Gurevich's sequential Abstract State Machines (ASMs)are taken as a basis for the construction of distributed ASMs as sets of sequential ASMs. A theorem on the expressive power of distributed ASMs is proven in analogy to Gurevich's classical theorem on the expressive power of sequential ASMs.

Conventional computational models assume a symbolical representation of states. Gurevich's Abstract State Machines (ASMs) take a more liberal position: any mathematical structure may serve as a state. Gurevich characterizes the expressive power of sequential ASMs in a non-trivial theorem: he defines the class of \emphsequential algorithms by help of only a few, amazingly general requirements and proves this class to be equivalent to sequential ASMs. Later, this result has been extended to the class of bounded-nondeterministic ASMs. This paper considers the general case of unbounded-nondeterministic ASMs: in each step, an unbounded-nondeterministic ASM may choose among infinitely many alternatives. We define the class of unbounded-nondeterministic algorithms by a conservative extension of Gurevich's original requirements to sequential algorithms. We show that this class is equivalent to unbounded-nondeterministic ASMs.

In 1985, Gurevich introduced Abstract State Machines (ASMs) as a computational model more powerful and universal than classical computational models. Since then ASMs have been applied successfully both in theory and practice: On the theoretical side, ASMs evolved to a general basis for the study of different classes of algorithms and their expressive power. On the practical side, ASMs have been extended to a full-fledged design methodology, applied successfully in industry for the specification and analysis of real-world systems. In my doctoral thesis I examine the class of distributed ASMs and study their expressive power. I also intend to develop basic notions of refinement and composition for distributed ASMs.

Wir untersuchen die Ausdrucksmächtigkeit von Petrinetz-Schemata. Dazuführen wir die Teilklasse der einfachen Petrinetz-Schemata ein und zeigen, welche Systeme sich durch ein einfaches Petrinetz-Schema darstellen lassen und welche nicht. Die hinreichenden und notwendigen Eigenschaften dazu formulieren wir in einem Theorem.

Abstract-State-Machines, kurz ASMs, sind eine Methode zur formalen Beschreibung von Algorithmen. Diese Methode hebt sich dabei deutlich von klassischen Algorithmusbegriffen wie Turingmaschinen und berechenbaren Funktionen ab. So lassen sich mit ASMs unter anderem auch nicht-terminierende Algorithmen beschreiben. Genauso wie es unterschiedliche Klassen von Algorithmen gibt, existieren auch eine ganze Reihe unterschiedlicher Klassen von ASMs, so zum Beispiel die sequentiellen, die nichtdeterministischen und die verteilten ASMs. Für die Klasse der sequentiellen ASMs exisitiert eine schöne Charakterisierung durch das sogenannte ASM-Theorem. Diese Charakterisierung basiert auf natürlichen und leicht verständlichen Forderungen und erleichtert somit dass Verständnis für die Ausdrucksmächtigkeit der sequentiellen ASMs und von Algorithmen im Allgemeinen. In dieser Arbeit erweitern wir das ASM-Theorem auf die Klasse der nichtdeterministischen ASMs und auf die Klasse der verteilten ASMs.

Diese Studienarbeit versucht durch eine Vielzahl von Beispielen den Begriff Abstract-State Machine und sequenzieller Algorithmus didaktisch sinnvoll darzustellen. Es werden dabei sowohl Beispiele als auch Gegenbeispiele angegeben, um Umfang und Grenzen dieser Begriffe aufzuzeigen.

Service-oriented computing aims to create complex systems by composing less-complex systems, called services. Since services can be developed independently, the integration of services requires an adaptation mechanism for bridging any incompatibilities. Behavioral adapters aim to adjust the communication between some services to be composed in order to establish proper interaction between them. We present a novel approach for specifying such adapters, based on domain-specific transformation rules that reflect the elementary operations that adapters can perform. We also present a novel way to synthesize complex adapters that adhere to these rules, viz., by consistently separating data and control, and by using existing controller-synthesis algorithms. Our approach has been implemented, and we discuss some example applications, including real business processes in WS-BPEL.

In dieser Arbeit werden wir uns mit Diamantenstrukturen in Bedienungsanleitungen beschäftigen. Im Rahmen der Service-Oriented Architecture beschreiben Bedienungsanleitungen Kommunikationspartner (Strategien) von Diensten. Ein großer Vorteil der Bedienungsanleitungen ist die endliche Repräsentation der gewöhnlich unendlich großen Menge aller Strategien eines Dienstes. Bedienungsanleitungen können nichtsdestotrotz sehr groß werden. Diamantenstrukturen sind eine der Hauptursachen dafür. Wir wollen eine Kurzschreibweise einführen, die das Eintreten von Ereignissen in jeder beliebigen Reihenfolge in einem Zustandsübergang beschreibt. Anschließend werden wir verschiedene Muster für Diamantenstrukturen vorstellen, also Muster mit Ereignissen, die in jeder beliebigen Reihenfolge stattfinden können. Für diese Muster werden wir Ersetzungen mit der eingeführten Kurzschreibweise angeben. Wir werden ferner Algorithmen angeben, welche die von uns definierten Diamantenmuster in Bedienungsanleitungen erkennen.

Behavioral adapters are a way to establish proper interaction between services that have been developed independently. We present a novel approach for specifying such adapters, based on domain-specific transformation rules that reflect the elementary operations that adapters can perform. We show how complex adapters that adhere to these rules can be generated using existing controller generation algorithms. We discuss some example applications, including real-world business processes.

