Service Choreography Research Articles

Model checking web services choreography in process analysis toolkit

Web service (WS) is an emerging software technology, especially acting an important role in cloud computing. The WS choreography description language (WS-CDL) is the standard for modeling the observable behavior of WS composition across multiple participants from a global point of view. However, it lacks of a formal semantics and could easily lead to misunderstanding and different implementations. In this paper, the WS-CDL based specifications are formally extracted in a communicating sequential process supporting a formal approach to checking WS models. In addition, formalisms and model checking are explicitly illustrated through a simple but non-trivial example with the help of model checker process analysis toolkit (PAT).

Modeling and performance evaluation of service choreography based on stochastic Petri net

Web service composition refers to the creation of new services by combining functionalities provided by existing ones. Current web service choreography proposals, such as WSCI, WS-CDL and BPEL, provide notations for describing the message flows in Web service collaborations. The kernel of WSCI consists of simple communication primitives that may be combined using control-flow constructs expressing sequence, branching, parallelism, synchronization, etc. Many efforts have been made on functional formalization and property verification of WSCI-based service compositions. However, performance facet of WSCI - based service composition is yet to be given the importance it deserves. In this paper, we introduce a stochastic-Petri-net-based approach to predict the performance of web service choreographed using WSCI. This approach translates WSCI-based composition into general stochastic Petri net and obtain s analytical estimation of process-completion - time based on the continuous-time Markov chain derived from the Petri net. In the case study, we use Monte-carlo experiments and confidence interval analysis to validate theoretical evaluations.

Guest Editorial: Special Section on Transactional Web Services

THE Internet, along with its related technologies, has created an interconnected world in which information flows easily and tasks are processed collaboratively. To make service-oriented applications more robust, Web services must be examined from a transactional perspective. By transactional, we mean first defining the actions that guide the execution of Web services when failures arise and then the states that permit claiming the success of this execution following the handling of these failures. A variety of transactional models are reported in the database community. Some of these models can be leveraged and enhanced in response to Web services characteristics while others are not suitable for Web services due to the dynamic nature of Web services, the long-running execution scenarios that Web services take part in, and the successful execution of Web services despite other peers’ failure. Today’s service-oriented applications require advanced transactional models that guarantee integrity and continuity of business processes despite the dynamic nature of the features of the environments hosting the execution of these applications. This special section sheds light on the latest advances in the fields of Web services and transactional models in order to better address advanced research on and experience with transactional Web services. Four papers out of 19 submissions were selected for inclusion in this special section. Each submission was subject to a double-review process by at least three peer reviewers. In the first paper, entitled “Event-Based Design and Runtime Verification of Composite Service Transactional Behavior,” Gaaloul et al. propose an event-driven approach to validate the transactional behavior of Web services taking part in compositions. A composition life cycle consists of four phases, namely, design, execution, monitoring, and reengineering. The verification of this behavior throughout this life cycle is done either at design time to validate recovery mechanisms’ consistency or after runtime to detect execution deviations and repair design errors, and, therefore, formally ensure the execution reliability of Web services. In addition, this verification is based on the Event Calculus formalism, which offers a sound definition for this reliability. In the second paper, entitled “FACTS: A Framework for Fault-Tolerant Composition of Transactional Web Services,” Liu et al. note that delivering reliable compositions over unreliable Web services is challenging. To address this challenge, Liu et al. identify a set of high-level exception handling strategies and a new taxonomy of transactional Web services to devise a fault-tolerant mechanism that combines exception handling and transaction techniques. In addition, Liu et al. devise two modules, known as specification and verification, to assist service designers in constructing fault handling logic conveniently and correctly. This logic is automatically injected into WS-BPEL. In the third paper, entitled “Rule-Based Coordination of Distributed Web Service Transactions,” von Riegen et al. study the distributed transactional activity control problem in the context of service choreographies. In such a context, many participants are allowed to work together to achieve a global, common goal, and the initiator of a process is not always the one who is able to commit or cancel a transaction. Von Riegen et al. introduce a framework that allows autonomous coordination of dynamic processes. This framework extends WSBusinessActivity to strengthen the role of the coordinator. Predicate rules are developed to let participants cancel or complete a process and help the coordinators decide on the completion processes and the confirmation or cancellation of the participants’ works. In the fourth paper, entitled “TQoS: Transactional and QoS-Aware Selection Algorithm for Automatic Web Service Composition,” El Haddad et al. focus on the issues of selecting and composing Web services. A design-time selection algorithm is proposed in which transactional and QoS requirements are both integrated into the selection process. This algorithm is based on the notion of risk that indicates if execution outcomes can either be compensated for or not. Two risk levels of execution in a transactional system are considered: Risk 0, meaning that if the execution is successful, the obtained outcomes can be compensated for by the user, and Risk 1, meaning that the system does not guarantee successful execution, but if it achieves it, the outcomes cannot be compensated for by the user. We hope this special section inspires researchers to develop new transactional models that would guarantee service-oriented applications integrity and continuity. 30 IEEE TRANSACTIONS ON SERVICES COMPUTING, VOL. 3, NO. 1, JANUARY-MARCH 2010

