A.H.M. ter Hofstede

Workflow Patterns

Differences in features supported by the various contemporary commercial workflow management systems point to different insights of suitability and different levels of expressive power. The challenge, which we undertake in this paper, is to systematically address workflow requirements, from basic to complex. Many of the more complex requirements identified, recur quite frequently in the analysis phases of workflow projects, however their implementation is uncertain in current products. Requirements for workflow languages are indicated through workflow patterns. In this context, patterns address business requirements in an imperative workflow style expression, but are removed from specific workflow languages. The paper describes a number of workflow patterns addressing what we believe identify comprehensive workflow functionality. These patterns provide the basis for an in-depth comparison of a number of commercially availablework flow management systems. As such, this paper can be seen as the academic response to evaluations made by prestigious consulting companies. Typically, these evaluations hardly consider the workflow modeling language and routing capabilities, and focus more on the purely technical and commercial aspects.

From BPMN Process Models to BPEL Web Services

The business process modelling notation (BPMN) is a graph-oriented language in which control and action nodes can be connected almost arbitrarily. It is supported by various modelling tools but so far no systems can directly execute BPMN models. The business process execution language for Web services (BPEL) on the other hand is a mainly block-structured language supported by several execution platforms. In the current setting, mapping BPMN models to BPEL code is a necessary step towards unified and standards-based business process development environments. It turns out that this mapping is challenging from a scientific viewpoint as BPMN and BPEL represent two fundamentally different classes of languages. Existing methods for mapping BPMN to BPEL impose limitations on the structure of the source model. This paper proposes a technique that overcomes these limitations. Beyond its direct relevance in the context of BPMN and BPEL, this technique addresses difficult problems that arise generally when translating between flow-based languages with parallelism

Achieving a general, formal and decidable approach to the OR-Join in workflow using reset nets

Workflow languages offer constructs for coordinating tasks. Among these constructs are various types of splits and joins. One type of join, which shows up in various incarnations, is the OR-join. Different approaches assign a different (often only intuitive) semantics to this type of join, though they do share the common theme that synchronisation is only to be performed for active threads. Depending on context assumptions this behaviour may be relatively easy to deal with, though in general its semantics is complicated, both from a definition point of view (in terms of formally capturing a desired intuitive semantics) and from a computational point of view (how does one determine whether an OR-join is enabled?). In this paper the concept of OR-join is examined in detail in the context of the workflow language YAWL, a powerful workflow language designed to support a collection of workflow patterns and inspired by Petri nets. The OR-joins definition is adapted from an earlier proposal and an algorithmic approach towards determining OR-join enablement is examined. This approach exploits a link that is proposed between YAWL and Reset nets, a variant of Petri nets with a special type of arc that can remove all tokens from a place.

How to Formalize It? Formalization Principles for Information System Development Methods

Although the need for formalisation of modelling techniques is generally recognised, not much literature is devoted to the actual process involved. This is comparable to the situation in mathematics where focus is on proofs but not on the process of proving. This paper tries to accomodate for this lacuna and provides essential principles for the process of formalisation in the context of modelling techniques as well as a number of small but realistic formalisation case studies.

Bridging Global and Local Models of Service-Oriented Systems

A service-oriented system is a collection of independent services that interact with one another through message exchanges. Languages such as the Web Services Description Language (WSDL) and the Business Process Execution Language (BPEL) allow developers to capture the interactions in which an individual service can engage, both from a structural and from a behavioral perspective. However, in large service-oriented systems, stakeholders may require a global picture of the way services interact with each other, rather than multiple small pictures focusing on individual services. Such global models are especially useful when a set of services interact in such a way that none of them sees all messages being exchanged, yet interactions between some services may affect the way other services interact. Unfortunately, global models of service interactions may sometimes capture behavioral constraints that cannot be enforced locally. In other words, some global models may not be translatable into a set of local models such that the sum of the local models equals the original global model. Starting from a previously proposed language for global modeling of service interactions, this paper defines an algorithm for determining if a global model is locally enforceable and an algorithm for generating local models from global ones. It also shows how local models are mapped into templates of BPEL process definitions.