In der Welt der Service Orientierten Architektur (SOA) besteht der Bedarf, Dienste auf ihre mögliche Interaktion mit anderen Diensten hin zu untersuchen. Dienste werden wir in Form von Serviceautomaten betrachten, die als asynchron kommunizierende Automaten definiert sind. Um die Frage einer sinnvollen, also verklemmungsfreien Kommunikation zu klären, gibt es das Konzept der Bedienungsanleitungen. Wie werden für diese ein scharfes Kriterium für die Wahl der Endzustände angeben und zeigen, dass diese Wahl sich in vorhandene Konzepte integriert. Besonderes Augenmerk werden wir dabei auf den Liberalsten Partner und den Public View eines Serviceautomaten werfen und an diesen unsere Definition rechtfertigen.

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.

The accordance pre-order describes whether a service can safely be replaced by another service. That is, all partners for the original service should be partners for the new service. Partners for a service interact with the service in such a way that always a certain common goal can be reached. We relate the accordance pre-order to the pre-orders known from the linear-branching time spectrum, notably fair testing. The differences between accordance and fair testing include the modeling of termination and success, and the parts of the services that cannot be used reliably by any partner. Apart from the theoretical results, we address the practical relevance of the introduced concepts.

In a service-oriented architecture (SOA), a service broker assigns a previously published service (stored in a service registry) to a service requester. It is desirable for the composition of the requesting and the assigned service to interact properly. While proper interaction is often reduced to deadlock freedom of the composed system, we additionally consider livelock freedom as a desirable property for the interaction of services. In principle, deadlock- and livelock freedom can be verified by inspecting the state space of the composition of (public views of) the involved services. The contribution of this paper is to propose a methodology to build that state space from pre-computed fragments which are computed upon publishing a service. That way, we shift computation time from the time critical request phase of service brokerage to the less critical publish phase. Interestingly, our setting enables state space reduction methods that are intrinsically different from traditional state space reductions.

Services change over time, be it for internal improvements, be it for external requirements such as new legal regulations. For long running services, it may even be necessary to change a service while instances are actually running and interacting with other services. This problem is referred to as instance migration. We present a novel approach to the behavioral (service protocol) aspects of instance migration. We apply techniques for finitely characterizing the set of all correctly interacting partners to a given service. The approach assures that migration does not introduce behavioral problems with any running partner of the original service. Our technique scales up to services with thousands of states, including models of real WS-BPEL processes.

We compare two Petri net semantics for the Web Services Business Process Execution Language (BPEL). The comparison reveals different modelling decisions. These decisions together with their consequences are discussed. We also give an overview of the different properties that can be verified on the resulting models. A case study helps to evaluate the corresponding compilers which transform a BPEL process into a Petri net model.

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.

In this paper, we present a framework that allows us to orchestrate web services such that the web services involved in this orchestration interact properly. To achieve this, we predefine service interfaces and certain routing constructs. Furthermore, we define a number of rules to incrementally compute the price of such a properly interacting orchestration (i.e. a web service) from the price of its web services. The fact that a web service gets only payed after its service is delivered (no-cure-no-pay) is reflected by considering a probability of success. To determine a safe price that includes the risk a web service takes, we consider the variance of costs.

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?

Service-Oriented Computing is an emerging computing paradigm that supports the modular design of (software) systems. Complex systems are designed by composing less complex systems, called services. Such a (complex) system is a distributed application often involving several cooperating enterprises. As a system usually changes over time, individual services will be substituted by other services. Substituting one service by another one should not affect the correctness of the overall system. Assuring correctness becomes particularly challenging, as the services rely on each other, and each of the involved enterprises only oversees a part of the overall system. In addition, services communicate asynchronously which makes the analysis even more difficult. For this reason, formal methods to support service substitution are indispensable. In this thesis, we study service substitution at the level of service models. Thereby we restrict ourselves to service behavior. As a formalism to model service behavior, we use Petri nets. The first contribution of this thesis is the definition of several substitutability criteria that are suitable in the context of Service-Oriented Computing. Substituting a service S by a service S' should preserve some behavioral properties of the overall system. For each set of behavioral properties and a given service S, there exists a set of behaviorally compatible services for S. A substitutability criterion defines which of these behaviorally compatible services of S have to be preserved by S'. We relate our substitutability criteria to preorders and equivalences known from process theory. The second contribution of this thesis is to present, for each substitutability criterion, a procedure to decide whether a service S' can substitute a service S. The decision requires the comparison of the in general infinite sets of behaviorally compatible services for the services S and S'. Hence, we extend existing work on an abstract representation of all behaviorally compatible services for a given service. For each notion of behavioral compatibility, we present an algorithmic solution to represent all behaviorally compatible services. Based on these representations, we can decide substitutability of a service S by a service S'. The third contribution of this thesis is a method to support the design of a service S' that can substitute a service $S$ according to a substitutability criterion. Our approach is to derive a service S' from the service S by stepwise transformation. To this end, we present several transformation rules. Finally, we formalize and we extend the equivalence notion for services specified in the language WS-BPEL. That way, we demonstrate the applicability of our work.