Declarative specification and verification of service choreographiess

Service-oriented computing, an emerging paradigm for architecting and implementing business collaborations within and across organizational boundaries, is currently of interest to both software vendors and scientists. While the technologies for implementing and interconnecting basic services are reaching a good level of maturity, modeling service interaction from a global viewpoint, that is, representing service choreographies, is still an open challenge. The main problem is that, although declarativeness has been identified as a key feature, several proposed approaches specify choreographies by focusing on procedural aspects, leading to over-constrained and over-specified models. To overcome these limits, we propose to adopt DecSerFlow, a truly declarative language, to model choreographies. Thanks to its declarative nature, DecSerFlow semantics can be given in terms of logic-based languages. In particular, we present how DecSerFlow can be mapped onto Linear Temporal Logic and onto Abductive Logic Programming . We show how the mappings onto both formalisms can be concretely exploited to address the enactment of DecSerFlow models, to enrich its expressiveness and to perform a variety of different verification tasks. We illustrate the advantages of using a declarative language in conjunction with logic-based semantics by applying our approach to a running example.

A barred operational semantics for a subset of WS-CDL with time restrictions

Web Services composition provides a way to obtain value-added services by combining several Web Services. WS-CDL (Web Services Choreography Description Language) is a W3C candidate recommendation for the description of peer-to-peer collaborations for the participants in a Web Services composition. However, the semantics of WS-CDL is provided in a textual way, and hence a complete rigorous semantics is lacking. In this paper we focus our attention on the WS-CDL elements related to concurrency, as well as on the collaborations that have timing restrictions associated. We then provide an operational semantics for a relevant subset of WS-CDL, paying special attention to timed collaborations. This operational semantics is based on barred terms, which allow us to capture the current state of the choreography throughout its execution.

Interacting services: From specification to execution

Interacting services play a key role to realize business process integration among different business partners by means of electronic message exchange. In order to provide seamless integration of these services, the messages exchanged as well as their dependencies must be well-defined. Service choreographies are a means to describe the allowed conversations. This article presents a requirements framework for service choreography languages, along which existing choreography languages are assessed. The requirements framework provides the basis for introducing the language BPEL4Chor, which extends the industry standard WS-BPEL with choreography-specific concepts. A validation is provided and integration with executable service orchestrations is discussed.

