Christian Stahl

Eindhoven University of Technology | TUE · Section Information Systems (IS)

We study open systems modeled as Petri nets with an interface for asynchronous communication with other open systems. As a minimal requirement for successful communication, we investigate bounded responsiveness, which guarantees that an open system and its environment always have the possibility to mutually terminate or to communicate, while the nu...

We study asynchronously communicating open systems modeled as Petri nets with an interface. An accordance preorder describes when one open system can be safely replaced by another open system without affecting some behavioral property of the overall system. Although accordance is decidable for several behavioral properties if we assume a previously...

We study open systems modeled as Petri nets with an interface for asynchronous (i.e., buffered) communication with other open systems. As a minimal requirement for successful communication, we investigate responsiveness, which guarantees that an open system and its environment always have the possibility to communicate. We investigate responsivenes...

Process discovery techniques can be used to derive a process model from observed example behavior (i.e., an event log). As the observed behavior is inherently incomplete and models may serve different purposes, four competing quality dimensions—fitness, precision, simplicity, and generalization—have to be balanced to produce a process model of high...

Service-oriented design supports system evolution and encourages reuse and modularization. A key ingredient of service orientation is the ability to substitute one service by another without reconfiguring the overall system. This chapter aims to give an overview of the state of the art and open challenges in the area of service substitution. Thereb...

Declarative modeling has attracted much attention over the last years, resulting in the development of several academic declarative modeling techniques and tools. The absence of empirical evaluations on their use and usefulness, however, raises the question whether practitioners are attracted to using those techniques. In this paper, we present a s...

We investigate the verification of the soundness property for workflow nets (WF-nets) extended with resources, thereby considering the most general instance of soundness, which requires that, for any number of instances, the WF-net has always the possibility to terminate, for a certain initial (finite) number of resource items per resource type; mo...

Correctness of workflow design cannot be evaluated by checking the execution for one single instance of the workflow, because instances, even when being independent from the data perspective, depend on each other with respect to the resources they rely on for executing tasks. The resources are shared among the instances of the same workflow; moreov...

Colored Petri nets (CPNs) extend the classical Petri net formalism with data, time, and hierarchy. These extensions make it possible to model complex processes as CPNs without being forced to abstract from relevant aspects. Moreover, CPNs are supported by CPN tools – a powerful toolset that supports the design and analysis of such processes. The ex...

Grading dozens of Petri net models manually is a tedious and error-prone task. In this paper, we present Grade/CPN, a tool supporting the grading of Colored Petri nets modeled in CPN Tools. The tool is extensible, configurable, and can check static and dynamic properties. It automatically handles tedious tasks like checking that good modeling pract...

UnconstrainedMiner is a tool for fast and accurate mining Declare constraints from models without imposing any assumptions about the model. Declare models impose constraints instead of explicitly stating event orders. Constraints can impose various choices and ordering of events; constraints typically have understandable names, but for details, ref...

In the context of asynchronously communicating services, responsiveness guarantees that a service and its environment have always the possibility to communicate. The responsiveness preorder describes when one service can be replaced by another such that responsiveness is preserved. We study responsiveness for possibly unbounded services with and wi...

In the context of asynchronously communicating and deadlock free services, the refinement relation of services has been formalized by the accordance preorder. A service Impl accords with a service Spec if every controller of Spec-that is, every environment that can interact with service Spec without deadlocking-is a controller of Impl. The procedur...

We investigate whether a running implementation of a service conforms to its formal specification in a setting, where only recorded behavior of that implementation is given. Existing conformance checking techniques can be used to measure the degree of conformance of the recorded behavior and its public view but may produce “false negatives”, becaus...

Virtual assembly training systems show a high potential to complement or even replace physical setups for training of assembly processes in and beyond the automotive industry. The precondition for the breakthrough of virtual training is that it overcomes the problems of former approaches. The paper presents the design approach taken during the deve...

We revise the accordance preorder in the context of deadlock freedom for asynchronously communicating services. Accordance considers all controllers of a service—that is, all environments that can interact with the service without deadlocking. A service Impl accords with a service Spec if every controller of Spec is also a controller of Impl. We mo...

Grading dozens of Petri net models manually is a tedious and error-prone task. In this paper, we present Grade/CPN, a tool supporting the grading of Colored Petri nets modeled in CPN Tools. The tool is extensible, configurable, and can check static and dynamic properties. It automatically handles tedious tasks like checking that good modeling pract...