We address the problem of analyzing the interaction between WS-BPEL processes. We present a technology chain that starts out with a WS-BPEL process and translates it into a Petri net model. On the model we decide controllability of the process (the existence of a partner process, such that both can interact properly) and compute its operating guideline (a characterization of all properly interacting partner processes). To manage processes of realistic size, we present a concept of a \emphflexible model generation which allows the generation of compact Petri net models. A case study demonstrates the value of this technology chain.

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.

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.

In this paper, we present a framework that allows us to orchestrate web services such that the web services involved in this orchestration interact properly. To achieve this, we predefine service interfaces and certain routing constructs. Furthermore, we define a number of rules to incrementally compute the price of such a properly interacting orchestration (i.e. a web service) from the price of its web services. The fact that a web service gets only payed after its service is delivered (no-cure-no-pay) is reflected by considering a probability of success. To determine a safe price that includes the risk a web service takes, we consider the variance of costs.

In this paper we propose a framework for SOA covering such important features as proper termination (soundness) and correct correlation of tasks. Within this framework, we define a method for the calculation of the price of services. Our framework is compositional in the sense that composing a system from subsystems that meet our correctness requirements we obtain a system that still meets these requirements.

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.

We compare two Petri net semantics for the Web Services Business Process Execution Language (BPEL). The comparison reveals different modeling decisions. These decisions together with their consequences are discussed.We also give an overview of the different properties that can be verified on the resulting models. A case study helps to evaluate the corresponding compilers which transform a BPEL process into a Petri net model.

We present an Service-Oriented Architecture (SOA)-based architecture framework. The architecture framework is designed to be close to industry standards, especially to the Service ComponentArchitecture (SCA).The framework is language independent and the building blocks of each system, activities and data, are first class citizens.We present a meta model of the architecture framework and discuss its concepts in detail. Through the framework, concepts of an SOA such as wiring, correlation and instantiation can be clarified.

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.

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.

We present a SOA-based architecture framework. The architecture framework is designed to be close to industry standards, especially to the Service Component Architecture (SCA). The framework is language independent and the building blocks of each system, activities and data, are first class citizens. We present a \emphmeta model of the architecture framework and discuss its concepts in detail. Through the framework concepts such as wiring, correlation, and instantiation can be clarified. This allows us to demystify some of the confusion related to SOA.

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.

In this paper we present first results of a SOA-based architecture framework. The architecture framework is required to be close to industry standards, especially to service component architecture (SCA), language independent (i.e. it is adoptable) and the building blocks of each system, activities and data, are first class citizens. We present a meta model of the architecture framework and discuss its concepts in detail.

A novel request-driven globally asynchronous locally synchronous (GALS) technique for the system integration of complex digital blocks is proposed. For this new GALS technique, an asynchronous wrapper compliant is developed and evaluated. This proposed GALS technique is applied to a baseband processor compatible with the wireless LAN standard IEEE 802.11a. The developed GALS baseband processor chip is fabricated and measured. Besides improvements of the system integration process, a 5 dB reduction in electromagnetic interference, 30\% reduction in instantaneous supply current variation, and similar dynamic power consumption as in the synchronous baseband processor is achieved.

Zur adäquaten Nutzung von Workflow-Implementierungen kommunizierender Geschäftsprozesse werden Konzepte vorgeschlagen,die von konkreten Implementierungen abstrahieren. Auf der Basis von Petrinetzen werden unterschiedliche Varianten der Bedienbarkeit von Workflows charakterisiert und dafür Entscheidungsalgorithmen vorgestellt. Die Angemessenheit des Ansatzes wird am Beispiel der Semantik von Komponenten der Geschäftsprozess-Modellierungssprache BPEL demonstriert.

We present a pattern-based Petri net semantics for the Business Process Execution Language for Web Services (BPEL). Our semantics is complete - it covers the standard behaviour of BPEL as well as the exceptional behav-iour (e.g. faults, events, compensation). Therefore every business process specified in BPEL can be transformed into a Petri net.

An asynchronous wrapper of a fabricated GALS system is analyzed for hazards. For this purpose a Petri net based modelling approach of this GALS wrapper is presented. In our model the question whether a hazard can occur in a gate is reduced to a model checking problem: the reachability of a particular marking in the Petri net. In order to alleviate state space explosion three techniques to reduce the model?s state space are presented. By use of these techniques we detected several potential hazards in the wrapper.

A Globally Asynchronous - Locally Synchronous (GALS) technique for application in wireless communication systems is proposed and evaluated. The GALS wrappers are based on a request-driven operation with an embedded time-out function. A formally verified GALS wrapper is deployed for the ?GALSification? of a baseband processor for WLAN. Details of the GALS partitioning, implementation and the design-flow are discussed. Furthermore, a test strategy based on built-in self-test (BIST) is suggested. The described baseband processor was fabricated and successfully tested. The GALS design is compared with a clock-gated, synchronous version. Advantages for system integration are achieved along with a 1% reduction in dynamic power consumption, a 30% reduction in peak power supply current, and 5 dB reduction in spectral noise.

An asynchronous wrapper of a fabricated GALS system is analyzed for hazards. For this purpose a Petri net based modelling approach of this GALS wrapper is presented. In our model the question whether a hazard can occur in a gate is reduced to a model checking problem: the reachability of a particular marking in the Petri net. In order to alleviate state space explosion two techniques to reduce the model's state space are presented. By use of these techniques we detected several potential hazards and a deadlock in the wrapper.

