Werner Retschitzegger

Context-awareness on mobile devices - the hydrogen approach

Information about the users environment offers new opportunities and exposes new challenges in terms of time-aware, location-aware, device-aware and personalized applications. Such applications constantly need to monitor the environment - called context - to allow the application to react accordingly to this context. Context-awareness is especially interesting in mobile scenarios where the context of the application is highly dynamic and allows the application to deal with the constraints of mobile devices in terms of presentation and interaction abilities and communication restrictions. Current context-aware applications often realize sensing of context information in an ad hoc manner. The application programmer needs to deal with the supply of the context information including the sensing of the environment, its interpretation and its disposal for further processing in addition to the primary purpose of the application. The close interweavement of device specific context handling with the application obstructs its reuse with other hardware configurations. Recently, architectures providing support for context-aware applications have been developed. Up to now such architectures are not trimmed to the special requirements of mobile devices regarding particularly the limitations of network connections, limited computing power and the characteristics of mobile users. This paper proposes an architecture and a software framework - the hydrogen context framework -which support context-awareness for considering these constraints. It is extensible to consider all kind of context information and comprises a layered architecture. To prove the feasibility the framework has been implemented to run on mobile devices. A context-aware postbox is realized to demonstrate the capabilities of the framework.

Lifting metamodels to ontologies: a step to the semantic integration of modeling languages

The use of different modeling languages in software development makes their integration a must. Most existing integration approaches are metamodel-based with these metamodels representing both an abstract syntax of the corresponding modeling language and also a data structure for storing models. This implementation specific focus, however, does not make explicit certain language concepts, which can complicate integration tasks. Hence, we propose a process which semi-automatically lifts metamodels into ontologies by making implicit concepts in the metamodel explicit in the ontology. Thus, a shift of focus from the implementation of a certain modeling language towards the explicit reification of the concepts covered by this language is made. This allows matching on a solely conceptual level, which helps to achieve better results in terms of mappings that can in turn be a basis for deriving implementation specific transformation code.

A framework for workflow management systems based on objects, rules and roles

The goal of this paper is to present an approach for the development of workflow management systems supporting both reusability and adaptability, i.e., customization due to frequently changing requirements in an organization. The principal contribution is the introduction of an object-oriented application framework for constructing such workflow management systems balancing between reusability and adaptability. The underlying techniques are an object-oriented workflow model, object evolution via an integrated role model, and the support of business policies via an integrated rule model.

Editorial: BeAware!-Situation awareness, the ontology-driven way

Information overload is a severe problem for human operators of large-scale control systems as, for example, encountered in the domain of road traffic management. Operators of such systems are at risk to lack situation awareness, because existing systems focus on the mere presentation of the available information on graphical user interfaces-thus endangering the timely and correct identification, resolution, and prevention of critical situations. In recent years, ontology-based approaches to situation awareness featuring a semantically richer knowledge model have emerged. However, current approaches are either highly domain-specific or have, in case they are domain-independent, shortcomings regarding their reusability. In this paper, we present our experience gained from the development of BeAware!, a framework for ontology-driven information systems aiming at increasing an operators situation awareness. In contrast to existing domain-independent approaches, BeAware!s ontology introduces the concept of spatio-temporal primitive relations between observed real-world objects thereby improving the reusability of the framework. To show its applicability, a prototype of BeAware! has been implemented in the domain of road traffic management. An overview of this prototype and lessons learned for the development of ontology-driven information systems complete our contribution.

Coordination in Workflow Management Systems - A Rule-Based Approach

Coordination is a key requirement of software systems where different parts have to be adjusted in order to reach a common goal. A prominent example thereof are workflow management systems (WFMS). They in particular require flexible mechanisms to realize different kinds of coordination, which are called coordination policies. This need for flexibility emerges from the fact that coordination policies in WFMS are subject to frequent changes caused by the business environment. Flexibility is required in different directions, ranging from a dynamic evolution of existing policies to proper reactions to unpredictable situations. Active object-oriented database systems (AOODBS) along with their basic mechanism in terms of Event/Condition/Action (ECA) rules seem to be a promising technology in order to cope with these requirements. ECA rules allow for an event-driven realization of context- and time-dependent behavior which constitutes a major property of coordination policies. By encapsulating coordination policies within ECA rules, general knowledge can be represented independently from specific business processes. This both eases modification of coordination policies and enhances their reusability. To demonstrate the power of this approach, the paper identifies various coordination policies required within different areas of WFMS and outlines their mapping to ECA rules.