Towards the construction of workflow-suitable conceptual modelling techniques

Despite their high‐level and graphical nature, workflow specifications require a significant amount of implementation detail — for example application programming interface, database access and programming mechanisms for information flow — for a more comprehensive validation than is currently possible. This is currently recognized as a deficiency in workflow conceptualization. Although conceptual modelling techniques are available which are expressive, comprehensive and precise enough, we believe, their concepts and features are not specialized enough for workflow domains. In this paper, we offer a comparative insight into techniques which characterize different aspects and approaches of workflow specifications. These are: structured process modelling, object‐oriented modelling, behavioural process modelling and business‐oriented modelling. In particular, we determine gaps for workflows capturing operational business transaction processing, for example those of insurance claims, bank loans and government‐related registration. For technique construction, we describe five workflow suitability principles.

Workflow patterns put into context

In his paper “Approaches to Modeling Business Processes. A Critical Analysis of BPMN, Workflow Patterns and YAWL”, Egon Börger criticizes the work of the Workflow Patterns Initiative in a rather provocative manner. Although the workflow patterns and YAWL are well established and frequently used, Börger seems to misunderstand the goals and contributions of the Workflow Patterns Initiative. Therefore, we put the workflow patterns and YAWL in their historic context. Moreover, we address some of the criticism of Börger by pointing out the real purpose of the workflow patterns and their relationship to formal languages (Petri nets) and real-life WFM/BPM systems.

Event log imperfection patterns for process mining

Process-oriented data mining (process mining) uses algorithms and data (in the form of event logs) to construct models that aim to provide insights into organisational processes. The quality of the data (both form and content) presented to the modeling algorithms is critical to the success of the process mining exercise. Cleaning event logs to address quality issues prior to conducting a process mining analysis is a necessary, but generally tedious and ad hoc task. In this paper we describe a set of data quality issues, distilled from our experiences in conducting process mining analyses, commonly found in process mining event logs or encountered while preparing event logs from raw data sources. We show that patterns are used in a variety of domains as a means for describing commonly encountered problems and solutions. The main contributions of this article are in showing that a patterns-based approach is applicable to documenting commonly encountered event log quality issues, the formulation of a set of components for describing event log quality issues as patterns, and the description of a collection of 11 event log imperfection patterns distilled from our experiences in preparing event logs. We postulate that a systematic approach to using such a pattern repository to identify and repair event log quality issues benefits both the process of preparing an event log and the quality of the resulting event log. The relevance of the pattern-based approach is illustrated via application of the patterns in a case study and through an evaluation by researchers and practitioners in the field.

Applications of a categorical framework for conceptual data modeling

Abstract. For successful information systems development, conceptual data modeling is essential. Nowadays a plethora of techniques for conceptual data modeling exist. Many of these techniques lack a formal foundation and a lot of theory, e.g. concerning updates or schema transformations, is highly data model specific. As such there is a need for a unifying formal framework providing a sufficiently high level of abstraction. In this paper, focus is on the applications of such a framework defined in category theory. Well-known conceptual data modeling concepts, such as relationship types, generalization, specialization, and collection types are defined from a categorical point of view in this framework and an essential advantage is its “configurable semantics”. Features such as null values, uncertainty, and temporal behavior can be added by selecting appropriate instance categories. The addition of these features usually requires a complete redesign of the formalization in traditional set-based approaches to semantics. Applications of the framework in the context of schema transformations and improved automated modeling support are discussed.

Formal description of temporal knowledge in case reports

Abstract Patient case analysis is an elementary and crucial process which clinicians are daily confronted with. The importance and complexity is reflected in the need to discuss cases in clinicopathological conferences and the documentation of more than 70 000 patient cases in MEDLINE. This paper introduces a generic patient case report language (PCRL) based on general medical temporal concepts to formalise temporal knowledge as present in case descriptions. The lack of such a generic technique is reflected by the fact that computers are very restrictive in accepting patient specific temporal information. Acceptance is almost always controlled and guided by specific predefined disease or treatment models. We strive for a case library consisting of unambiguous patient case descriptions formulated independent from future use.