Verteilte Geschäftsprozesse nutzen das Internet, um auf heterogenen Rechnerstrukturen Dienste auszubieten. Modellierungstechniken und Implementierungssprachen für solche Dienste werfen im Vergleich mit herkömmlichen Rechnern grundlegend neue Fragestellungen auf. Wir diskutieren einige davon und zeigen, wie Petrinetze ihre Beantwortung ermöglichen.

We translated a small business process into a recently defined Petri net semantic. Then we used the tool LoLA for validating the semantic as well as for proving relevant properties of the particular process.

Moderne Systeme der Informationstechnik bestehen zumeist aus einer Vielzahl von Komponenten, die in einem Netzwerk auf verteilten Knoten ausgeführt werden. Mit dem Web-Service-Ansatz können solche Systeme einfacher und flexibler entwickelt werden. Diese Arbeit befasst sich mit der Modellierung, Visualisierung und Analyse von Web Services. Ein Web Service kapselt eine Anwendung und stellt diese über ein wohldefiniertes Interface der Außenwelt zur Verfügung. Im Gegensatz zu früheren Ansätzen dienen eine Reihe zusammenhängender Technologien zur Beschreibung eines Web Service. Diese Arbeit beschäftigt sich vor allem mit der internen Struktur eines Web Service, beschrieben mit Hilfe der Business Process Execution Language for Web Services (BPEL4WS) [ACD+02]. Der Web-Service-Ansatz bietet ein homogenes Konzept von Komponenten und ihrer Komposition ber einem heterogenen Netzwerk. Damit ist die syntaktische Grundlage für die Entwicklung verteilter Systeme gelegt. Wesentlich für den Erfolg der Web Services ist jedoch die Beantwortung der semantischen Fragestellungen: Passen zwei gegebene Web Services inhaltlich zusammen? Kann in einem verteilten System ein gegebener Web Service durch einen anderen ersetzt werden? Entspricht ein konkreter Web Service einer gegebenen abstrakten Spezifikation? Diese Arbeit befasst sich mit der Beantwortung dieser und weiterer Fragestellungen im Web-Service-Ansatz: In einem ersten Schritt entwickeln wir eine formale Semantik für die Sprache BPEL4WS. Darauf aufbauend werden Methoden zur Analyse verteilter Systeme auf die konkreten Anforderungen bertragen und neue Verfahren entwickelt. Für die Diskussion der Modelle und Eigenschaften entwickeln wir eine intuitive graphische Repräsentation der Sprache BPEL4WS. Das Ziel der Forschungen ist die Umsetzung der Methoden in einem integrierten Entwicklungswerkzeug für BPEL4WS. Die vorliegende Arbeit beschreibt die ersten Ergebnisse in einem laufenden Projekt.

BPEL4WS ist eine Sprache zur Beschreibung verteilter Geschäftsprozesse mit Web Services. Es besteht die Notwendigkeit, die Sprache trotz ihrer Komplexität zu verstehen, um mit ihr im Umfeld von Web Services arbeiten zu können. Mit Hilfe einer formalen Semantik ist es möglich, die Sprache selbst und mit BPEL4WS spezifizierte Geschäftsprozesse zu verifizieren. In der vorliegenden Arbeit wird eine Petrinetz-Semantik für BPEL4WS vorgestellt. Dazu wird gezeigt, dass jedes Konstrukt der Sprache BPEL4WS in ein Petrinetz-Muster übersetzt werden kann. Damit ist es möglich, jeden in der Geschäftsprozesssprache BPEL4WS modellierten Geschäftsprozess in ein Petrinetz zu transformieren. Bei der Entwicklung der Semantik kann auf Forschungsergebnisse aus dem Bereich "Petrinetze als Werkzeug zur Geschäftsprozessmodellierung" zurückgegriffen werden.

Industry and researchers have two different visions for the future of Web services. Industry wants to capitalize on Web service technology to automate business processes via centralized workflow enactment. Researchers are interested in the dynamic composition of Web services. The authors show how these two visions are points in a continuum and discuss a possible path for bridging the gap between them.

Verteilte Systeme haben in den letzten Jahren in der Informatik immer mehr an Bedeutung gewonnen. Die Web-Service-Architektur ist eine Software-Architektur zur Modellierung und Implementierung verteilter Systeme. Sie ist als eine der zukunftsträchtigsten Technologien angesehen, die aber noch in der Erprobungsphase steckt. Unter anderem ist die Kompatibilität von Web Services eine offene Frage, wobei weniger syntaktische als vielmehr sematischen Kompatibilität problematisch ist. Diese Arbeit soll Ansätze zur Bestimmung semantischer Kompatibilität von Web Services liefern.

We address the problem of analyzing the interaction between WS-BPEL processes. We present a technology chain that starts out with a WS-BPEL process and translates it into a Petri net model. On the model we decide controllability of the process (the existence of a partner process, such that both can interact properly) and compute its operating guideline (a characterization of all properly interacting partner processes). To manage processes of realistic size, we present a concept of a \emphflexible model generation which allows the generation of compact Petri net models. A case study demonstrates the value of this technology chain.

A service is designed to interact with other services. If the service interaction is stateful and asynchronous, the interaction protocol can become quite complex. A service may be able to interact with a lot of possible partner services, one partner or no partner at all. Having no partner surely is not intended by the designer. But the stateful interaction between services can be formalized and thus analyzed at design time. We present a formalization which is centered around a graph data structure that we call interaction graph, which represents feasible runs of a partner service according to the interaction protocol. As interaction graphs suffer from state explosion, we introduce a set of suitable reduction rules to alleviate the complexity of our approach. As our case studies show we are able to analyze the interaction behavior of a service efficiently.