Automated verification of model transformations based on visual contracts

Model-Driven Engineering promotes the use of models to conduct the different phases of the software development. In this way, models are transformed between different languages and notations until code is generated for the final application. Hence, the construction of correct Model-to-Model (M2M) transformations becomes a crucial aspect in this approach.Even though many languages and tools have been proposed to build and execute M2M transformations, there is scarce support to specify correctness requirements for such transformations in an implementation-independent way, i.e., irrespective of the actual transformation language used.In this paper we fill this gap by proposing a declarative language for the specification of visual contracts, enabling the verification of transformations defined with any transformation language. The verification is performed by compiling the contracts into QVT to detect disconformities of transformation results with respect to the contracts. As a proof of concept, we also report on a graphical modeling environment for the specification of contracts, and on its use for the verification of transformations in several case studies.

X-ray: towards integrating XML and relational database systems

Relational databases get more and more employed in order to store the content of a web site. At the same time, XML is fast emerging as the dominant standard at the hypertext level of web site management describing pages and links between them. Thus, the integration of XML with relational database systems to enable the storage, retrieval and update of XML documents is of major importance. This paper presents X-Ray, a generic approach for integrating XML with relational database systems. The key idea is that mappings may be defined between XML DTDs and relational schemata while preserving their autonomy. This is made possible by introducing a meta schema and meta knowledge for resolving data model heterogeneity and schema heterogeneity. Since the mapping knowledge is not hard-coded but rather reified within the meta schema, maintainability and changeability is enhanced. The meta schema provides the basis for X-Ray to automatically compose XML documents out of the relational database when requested and decompose them when they have to be stored.

Customisation for ubiquitous web applications: a comparison of approaches

Ubiquitous web applications adhering to the anytime/anywhere/anymedia paradigm are required to be customisable meaning the adaptation of their services towards a certain context. Several approaches for customising ubiquitous Web applications have been already proposed, each of them having different origins and pursuing different goals for dealing with the unique characteristics of ubiquity. This paper compares some of these proposals, trying to identify their strengths and shortcomings. As a prerequisite, an evaluation framework is suggested which categorises the major characteristics of customisation into different dimensions. On the basis of this framework, customisation approaches are surveyed and compared to each other, pointing the way to next-generation customisation approaches.

An Example Is Worth a Thousand Words: Composite Operation Modeling By-Example

Predefined composite operations are handy for efficient modeling, e.g., for the automatic execution of refactorings, and for the introduction of patterns in existing models. Some modeling environments provide an initial set of basic refactoring operations, but hardly offer any extension points for the user. Even if extension points exist, the introduction of new composite operations requires programming skills and deep knowledge of the respective metamodel. In this paper, we introduce a method for specifying composite operations within the users modeling language and environment of choice. The user models the composite operation by-example, which enables the semi-automatic derivation of a generic composite operation specification. This specification may be used in various modeling scenarios, like model refactoring and model versioning. We implemented the approach in the Operation Recorder and performed an evaluation by defining multiple complex refactorings for UML diagrams.

Model transformation by-example: a survey of the first wave

Model-Driven Engineering (MDE) places models as first-class artifacts throughout the software lifecycle. In this context, model transformations are crucial for the success of MDE, being comparable in role and importance to compilers for high-level programming languages. Thus, several model transformation approaches have been developed in the last decade, whereby originally most of them are based on the abstract syntax of modeling languages. However, this implementation specific focus makes it difficult for modelers to develop model transformations, because they are familiar with the concrete syntax but not with its computer internal representation. To tackle this problem, model transformation by-example approaches have been proposed which follow the same fundamental idea as query by-example and programming by-example approaches. Instead of using the computer internal representation of models, examples represented in concrete syntax are used to define transformations. Because different transformation scenarios occur in MDE, different by-example approaches have been developed. This chapter gives an overview on the emerging concepts, techniques, and approaches in this young by-example area.