Juergen Mangler

Web services for blended learning patterns

Web services currently draw the attention of learning technology researchers and practitioners to leverage the degree of interoperability and extensibility of current and future learning platform solutions. One very recent research thread in blended learning concentrates on capturing Web-based learning processes and their subsequent instantiation on learning technology in the form of reusable patterns. This paper presents CEWebS, an open Web-service-based learning technology architecture designed for supporting the implementation of these patterns with conceptual guidance by the layered blended learning systems structure (BLESS) model.

Definition and enactment of instance-spanning process constraints

Currently, many approaches address the enforcement and monitoring of constraints over business processes. However, main focus has been put on constraint verification for intra-instance process constraints so far, i.e., constraints that affect single instances. Existing approaches addressing instance-spanning constraints only consider certain scenarios. In other words, a holistic approach considering intra-instance, inter-instance, and inter-process constraints is still missing. This paper aims at closing this gap. First of all, we show how the Identification and Unification of Process Constraints (IUPC) compliance framework enables the definition of instance-spanning process constraints in a flexible and generic way. Their enactment and enforcement is demonstrated within a prototypical implementation based on a service-oriented architecture.

A structured marketplace for arbitrary services

Creating simple marketplaces with common rules, that enable the dynamic selection and consumption of functionality, is the missing link to allow small businesses to enter the cloud, not only as consumers, but also as vendors. In this paper, we present the concepts behind a hybrid service and process repository that can act as the foundation for such a marketplace, as well as a prototype that allowed us to test various real-world scenarios. The advantage of a hybrid service and process repository is that, it not only holds a flat list of services, but also exposes a generic set of use cases, that it obtains information on how specific services can be used to implement the use cases as well as information to select services at run-time according to customers goal functions.

AW-RBAC: Access Control in Adaptive Workflow Systems

Flexibility is one of the key challenges for Workflow Systems nowadays. Typically, a workflow covers the following four aspects which might all be subject to change: control flow, data flow, organizational structures, and application components (services). Existing work in research and practice shows that changes must be applied in a controlled manner in order to avoid security problems. In this context, attempts have been made to manage administrative or operative changes using role-based access control (RBAC) models. However, most approaches focus on either administrative changes such as role updating and administration or operative changes, for example, inserting a new activity into a running workflow instance. The distinct handling of certain changes is cumbersome and hence should be reduced by introducing a RBAC model that pays attention to all kinds of possible workflow changes. Hence, in this paper, we present an extended RBAC model for adaptive workflow systems (AW-RBAC) that includes change operations and a variety of objects that are subject to change within workflow systems. Under such a model supervised administrative and operative changes can be enforced on a set of objects in workflow systems. Doing so, the AW-RBAC model improves security during workflow changes and reduces administration costs. The AW-RBAC model is evaluated by means of practical examples and a proof-of-concept implementation.

On the Origin of Services Using RIDDL for Description, Evolution and Composition of RESTful Services

WSDL as a description language serves as the foundation for a host of technologies ranging from semantic annotation to composition and evolution. Although WSDL is well understood and in widespread use, it has its shortcomings which are partly imposed by the way how the SOAP protocol works and is used. Cloud computing fostered the rise of Representational State Transfer (REST), a return to arguably simpler but more flexible ways to expose services solely through the HTTP protocol. For RESTful services many achievements that have been acquired have to be rethought and reapplied. We perceive that one of the biggest hurdles is the lack of a dedicated and simple yet powerful language to describe RESTful services. In this paper we want to introduce RIDDL, a flexible and extensible XML based language that not only allows to describe services but also covers the basic requirements of service composition and evolution to provide a clean foundation for further developments.

Quo vadis interface definition languages? Towards a interface definition language for RESTful services

Current web-service description languages like WSDL are very powerful and many topics, like how to describe the composition of web-services, have received much attention by the scientific community. With the rise of RESTful webservices, resources come to the focus of service developers, with the need to transfer many well understood problems to a new paradigm. RESTful services up to now are most commonly described in a natural language, and there is no good interface description language, as WSDL (2.0) is clumsy to use and WADL lacks features and widespread use. In this paper we want to analyze common interface description languages, their properties and shortcomings and we introduce RIDDL, a flexible and extensible service description language to cover description and composition.

Classification and Formalization of Instance-Spanning Constraints in Process-Driven Applications

In process-driven applications, typically, instances share human, computer, and physical resources and hence cannot be executed independently of each other. This necessitates the definition, verification, and enforcement of restrictions and conditions across multiple instances by so called instance-spanning constraints (ISC). ISC might refer to instances of one or several process types or variants. While real-world applications from, e.g., the logistics, manufacturing, and energy domain crave for the support of ISC, only partial solutions can be found. This work provides a systematic ISC classification and formalization that enables the verification of ISC during design and runtime. Based on a collection of 114 ISC from different domains and sources the relevance and feasibility of the presented concepts is shown.

Using Stateful Activities to Facilitate Monitoring and Repair in Workflow Choreographies

The repair of faulty processes (workflows, web service compositions) needs information about the state of the involved web services. We introduce an architecture where (web service based) activities and their instances are treated as manageable resources. Based on the WAMO Model our activities provide detailed information about the state they currently hold, possible states they can reach, as well as operations to affect the current state. The strength of this approach is that we can introduce independent repair and monitoring facilities, that utilize a generic way to access information about running activities.

Developing Cooperative Environment Web Services Based on Action Research

Current technology has disappointed many users of cooperative learning environments by its complexity and only slow and tough adaptability to specific users’ requirements. In order to compensate for these deficiencies, we use Action Research to guide us in a process in which we co-develop and improve open source, Web service based modules that directly and intuitively support learning, cooperation, and facilitation processes based on users’ experiences. In this paper we characterize selected services, sketch our environment and propose an accompanying research procedure that allows us to assess and cyclically improve and extend our tools to closely match both their underlying didactics and users’ needs.

Rule-Based Runtime Monitoring of Instance-Spanning Constraints in Process-Aware Information Systems

Instance-spanning constraints (ISC) constitute a crucial instrument to establish coordination between multiple instances in Process-Aware Information Systems. ISC need to be verified and monitored at design as well as runtime. In this work we propose a rule-based approach for runtime monitoring of ISC. We base our work on the well known Rete algorithm and research ways structure the network in such a way that improves matching speed for ISC. We show through a technical evaluation that (1) a rule-based approach is feasible for performing runtime monitoring of ISC and (2) that the heuristics we extract for structuring the Rete network improve the rule matching speed.