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.

The internet today has grown to be more than just being a basis for exchanging information. It steadily becomes a platform for processing business processes. Many companies distribute their service with the help of web services or integrate other web services into their own workflow. However, before a web service gets published it should be examined well. We will introduce a way of examining the controllability of a web service. That means, we study whether a controller can actually use the functionality provided by the web service. We propose the interaction graph of a web service, that is modelled by an open workflow net. To verify whether such a net is controllable or not it is sufficient to construct a reduced interaction graph. We will define reduction rules that minimize the size of the graph greatly. The analysis using the interaction graph as well as the reduction rules shown in this paper are implemented and have been integrated into an analysis tool kit for web services.

Code generators are increasingly used in an industrial context to translate graphical models into executable code. Since the code is often deployed in safety-related environments, the quality of the code generators is of paramount importance. In this paper, we will present and discuss state-of-the-art techniques for safeguarding automatic code generation applied in model-based development.

The internet today has grown to be more than just being a basisfor exchanging information. It steadily becomes a platform for processing business processes. Many companies distribute their service with the help of web services or integrate other web services into their own workflow. However, before a web service gets published it should be examined well. We will introduce a way of examining the controllability of a web service. We propose the interaction graph of a web service, that is modelled by an open workflow net. To verify whether such a net is controllable or not it is sufficient to construct a reduced interaction graph. We will define reduction rules that minimize the size of the graph greatly. The analysis using the interaction graph as well as the reduction rules are implemented and have been integrated into an analysis tool kit for web services.

Das heutige Internet wächst zunehmend von einer Plattform als Informationsquelle hin zu einer Basis für die Abwicklung von Geschäftsprozessen. Zahlreiche Firmen stellen ihre Dienste bereits mit Hilfe von Web-Services zur Verfügung oder integrieren andere bereitgestellte Web-Services in ihren Geschäftsablauf. Nach Studien einiger Forschungsinstitute geht der Trend in der heutigen IT-Branche stark zum Einsatz solcher verteilter Geschäftsprozesse. Es werden Schlagworte wie out-tasking, plug-and-play und Lego-Wirtschaft geprägt. Bevor ein Geschäftsprozess in Form eines Web-Services jedoch veröffentlicht wird, sollte dieser geeignet untersucht werden. Wir werden uns in dieser Arbeit diesem Thema mit Hilfe von Petri-Netz-Modulen nähern. Sie modellieren gerade die interne Struktur von Geschäftsprozessen und ermöglichen es, den Prozess geeignet zu analysieren. Uns interessiert bei der Analyse, ob die Funktionalität, die ein Web-Service bereitstellen soll, auch wirklich genutzt werden kann. Wir sprechen in diesem Zusammenhang von Bedienbarkeit. Für die Analyse definieren wir den Interaktionsgraphen eines Workflow-Moduls, welcher die Zustände des Moduls und dessen Interaktion mit einer Umgebung veranschaulicht. Auf dieser Grundlage können wir dann eine Bedienstrategie definieren, durch die das Modul bedient werden kann. Das hei¼t, wenn eine Umgebung das Modul so bedienen kann, dass dieses ordentlich terminiert, finden wir eine Bedienstrategie in dem Interaktionsgraphen des Moduls. Darüber hinaus bieten die Graphen dem Modellierer die Möglichkeit, einen Blick auf die Abläufe seines Moduls zu werfen und genau erkennen zu können, welche Zustände des Moduls bei welcher Interaktion mit der Umgebung eingenommen werden. Auf Grundlage dieser Analyse kann der Modellierer seinen Prozess überarbeiten, anpassen etc. Um die Bedienbarkeit der Workflow-Module durch den Interaktionsgraphen zu verifizieren, reicht es aus, einen reduzierten Graphen zu konstruieren. Wir werden Reduktionsregeln definieren, die den Nachweis der Bedienbarkeit in den reduzierten Graphen erhalten. Die in dieser Arbeit entwickelten Algorithmen sind implementiert und in Wombat4ws, einem Analysewerkzeug für Web-Services, integriert worden.

Moderne Systeme der Informationstechnik bestehen zumeist aus einer Vielzahl von Komponenten, die in einem Netzwerk auf verteilten Knoten ausgeführt werden. Mit dem Web-Service-Ansatz können solche Systeme einfacher und flexibler entwickelt werden. Diese Arbeit befasst sich mit der Modellierung, Visualisierung und Analyse von Web Services. Ein Web Service kapselt eine Anwendung und stellt diese über ein wohldefiniertes Interface der Außenwelt zur Verfügung. Im Gegensatz zu früheren Ansätzen dienen eine Reihe zusammenhängender Technologien zur Beschreibung eines Web Service. Diese Arbeit beschäftigt sich vor allem mit der internen Struktur eines Web Service, beschrieben mit Hilfe der Business Process Execution Language for Web Services (BPEL4WS) [ACD+02]. Der Web-Service-Ansatz bietet ein homogenes Konzept von Komponenten und ihrer Komposition ber einem heterogenen Netzwerk. Damit ist die syntaktische Grundlage für die Entwicklung verteilter Systeme gelegt. Wesentlich für den Erfolg der Web Services ist jedoch die Beantwortung der semantischen Fragestellungen: Passen zwei gegebene Web Services inhaltlich zusammen? Kann in einem verteilten System ein gegebener Web Service durch einen anderen ersetzt werden? Entspricht ein konkreter Web Service einer gegebenen abstrakten Spezifikation? Diese Arbeit befasst sich mit der Beantwortung dieser und weiterer Fragestellungen im Web-Service-Ansatz: In einem ersten Schritt entwickeln wir eine formale Semantik für die Sprache BPEL4WS. Darauf aufbauend werden Methoden zur Analyse verteilter Systeme auf die konkreten Anforderungen bertragen und neue Verfahren entwickelt. Für die Diskussion der Modelle und Eigenschaften entwickeln wir eine intuitive graphische Repräsentation der Sprache BPEL4WS. Das Ziel der Forschungen ist die Umsetzung der Methoden in einem integrierten Entwicklungswerkzeug für BPEL4WS. Die vorliegende Arbeit beschreibt die ersten Ergebnisse in einem laufenden Projekt.

