held in Malta. The aim of the workshop is to bring together researchers and practitioners working on language-based solutions to contract-oriented software development. The workshop is partially funded by the Nordunet3 project “COSoDIS” (Contract-Oriented Software Development for Internet Services) and it attracted 25 participants. The program consists of 4 regular papers and 10 invited participant presentations

Specifying and Verifying Contract-driven Composite Web Services: a Model Checking Approach

As a promising computing paradigm in the new era of cross-enterprise e-applications, web services technology works as plugin mode to provide a value-added to applications using Service-Oriented Computing (SOC) and Service-Oriented Architecture (SOA). Verification is an important issue in this paradigm, which focuses on abstract business contracts and where services’ behaviors are generally classified in terms of compliance with / violation of their contracts. However, proposed approaches fail to describe in details both compliance and violation behaviors, how the system can distinguish between them, and how the system reacts after each violation. In this context, specifying and automatically generating verification properties are challenging key issues. This thesis proposes a novel approach towards verifying the compliance with contracts regulating the composition of web services. In this approach, properties against which the system is verified are generated automatically from the composition’s implementation. First, Business Process Execution Language (BPEL)that specifies actions within business processes with web services is extended to create custom activities, called labels. Those labels are used as means to represent the specifications and mark the points the developer aims to verify. A significant advantage of this labeling is the ability to target specific points in the design to be verified, which makes this verification very focused. Second, new translation rules from the extended BPEL into ISPL, the input language of the MCMAS model checker, are provided so that model checking the behavior of our contract-driven compositions is possible. The verification properties are expressed in the CTLC logic, which provides a powerful representation for modeling composition contracts using commitment-based multiagent interactions. A detailed case study with experimental results are also reported ins the thesis

Model checking GSM-based multi-agent systems

Business artifacts are a growing topic in service oriented computing. Artifact systems include both data and process descriptions at interface level thereby providing more sophisticated and powerful service inter-operation capabilities. The Guard-Stage-Milestone (GSM) language provides a novel framework for specifying artifact systems that features declarative descriptions of the intended behaviour without requiring an explicit specification of the control flow. While much of the research is focused on the design, deployment and maintenance of GSM programs, the verification of this formalism has received less attention. This thesis aims to contribute to the topic. We put forward a holistic methodology for the practical verification of GSM-based multi-agent systems via model checking. The formal verification faces several challenges: the declarative nature of GSM programs; the mechanisms for data hiding and access control; and the infinite state spaces inherent in the underlying data. We address them in stages. First, we develop a symbolic representation of GSM programs, which makes them amenable to model checking. We then extend GSM to multi-agent systems and map it into a variant of artifact-centric multi-agent systems (AC-MAS), a paradigm based on interpreted systems. This allows us to reason about the knowledge the agents have about the artifact system. Lastly, we investigate predicate abstraction as a key technique to overcome the difficulty of verifying infinite state spaces. We present a technique that lifts 3-valued abstraction to epistemic logic and makes GSM programs amenable to model checking against specifications written in a quantified version of temporal-epistemic logic. The theory serves as a basis for developing a symbolic model checker that implements SMT-based, 3-valued abstraction for GSM-based multi-agent systems. The feasibility of the implementation is demonstrated by verifying GSM programs for concrete applications from the service community.Open Acces

Knowledge Representation Concepts for Automated SLA Management

Outsourcing of complex IT infrastructure to IT service providers has increased substantially during the past years. IT service providers must be able to fulfil their service-quality commitments based upon predefined Service Level Agreements (SLAs) with the service customer. They need to manage, execute and maintain thousands of SLAs for different customers and different types of services, which needs new levels of flexibility and automation not available with the current technology. The complexity of contractual logic in SLAs requires new forms of knowledge representation to automatically draw inferences and execute contractual agreements. A logic-based approach provides several advantages including automated rule chaining allowing for compact knowledge representation as well as flexibility to adapt to rapidly changing business requirements. We suggest adequate logical formalisms for representation and enforcement of SLA rules and describe a proof-of-concept implementation. The article describes selected formalisms of the ContractLog KR and their adequacy for automated SLA management and presents results of experiments to demonstrate flexibility and scalability of the approach.Comment: Paschke, A. and Bichler, M.: Knowledge Representation Concepts for Automated SLA Management, Int. Journal of Decision Support Systems (DSS), submitted 19th March 200

State-of-the-art on evolution and reactivity

This report starts by, in Chapter 1, outlining aspects of querying and updating resources on the Web and on the Semantic Web, including the development of query and update languages to be carried out within the Rewerse project. From this outline, it becomes clear that several existing research areas and topics are of interest for this work in Rewerse. In the remainder of this report we further present state of the art surveys in a selection of such areas and topics. More precisely: in Chapter 2 we give an overview of logics for reasoning about state change and updates; Chapter 3 is devoted to briefly describing existing update languages for the Web, and also for updating logic programs; in Chapter 4 event-condition-action rules, both in the context of active database systems and in the context of semistructured data, are surveyed; in Chapter 5 we give an overview of some relevant rule-based agents frameworks