Publikationen zum Fachbereich Exchangeability

Publikationen in Zeitschriften und B�chern

Christian Stahl, Peter Massuthe, and Jan Bretschneider. Deciding Substitutability of Services with Operating Guidelines. Transactions on Petri Nets and Other Models of Concurrency II, Special Issue on Concurrency in Process-Aware Information Systems, 2(5460): 172-191, March 2009.

Abstract: Deciding whether a service S can be substituted by another service S' is an important problem in practice and one of the research challenges in service-oriented computing. In this paper, we define three substitutability notions for services. Accordance specifies that S' cooperates with at least the environments that S cooperates with. S and S' are equivalent if they cooperate with the same environments. To guarantee that S' cooperates with a fixed subset of environments that S cooperates with, the notion of restriction can be used. For each substitutability notion we present a decision algorithm. To this end we apply the concept of an operating guideline of a service as an abstract representation of all environments the service cooperates with.

Christian Stahl and Karsten Wolf. Deciding Service Composition and Substitutability Using Extended Operating Guidelines. Data Knowl. Eng., 68(9): 819-833, 2009.

Abstract: We study the correct interaction between services using the following notion for correctness: there is no deadlock in the interaction of the services, and a given set of activities is not dead, that is, each activity in this set is executed in at least one run. The second condition has not been studied before. An operating guideline of a service P is an operational characterization of all deadlock-free interacting partners of P. In this paper, we present an extension of the concept of an operating guideline to characterize all correctly interacting partners of a service P. This extension can be used for answering at least the following two questions. First, given a service R, does R interact correctly with P? Second, given a service P', can P be substituted by P', that is, is every correctly interacting partner of P a correctly interacting partner of P', too?

Wil M. P. van der Aalst, Niels Lohmann, Peter Massuthe, Christian Stahl, and Karsten Wolf. Multiparty Contracts: Agreeing and Implementing Interorganizational Processes. The Computer Journal, 2008. Note: (Accepted for publication).

Abstract: To implement an interorganizational process between different enterprizes, one needs to agree on the ``rules of engagement''. These can be specified in terms of a contract that describes the overall intended process and the duties of all parties involved. We propose to use such a process-oriented contract which can be seen as the composition of the public views of all participating parties. Based on this contract each party may locally implement its part of the contract such that the implementation (the private view) agrees on the contract. In this paper, we propose a formal notion for such process-oriented contracts and give a criterion for accordance between a private view and its public view. The public view of a party can be substituted by a private view if and only if the private view accords with the public view. Using the notion of accordance the overall implemented process is guaranteed to be deadlock-free and it is always possible to terminate properly. In addition, we present a technique for automatically checking our accordance criterion. A case study illustrates how our proposed approach can be used in practice.

Wolfgang Reisig, Karsten Wolf, Jan Bretschneider, Kathrin Kaschner, Niels Lohmann, Peter Massuthe, and Christian Stahl. Challenges in a Service-Oriented World. ERCIM News, 70: 28-29, July 2007.

Abstract: Interacting services raise a number of new software engineering challenges. To meet these challenges, the behaviour of the involved services must be considered. We present results regarding the behaviour of services in isolation, the interaction of services in choreographies, the exchangeability of a service, and the synthesis of desired partner services.

Konferenzbeitr�ge und Beitr�ge auf Workshops

Jarungjit Parnji, Christian Stahl, and Karsten Wolf. A finite representation of all substitutable services and its applications. In Oliver Kopp and Niels Lohmann, editors, Services and their Composition, 1st Central-European Workshop on, ZEUS 2009, Stuttgart, Germany, March 2--3, 2009, volume 438 of CEUR Workshop Proceedings, pages 8-14, March 2009. CEUR-WS.org.

Abstract: We present a finite representation of all substitutable services P' of a given service P. We show that our approach can be used for at least two applications: (1) given a finite set of services \mathcal{P} = {P1, ..., Pn}, we provide a representation of all services P' that can substitute every Pi \in \mathcal{P}, and (2) given a service P'' that cannot substitute a service P, we find the most similar service P* to P'' that can substitute P.