Modeling business processes has become a common activity in industry, but it is increasingly carried out by non-experts. This raises a challenge: How to ensure that the resulting process models are of sufficient quality? This paper contends that a prior structuring of domain knowledge, as found in informal specifications, will positively influence the act of process modeling in various measures of performance. This idea is tested and confirmed with a controlled experiment, which involved 83 master students in business administration and industrial engineering from Humboldt-Universität zu Berlin and Eindhoven University of Technology. In line with the reported findings, our recommendation is to explore ways to bring more structure in the specifications that are used as input for process modeling endeavors.

We present a formal semantics for a variant of UML2 Activity Diagrams that is used in the IBM WebSphere Business Modeler for modeling business processes. Business process models created in the IBM WebSphere Business Modeler or with other UML2 modeling tools often constitutes one of the key specification artifacts for building an information system that implements or supports the specified processes. As UML2 Activity Diagrams lack a universally agreed semantics, the step from specification to implementation usually faces a semantical impedance caused by different interpretation of the same diagram. A well-defined formal semantics for the specification language determines the interpretation of a diagram and allows for reasoning about as well as validating and verifying a given specification on common (formal) grounds. We adapt approaches for formalizing semantics of UML2 Activity Diagrams and apply them to the core features of the IBM WebSphere Business Modeler language for purpose of formal verification. We provide a parameterized Petri net pattern for each language concepts. A diagram is translated by instantiating a pattern for each use of a concept; merging the resulting Petri net fragments according to the structure of the original diagram yields a Petri net that specifies the behavioral semantics of the diagram. The resulting Petri net can be verified for control-flow errors using the model checker LoLA. The semantics has been implemented in a tool that is available at http://www.service-technology.org/uml2owfn/.

Usually, a component in a distributed system has assumptions about the remaining components of the system. A change in one component might require to change other components as well. It may happen that the change has to be performed in the running system. In this paper, we propose a formal model for systems that change their behavior at run-time: An adaptive system is denoted as a set of scenarios using a Petri net syntax. Our operational model provides an adaptation operator that synthesizes and adapts the system behavior as a Petri net branching-process at run-time based on the given scenarios. We show the feasibility of our approach by the help of an example.

In this paper we present a pattern-based approach for synthesizing truly distributed Petri nets from a class of LTL specifications. The synthesis allows for the automatic, correct generation of humanly conceivable Petri nets, thus circumventing a manual construction of nets, or the use of Büuchi automata which are not distributed and often less intuitive to understand.

The problem and need for adapting business processes and service behavior to cope with changing circumstances is identified well. Standard models for business processes still rely on a fixed process logic, the change of which is rather hard to achieve. Ad-hoc changes to a standard model are usually considered too `dangerous' as they are performed in not well-defined manner. Other models for adaptive processes deviate to some extent from established business process models. This deviation comes at the price of limited understandability and loss in analysis capabilities. We propose a model for adaptive processes based on Petri nets which have successfully been applied in modeling and analyzing business process and web services. Our operator to adapt the behavior of such models is formalized by the help of scenario-based concepts known from live-sequence charts in purely mathematical terms. This combination of concepts allows to write down the result of the adaptation rather than how adaptation shall be performed.

Enacting tasks in a workflow cannot always follow a pre-defined process model. In application domains like disaster management workflows are partially specified and circumstances of their enactment change. There exist various approaches for formal workflow models that are effective in such situations, like declarative specifications instead of operational models for formalizing flexible workflow process. These powerful models leave a gap to existing techniques in the domain of workflow modeling, workflow analysis, and workflow management. In this paper we bridge this gap with a compositional mechanism for translating declarative workflow models to operational workflow models. The mechanism is of a general nature and we reveal its principles as we provide an exemplary definition for translating DecSerFlow models based on LTL to Petri nets. We then demonstrate its use in analyzing and refining declarative models.

Fast and effective disaster management requires access to a multitude of heterogeneous, distributed, and quickly changing data sets, such as maps, satellite images, or governmental databases. In the last years, also the information created by affected persons on web sites such as flickr.com or blogger.com became an important and very quickly adapting source of information. We developed HUODINI, a prototype system for the flexible integration and visualization of heterogeneous data sources for disaster management. HUODINI is based on Semantic Web technologies, and in particular RDF, to offer maximal flexibility in the types of data sources it can integrate. It supports a hybrid push/pull approach to cater for the requirements of fast-changing sources, such as news feeds, and maximum performance for querying the integrated data set. In this paper, we describe the design goals underlying our approach, its architecture, and report on first experiences with the system.