A conceptual workflow model specifies the control flow of a workflow together with abstract data information. This model is later on refined by adding specific data information, resulting in an executable workflow which is then run on an information system. It is desirable that correctness properties of the conceptual workflow are transferable to i...

Operating guidelines have been introduced to characterize all controllers for a given service S. A controller of S is a service that interacts with S without deadlocking. An operating guideline of S can be used to decide whether S refines another service. It is a special-purpose structure to describe the behavior of service S from the perspective o...

Service-oriented systems support process evolution by allowing the replacement of a service S by another service T. To maintain proper interaction in the overall system, service T should interact properly with all controllers (i.e., in all contexts) of service S. To support the construction of such services T, we compute operating guidelines that...

A big issue in the paradigm of Service Oriented Architectures (SOA) is service discovery. Organizations publish their services via the Internet. These published services can then be automatically found and accessed by other services, meaning, the services are composed. A fundamental property of a service composition is weak termination, which guara...

Service-oriented systems support process evolution by allow-ing the replacement of a service S by another service T . To maintain proper interaction in the overall system, service T should interact prop-erly with all controllers (i. e., in all contexts) of service S. To support the construction of such services T , we compute operating guidelines t...

A conceptual workflow model specifies the control flow of a workflow together with abstract data information. This model is later on refined to be executed on an information system. It is desirable that correctness properties of the conceptual workflow would be transferrable to its refinements. In this paper, we present classical workflow nets exte...

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 kn...

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 p...

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...

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 additio...

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...

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 orch...

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...

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 fo...

We present a finite representation of all services M where the composition with a given service N is deadlock-free, and a given set of activities of N can be covered (i.e. is not dead). Our representation is an extension of the existing notion of an operating guideline which only cared about deadlock freedom. We further present an algorithm to deci...

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 guide...

We calculate a fixed finite set of state space fragments for a service P, where each fragment carries a part of the whole behavior of P. By composing these fragments according to the behavior of a service R we build the state space of their composition P R which can be checked for deadlocks and livelocks. We show that this approach is applicable to...

WS-BPEL defines a standard for executable processes. Exe-cutable processes are business processes which can be auto-mated through an IT infrastructure. The WS-BPEL speci-fication 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...

Deciding whether a service S can be substituted by another service S0 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 S0 cooperates with at least the environments that S cooperates with. S and S0 are...

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 i...

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 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...

The recent success of service-oriented architectures gives rise to some fundamental questions: To what extent do services constitute a new paradigm of computation? What are the elementary ingredients of this paradigm? What are adequate notions of semantics, composition, equivalence? How can services be modeled and analyzed? This paper addresses and...

In this paper we propose a framework for SOA covering such important features as proper termination (soundness) and correct corre-lation of tasks. Within this framework, we define a method for the cal-culation of the price of services. Our framework is compositional in the sense that composing a system from subsystems that meet our correct-ness req...

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 th...

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 a...

This paper addresses the problem of analyzing the interaction between BPEL processes. We present a technology chain that starts out with a BPEL process and transforms 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 g...

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...

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 de...

We present a Petri net semantics for the Business Process Execution Language for Web Services (BPEL). Our semantics covers the standard behaviour of BPEL as well as the exceptional behaviour (e.g. faults, events, compensation). The semantics is implemented as a parser that translates BPEL specifications into the input language of the Petri net mode...

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...

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.

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...

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 specifled in BPEL can be transformed into a Petri net.

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 'GALSiftcation' of a baseband processor for WLAN. Details of th...

Based on a previously reported request driven technique for Globally-Asynchronous Locally-Synchronous (GALS) circuits this paper presents two significant enhancements. Firstly, the previously required local ring oscillators are avoided. Instead, an external clock with arbitrary phase for each GALS block is used. Details of the required wrapper circ...

this article, we discuss a possible path for gradually bridging this gap between the centralized mindset on current Web service platforms and researchers' vision of distributed, dynamic Web service composition

Based on a previously reported request driven technique for Globally-Asynchronous Locally-Synchronous (GALS) circuits this paper presents two significant enhancements. Firstly, the previously required local ring oscillators are avoided. Instead, an external clock with arbitrary phase for each GALS block is used. Details of the required wrapper circ...

this paper, we consider a Petri net semantics for BPEL. The semantics is complete(i.e., covers all the standard and exceptional behaviour of BPEL), and formal (i.e., feasiblefor model checking). With Petri nets, several elegant technologies such as the theoryof workflow nets [vdA98], a theory of controllability [Mar04, Sch04], a long list of verifi...

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