Wil M. P. van der Aalst, Arjan J. Mooij, Christian Stahl, and Karsten Wolf. Service Interaction: Patterns, Formalization, and Analysis. In Marco Bernardo, Luca Padovani, and Gianluigi Zavattaro, editors, Formal Methods for Web Services (SFM 2009), volume 5569, pages 42--88, April 2009. Springer-Verlag.

Abstract: As systems become more service oriented and processes increasingly cross organizational boundaries, interaction becomes more important. New technologies support the development of such systems. However, the paradigm shift towards service orientation, requires a fundamentally different way of looking at processes. This survey aims to provide some foundational notions related to service interaction. A set of service interaction patterns is given to illustrate the challenges in this domain. Moreover, key results are given for three of these challenges: (1) How to expose a service?, (2) How to replace and refine services?, and (3) How to generate service adapters? These challenges will be addressed in a Petri net setting. However, the results extend to other languages used in this domain.

Wil M. P. van der Aalst, Niels Lohmann, Peter Massuthe, Christian Stahl, and Karsten Wolf. From Public Views to Private Views -- Correctness-by-Design for Services. In Marlon Dumas and Reiko Heckel, editors, Web Services and Formal Methods, Forth International Workshop, WS-FM 2007 Brisbane, Australia, September 28-29, 2007, Proceedings, volume 4937 of Lecture Notes in Computer Science, pages 139-153, 2008. Springer-Verlag.

Abstract: Service orientation is a means for integrating across diverse systems. Each resource, whether an application, system, or trading partner, can be accessed as a service. The resulting architecture, often referred to as SOA, has been an important enabler for interorganizational processes. Apart from technological issues that need to be addressed, it is important that all parties involved in such processes agree on the "rules of engagement". Therefore, we propose to use a contract that specifies the composition of the public views of all participating parties. Each party may then implement its part of the contract such that the implementation (i.e., the private view) accords with the contract. In this paper, we define a suitable notion of accordance inspired by the asynchronous nature of services. Moreover, we present several transformation rules for incrementally building a private view such that accordance with the contract is guaranteed by construction. These rules include adding internal tasks as well as the reordering of messages and are therefore much more powerful than existing correctness-preserving construction rules.

Dieter K�nig, Niels Lohmann, Simon Moser, Christian Stahl, and Karsten Wolf. Extending the Compatibility Notion for Abstract WS-BPEL Processes. In Wei-Ying Ma, Andrew Tomkins, and Xiaodong Zhang, editors, Proceedings of the 17th International Conference on World Wide Web, WWW 2008, Beijing, China, April 21--25, 2008, pages 785-794, April 2008. ACM.

Abstract: WS-BPEL defines a standard for executable business processes. Executable processes are business processes which can be automated through an IT infrastructure. The WS-BPEL specification also introduces the concept of abstract processes: In contrast to their executable siblings, abstract processes are not executable and can have parts where business logic is disguised. Nevertheless, the WS-BPEL specification introduces a notion of compatibility between such an under-specified abstract process and a fully specified executable one. Basically, this compatibility notion defines a set of syntactical rules that can be augmented or restricted by profiles. So far, there exists two of such profiles: the Abstract Process Profile for Observable Behavior and the Abstract Process Profile for Templates. None of these profiles defines a concept of behavioral equivalence. Therefore, both profiles are too strict with respect to the rules they impose when deciding whether an executable process is compatible to an abstract one. In this paper, we propose a novel profile that extends the existing Abstract Process Profile for Observable Behavior by defining a behavioral relationship. We also show that our novel profile allows for more flexibility when deciding whether an executable and an abstract process are compatible.