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.

In this thesis we develop a state space reduction technique for networks of timed automata based on unfoldings to alleviate the state space explosion problem due to concurrently enabled actions. For the purpose of verifying a system, standard model checking techniques construct its sequential state space that suffers an exponential growth when applied to distributed systems because of concurrently enabled, independent actions: during the construction of the state space these actions are ordered arbitrarily to simulate concurrency in the sequential model. For untimed systems, state space reduction techniques like stubborn sets that omit the construction of redundant information, and unfoldings that represent concurrent events in a partial order have successfully been applied to alleviate the exponential growth. These techniques apply a simple syntactical criterion to identify independent actions. This criterion is not applicable to networks of timed automata as simple examples show, which renders the existing techniques unapplicable. But networks of timed automata face the state space explosion problem as well which raises the demand for a specific reduction technique for these systems. In this thesis, we consider a special, but practically relevant class of networks of timed automata as a formal model for discrete, distributed, timed systems. We develop a novel technique that constructs a complete, finite representation of such a system's state space. This representation is the complete, finite prefix of an unfolding in which concurrently enabled actions are partially ordered. We show that this technique is capable of reducing the size of the state space by magnitude. We are presently not aware of any state space reduction technique for timed automata with similar results.

In this technical report we present an abstract operational semantics for the Business ProcessExecution Language for Web Services, or BPEL for short. In effect, the semantics defined herein are a variation and an extension of the semantics published first in [FGV04a] and [Far04] defined by the group of Uwe Glässer the Simon Fraser University, Vancouver, Canada. We namely add semantics for correlation handling, dead path elimination and event handling; we define the data handling on a finer level; we slightly alter the basic framework of how activities are formalized in [FGV04a] in order to achieve greater robustness against changes of the informal specification. Furthermore this technical report serves as a base for a joint work with the group of Simon Fraser University.

BPEL is presently the most prominent language to specify and execute business processes, using Web Services as its technological basis. Particular problems arise when activities are faulty: faults have to be propagated, other activities have to be irregularly terminated, etc. We describe the formal semantics of fault handlers and event handlers, demonstrating that ASMs are most adequate for this purpose.

In dieser Arbeit stellen wir einen Ansatz zur Definition einer formalen Semantik für die Business Process Execution Language for Web Services (kurz BPEL4WS) von IBM, Microsoft und deren Industriepartnern vor. Zur Formalisierung wählen wir den Abstract-State-Machine-Formalismus (kurz ASM), dessen theoretische Fundierung es uns erlaubt, die Semantik von BPEL4WS auf der selben Abstraktionsebene zur formalisieren, die in der informalen BPEL4WS-Spezifikation vorgegeben ist. Wir werden den inneren Aufbau der Sprache präzise, formal abbilden und damit eine intuitiv und anschaulich nachvollziehbare Entsprechung zwischen den Abläufen eines BPEL4WSProzesses gemäß der gegebenen informalen Semantik und unserer formalen Semantik aufzeigen. Dazu analysieren wir die Struktur von BPEL4WS und zeigen mit welchen Mitteln des ASM-Formalismus diese adäquat, formal erfasst werden und wie in ASM notierte Spezifikationen zu lesen sind. Hierzu werden wir beispielhaft ausgewählte, syntaktische Konstrukte von BPEL4WS nach unserem Ansatz formalisieren. Die vorliegende Arbeit bezieht sich auf die informale BPEL4WS-Spezifikation v1.1, veröffentlicht am 5. Mai 2003.

Moderne Systeme der Informationstechnik bestehen zumeist aus einer Vielzahl von Komponenten, die in einem Netzwerk auf verteilten Knoten ausgeführt werden. Mit dem Web-Service-Ansatz können solche Systeme einfacher und flexibler entwickelt werden. Diese Arbeit befasst sich mit der Modellierung, Visualisierung und Analyse von Web Services. Ein Web Service kapselt eine Anwendung und stellt diese über ein wohldefiniertes Interface der Außenwelt zur Verfügung. Im Gegensatz zu früheren Ansätzen dienen eine Reihe zusammenhängender Technologien zur Beschreibung eines Web Service. Diese Arbeit beschäftigt sich vor allem mit der internen Struktur eines Web Service, beschrieben mit Hilfe der Business Process Execution Language for Web Services (BPEL4WS) [ACD+02]. Der Web-Service-Ansatz bietet ein homogenes Konzept von Komponenten und ihrer Komposition ber einem heterogenen Netzwerk. Damit ist die syntaktische Grundlage für die Entwicklung verteilter Systeme gelegt. Wesentlich für den Erfolg der Web Services ist jedoch die Beantwortung der semantischen Fragestellungen: Passen zwei gegebene Web Services inhaltlich zusammen? Kann in einem verteilten System ein gegebener Web Service durch einen anderen ersetzt werden? Entspricht ein konkreter Web Service einer gegebenen abstrakten Spezifikation? Diese Arbeit befasst sich mit der Beantwortung dieser und weiterer Fragestellungen im Web-Service-Ansatz: In einem ersten Schritt entwickeln wir eine formale Semantik für die Sprache BPEL4WS. Darauf aufbauend werden Methoden zur Analyse verteilter Systeme auf die konkreten Anforderungen bertragen und neue Verfahren entwickelt. Für die Diskussion der Modelle und Eigenschaften entwickeln wir eine intuitive graphische Repräsentation der Sprache BPEL4WS. Das Ziel der Forschungen ist die Umsetzung der Methoden in einem integrierten Entwicklungswerkzeug für BPEL4WS. Die vorliegende Arbeit beschreibt die ersten Ergebnisse in einem laufenden Projekt.