Choreographing Web Services

This paper introduces the multiagent protocols (MAP) Web service choreography language and demonstrates how service choreographies can be specified, verified, and enacted with a comparatively simple process language. MAP is a directly executable specification, services do not have to be preconfigured at design-time. Instead, a choreography, specified in MAP, can be sent dynamically to a group of distributed peers to execute at runtime. Furthermore, MAP is based on a formal foundation, this allows model checking of the choreography definition prior to live distribution and enactment. A motivating scenario, taken from the AstroGrid science use-cases, serves as the focal point for the paper and highlights the benefits of choreography, through data flow optimization and lack of centralized server. The MAP formal syntax and model checking environment are discussed in the context of the motivating scenario, along with MagentA, an implementation of MAP which provides a concrete, and open-source framework for the enactment of distributed choreographies. MAP is evaluated by demonstrating the languages conformance to the service interaction patterns, a collection of 13 recurring workflow patterns.

A Petri net approach for the design and analysis of Web Services Choreographies

A Web Service is a self-describing, self-contained modular application that can be published, located, and invoked over a network, e.g. the Internet. Web Services composition provides a way to obtain value-added services by combining several Web Services. The composition of Web Services is, therefore, suitable to support enterprise application integration. WS-CDL (Web Services Choreography Description Language) is a W3C candidate recommendation for the description of peer-to-peer collaborations for the participants in a Web Services composition. In this paper we focus our attention on the development of a methodology for the design and validation of composite Web Services using WS-CDL as the language for describing Web Services interactions and Petri nets as a formalism that allows us to simulate and validate the described systems. We specifically intend, then, to capture timed and prioritized collaborations in composite Web Services, so the model of Petri nets that we use is a prioritized version of Time Petri nets.

From WS‐CDL choreography to BPEL process orchestration

PurposeThe web service choreography description language (WS‐CDL) is a specification for describing multi‐party collaboration based on web services from a global point‐of‐view. WS‐CDL is designed to be used in conjunction with the web services business process execution language (WS‐BPEL or BPEL). As WS‐CDL is a new choreography language, there has been doubt about the feasibility of a transformation to BPEL. This article aims to show how BPEL process definitions of parties involved in a choreography can be derived from the global WS‐CDL model and what the limitations of such a derivation are.Design/methodology/approachThe authors implemented a prototype of the mappings as a proof of concept.FindingsThe automatic transformation leverages the quality of software components interacting in the choreography as advocated in the model driven architecture (MDA) concept. The mapping reveals that some information has to be added manually to the generated BPEL, in particular, choice conditions and private activities.Research limitations/implicationsA comprehensive evaluation of WS‐CDL with respect to the interaction patterns is still missing. As a resolution to this issue, the authors propose the modelling of choreographies by the help of a more abstract language – in the sense of being more independent of underlying technology – like UML 2.0 Activity Diagrams.Practical implicationsThe automation of the mapping offers substantial speed‐up of the engineering process. Additionally, the automatic generation of BPEL stubs minimizes the risk of inconsistent process implementations by the parties.Originality/valueThe core contribution is to show how BPEL process definitions for parties involved in a choreography can be derived from a global WS‐CDL model.

Formal interaction specification in public health surveillance systems using [formula omitted]-calculus

This paper provides formal specification of interactions in typical public health surveillance systems involving healthcare agencies at local, state and federal levels. Although few standards exist for exchange of healthcare information, there is a general lack of formal models of the protocols involved in the interactions between the agencies. The quality of medical care provided is an end result of a well designed choreography of diverse services provided by different healthcare entities. One of the major challenges in this field appears to be explicit formal specification of such interactions. Such formal specification work is the first step leading to both design and verification of important properties of public healthcare systems. π -calculus is a formal modeling technique for precise specification of semantics in interacting concurrent systems where mobility is involved. Two different configurations of public health surveillance systems are modelled using π -calculus in this paper.

The Role of Visual Modeling and Model Transformations in Business-driven Development

This paper explores the emerging paradigm of business-driven development, which presupposes a methodology for developing IT solutions that directly satisfy business requirements and needs. At the core of business-driven development are business processes, which are usually modeled by combining graphical and textual notations. During the business-driven development process, business-process models are taken down to the IT level, where they describe the so-called choreography of services in a Service-Oriented Architecture. The derivation of a service choreography based on a business-process model is simple and straightforward for toy examples only—for realistic applications, many challenges at the methodological and technical level have to be solved. This paper explores these challenges and describes selected solutions that have been developed by the research team of the IBM Zurich Research Laboratory.