Wolfgang Reisig, Dirk Fahland, Niels Lohmann, Peter Massuthe, Christian Stahl, Daniela Weinberg, Karsten Wolf, and Kathrin Kaschner. Analysis Techniques for Service Models. In Second International Symposium on Leveraging Applications of Formal Methods, Verification and Validation, 2006 (ISoLA 2006), 15-19 November 2006, Paphos, Cyprus, pages 11-17, November 2006. IEEE Computer Society.

Abstract: The paradigm of Service-Oriented Computing (SOC) provides a framework for interorganizational business processes and for the emerging programming-in-the-large. The basic idea of SOC, the interaction of services, rises a lot of issues such as proper termination of interacting services or substitution of a service by another one. Such issues can be addressed by means of models of services. We show how services can intelligibly be modeled, and we present algorithms and tools to analyze properties of service models. To make sure that our models properly reflect real world issues of services, we model and investigate services represented in established languages such as WS-BPEL.

Technische Berichte

Christian Stahl, Peter Massuthe, and Jan Bretschneider. Deciding Substitutability of Services with Operating Guidelines. Informatik-Berichte 222, Humboldt-Universit�t zu Berlin, April 2008.

Abstract: Deciding whether a service $S$ can be substituted by another service S' is an important problem in practice and one of the research challenges in service-oriented computing. In this paper, we define three substitutability notions for services. Accordance specifies that S' cooperates with at least the environments that S cooperates with. S and S' are equivalent if they cooperate with the same environments. To guarantee that S' cooperates with a fixed subset of environments that S cooperates with, the notion of deprecation can be used. For each substitutability notion we present a decision algorithm. To this end we apply the concept of an operating guideline of a service as an abstract representation of all environments the service cooperates with.

Wil M. P. van der Aalst, Peter Massuthe, Arjan J. Mooij, Christian Stahl, and Karsten Wolf. Erratum -- Multiparty Contracts: Agreeing and Implementing Interorganizational Processes. Informatik-Berichte 213, Humboldt-Universit�t zu Berlin, June 2007.

Wil M. P. van der Aalst, Peter Massuthe, Christian Stahl, and Karsten Wolf. Multiparty Contracts: Agreeing and Implementing Interorganizational Processes. Informatik-Berichte 213, Humboldt-Universit�t zu Berlin, June 2007. Note: There is an erratum.

Abstract: A contract specifies an interorganizational process together with a distribution of responsibilities for the activities among the parties involved. In this paper, we formally show how a party can implement its part of the contract such that the implementation accords with the contract. We propose a formal notion of a contract and give a criterion for accordance between a local implementation and a contract such that, if all local implementations accord with the contract, the overall process is deadlock-free and it is always possible to terminate properly. Then, we sketch a technique for automatically checking the proposed accordance criterion. Finally, we present accordance-preserving transformation rules. These rules can be used to implement a part of the contract while preserving the accordance criterion.

Dieter K�nig, Niels Lohmann, Simon Moser, Christian Stahl, and Karsten Wolf. Extending the Compatibility Notion for Abstract WS-BPEL Processes. Preprint CS-02-07, Universit�t Rostock, Rostock, Germany, November 2007.

Abstract: WS-BPEL defines a standard for executable business processes. Executable processes are business processes which can be automated through an IT infrastructure. The WS-BPEL specification also introduces the concept of abstract processes: In contrast to their executable siblings, abstract processes are not executable and can have parts where business logic is disguised. Nevertheless, the WS-BPEL specification introduces a notion of compatibility between such an under-specified abstract process and a fully specified executable one. Basically, this compatibility notion defines a set of syntactical rules that can be augmented or restricted by profiles. So far, there exists two of such profiles: the Abstract Process Profile for Observable Behavior and the Abstract Process Profile for Templates. None of these profiles defines a concept of behavioral equivalence. Therefore, both profiles are too strict with respect to the rules they impose when deciding whether an executable process is compatible to an abstract one. In this paper, we propose a novel profile that extends the existing Abstract Process Profile for Observable Behavior by defining a behavioral relationship. We also show that our novel profile allows for more flexibility when deciding whether an executable and an abstract process are compatible.

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