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.

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.

Unternehmen sind bestrebt, immer mehr Geschäfte mit ihren Kunden teilweise oder vollständig automatisiert abzuwickeln. In diesem Bestreben machen sie mehr und mehr Gebrauch von der serviceorientierten Architektur (SOA). Grundbaustein der SOA ist der Service, der eine von einem Unternehmen angebotene Dienstleistung oder Funktionalität über eine wohldefinierte Schnittstelle bereitstellt und von Kunden oder Services anderer Unternehmen verwendet werden kann. Damit wir zwei Services als sinnvoll miteinander interagierend bezeichnen können, müssen sie verschiedene Mindestanforderungen erfüllen. Auf Grundlage dieser Mindestanforderungen können wir für jeden gegebenen Service eine Bedienungsanleitung konstruieren, die alle sinnvoll mit ihm interagierenden Services charakterisiert. Auch tritt die Frage auf, gegen welche Services ein Service ausgetauscht werden kann, so dass alle Services, die mit dem alten sinnvoll interagieren konnten, auch mit dem neuen sinnvoll interagieren können. Diesen allgemeinen Austauschbarkeitsbegriff parametrisieren wir in der vorliegenden Arbeit und beschäftigen uns mit dem Fall, dass durch den Austausch eines Services nur eine bestimmte Menge von Services unberührt bleiben soll, weil dies eine größere Freiheit in der Wahl des austauschenden Service erlaubt. Wir werden die Menge der Services, gegen die sich ein bestimmter Service bezüglich einer gegebenen Menge von Services austauschen lässt, mit Hilfe des Konzepts der Bedienungsanleitungen genau charakterisieren.

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.

Global asynchrone, lokal synchrone (GALS) Systeme vereinen dieVorteile synchroner und asynchroner Schaltungen und mindern zugleich ihre Nachteile. Ein GALS-System besteht aus mehreren lokal synchron arbeitenden Modulen, von denen jedes von einem asynchron arbeitenden Wrapper umhüllt wird. Durch diese Wrapper kommunizieren die Module asynchron miteinander. Das IHP Frankfurt hat auf Grundlage einer informalen Spezifikation einen GALS-Wrapper entwickelt. Erst nachträglich wurde ein formales Modell für diesen Wrapper erstellt und auf Korrektheit überprüft. Dabei wurden Fehler in der Implementierung gefunden und korrigiert. Wir beschreiben den Entwurf eines per Konstruktion korrekten Wrappers, der sich an der Schnittstelle zu seiner Umgebung genauso verhält, wie der Wrapper des IHP. Dazu modellieren wir erst sein Verhalten als Petrinetz und generieren danach aus diesem Modell mit dem Werkzeug petrify eine geschwindigkeitsinvariante Schaltung, die per Konstruktion korrekt arbeitet.

Die Web Services Business Process Execution Language ist eine Sprache zur Modellierung von Geschäftsprozessen als Web Services. Für eine umfassende Analyse von WS-BPEL-Prozessen müssen auch die Daten der Prozesse analysiert werden. Daten werden in WS-BPEL-Prozessen mit Hilfe von XML-Schema typisiert und standardmäßig mit Hilfe von XPath manipuliert. Eine Datenanalyse für WS-BPEL muss deshalb XML-Schema berücksichtigen die im Prozess enthaltenen XPath-Ausdrücke auswerten. Eine solche Datenanalyse ermöglicht Rückschlüsse auf den Kontrollfluss und dient so beispielsweise zur Optimierung eines WS-BPEL-Prozesses. In der vorliegenden Arbeit wird ein Verfahren zur abstrakten Interpetation von XPath-Ausdrücken in WS-BPEL-Prozessen vorgestellt. Dafür wird ein umfassendes Datenmodell für WS-BPEL-Prozesse sowie die enthaltenen XPath-Ausdrücke entwickelt. Auf Grundlage des entwickelten Datenmodells stellen wir eine statische Analyse vor, die die XPath-Ausdrücke in einem WS-BPEL-Prozess abstrakt interpretiert. Die Analyse berechnet dabei die Wertebereiche für Variablen und Bedingungen in WS-BPEL-Prozessen.

The Business Process Execution Language for Web Services WS-BPEL provides an technology to aggregate encapsulated functionalities for defining high-value Web services. For a distributed application in a B2B interaction, the partners simply need to expose their provided functionality as BPEL processes and compose them. Verifying such distributed web service based systems has been a huge topic in the research community lately - cf. [4] for a good overview. However, in most of the work on analyzing properties of interacting Web Services, especially when backed by stateful implementations like WS-BPEL, the data flow present in the implementation is widely neglected, and the analysis focusses on control flow only. This might lead to false-positive analysis results when searching for design weaknesses and errors, e.g. analyzing the controllability [14] of a given BPEL process. In this paper, we present a method to extract data flow information by constructing a CSSA representation and detecting data dependencies that effect communication behavior. Those discovered dependencies are used to construct a more precise formal model of the given BPEL process and hence to improve the quality of analysis results.

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.

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.