A mechanism for grid service composition behavior specification and verification

Current grid service choreography proposals remain at the descriptive level, without providing any kind of reasoning mechanism to check the compatibility and validity of grid service composition. How to formalize and verify the behavior of the grid service composition is therefore imperative. A novel process algebra, Cpi-calculus (Conditional Pi-calculus), is proposed in this paper. By analyzing the interactive behavior of composite grid services, we present a grid service composition signature. Based on the signature, we construct Interactive Behavior Model (IABM) for grid service composition and specify the interactive behavior using the Cpi-calculus. The case study shows that the mechanism for grid service specification and verification could be the algebraic foundation to be used afterwards in automatic and dynamic composition.

웹 서비스 코레오그라피를 이용한 자동 웹 서비스 컴포지션 시스템

웹 서비스와 SOA(Service Oriented Architecture)의 확산으로 웹 서비스 컴포지션의 대한 관심도 점차 커져가고 있다. 최근에는 보다 동적이고 지능적인 SOA 환경의 구축을 위해서 자동 웹 서비스 컴포지션에 대한 연구가 활발하게 진행되고 있다. 하지만, 아직까지 자동 웹 서비스 컴포지션에 관한 완전한 해결책은 제시되지 못하고 있으며, 기존의 연구에서는 여러 가지 문제점을 드러내고 있다. 문법적인 정보 기반의 자동 컴포지션은 잘못된 의미 연결로 인하여 컴포지션의 정확성을 떨어뜨린다. 또한 대부분의 연구에서는 추상적인 컴포지션 결과를 만들어내기 때문에, 실제로 실행하기는 어려움이 있다. 본 논문에서는 이러한 문제점들을 개선하기 위하여 웹 서비스 코레오그라피 기반의 자동 웹 서비스 컴포지션 시스템을 제안하고 있다. 제안하는 시스템에서는 컴포지션의 정확성을 향상시켰고, 보다 구체적인 컴포지션 결과를 만들어낼 수 있다. Web Services composition has gained a considerable attention because of the widespread use of the Web Services and SOA. Recently, various researches on automatic Web Services composition are on going to realize more dynamic and intelligent SOA environments. However, there is no complete solution for automatic Web Services composition now and previous researches have several problems. Automatic composition based on syntactic information has low correctness through incorrect semantic linking. Moreover, many researches make an process as the result of composition which is hard for actual execution. In this paper, improved automatic Web Services composition based on Web Services choreography is proposed. In this system, the correctness is improved and the result of composition is more concrete process.

An Introduction to Service Choreographies (Servicechoreographien – eine Einführung)

Summary Service oriented architecture (SOA) is an architectural style for building software systems based on services. Especially in those scenarios where services implement business processes, complex conversations between the services occur. Service choreographies are a means to capture all interaction obligations and constraints from a global perspective. This article introduces choreographies as an important artifact for SOA, compares them to service orchestrations and surveys existing languages for modeling them.

SOPHIE: Use case and evaluation

Services communicate with each other by exchanging self-contained messages. Depending on the specific requirements of the business model they serve and the application domain for which services were deployed, a number of mismatches (i.e. sequence and cardinality of messages exchanges, structure and format of messages and content semantics), can occur which prevent interoperation among a priori compatible services. This paper presents the evaluation of SOPHIE, a conceptual framework for supporting the conceptualization of ontology-based services choreographies. In doing so a three fold approach is taken that considers formal, epistemological and technical aspects. The formal evaluation tries to prove the consistency, completeness and conciseness of ontological model used. The epistemological evaluation enumerates the improvements and differentiating aspect of SOPHIE with respect to existing related work and reviews a number of application areas where the work was successfully applied. Finally, the technical feasibility evaluation tries to demonstrate the viability of the approach from the point of view of the engineering process required to allow the interaction of heterogeneous Semantic Services.

Vista Dinámica y Estática de la Coordinación de Procesos de Negocios: Una Aproximación basada en Restricciones

This article presents an approach for modelling the choreography of the Web services based on constraints in order to achieve a certain degree of automation in its definition. The definition from both the structural and component dynamics of the Web services choreography. This with the objective of doing its representation in terms of a problem of restriction verification. Results of process performance are compared with other approaches, showing that the model is appropriate to achieve automation in the description of the process choreography Web services.

Assessment of Web Services Specifications to Support Long-Running Conversations

Web service is the leading choice of technology among integration designers, as it promises to provide the required integration capability in standardized and inexpensive manner. In order to guarantee consistent and reliable execution of the integrated systems, web services need to support long-running business conversations among services. Web services support these conversations through specifications such as Web Services Choreography Description Language (WS-CDL), Conversation Policy for XML (cpXML) and Web Services Conversation Language (WSCL). This paper develops a set of requirements to support long-running conversations based on Language-Action literatures. These requirements are utilized to assess the above specifications for their ability to support long-running conversations. Assessment reveals that cpXML specification provides better support than WS-CDL and WSCL.

WS-CDL+ for web service collaboration

Web services are becoming the prominent paradigm for distributing, computing, and electronic business, while there is an increasing surge to provide online Business-to-Business collaborations. The Web Services Choreography Description Language (WS-CDL) is a Web service specification developed by W3C, in order to provide peer-to-peer collaborations for participants from different parties. Despite the great research interests it has received during recent years, no practical or even prototype execution engine has been built for WS-CDL, which is, however, essential to test and evaluate the properties of WS-CDL when doing research on it, and also a crucial component to put WS-CDL into the application field. This paper implements an execution engine for WS-CDL, which has never been built before, and enhance its functionalities and usability by introducing six extended features into the execution engine, namely WS-CDL+. Several experiments are then done to test the functionalities and performance of the execution engine, making sure that it works properly according to the WS-CDL+ specification and its performance is acceptable. Finally, the whole paper is concluded, as well as the discussion of the application perspectives of WS-CDL/WS-CDL+.

A Formal Framework for Web Services Coordination

Recently the term Web Services Choreography has been introduced to address some issues related to Web Services Composition and Coordination. Several proposals for describing Choreography for Business Processes have been presented in the last years and many of these languages (e.g. BPEL4WS) make use of concepts as long-running transactions and compensations for coping with error handling. However, the complexity of BPEL4WS makes it difficult to formally define this framework, thus limiting the formal reasoning about the designed applications. In this paper, we formally address Web Services Coordination with particular attention to Web transactions. We enhance our past work - the Event Calculus - introducing two main novelties: i) a multicast event notification mechanism, and ii) event scope names binding. The former enables an easier specification of complex coordination scenarios — such as E-commerce applications require — while the latter allows many new interesting behaviors which can be very useful in business scenarios: the introduction of private event scope names — used to deal with security and privacy — and a dynamic event scopes definition that can be used to manage multiple instances of the same application.

CSP-Based Verification for Web Service Orchestration and Choreography

Service-oriented computing aspires to an unprecedented level of platform-independence and inter-operability of software components for intra- and inter-organizational business processes through standard protocols and languages for workflows and process-oriented applications. The Web Service Business Process Execution Language (WS-BPEL) and the Web Service Choreography Description Language (WS-CDL) are two major languages for modeling and implementing Web services-based business processes. A Web service can be modeled in WS-BPEL by an abstract process describing its external behavior in terms of message exchanges with other participants (Web services). The abstract process can then be refined with more details to become an executable process. On the other hand, WS-CDL serves as a behavioral modeling language for the collaboration between multiple participants (Web services) within the same business process from a global point of view. In this paper, we outline how Communicating Sequential Processes (CSP) can be used as a formal basis for verifying the behavioral consistency among abstract and executable processes together with choreographic descriptions.