This thesis is driven by the motivation to explore a way of working collaboratively that closely reflects the World Wide Web (WWW), more specifically the potential of the Web architecture built on Semantic Web technologies and Linked Data. The goal is to describe a generic approach and architecture that satisfies the needs for loose collaboration and collective knowledge construction as exemplified by the applications described in this thesis. This thesis focuses on a contribution-centric architecture which allows for flexible applications that support loose forms of collaboration. The first research question deals with how Web-based collective knowledge construction can be supported. The second research question explores the characteristics of collective knowledge construction with respect to the Open World Assumption (OWA). The OWA implies that complete knowledge about a subject cannot be assumed at any time, which is one of the most fundamental properties of the WWW. The third research question investigates how Semantic Web technologies be used in order to support such a contribution-centric architecture. The thesis and its underlying publications are of a technical character and are always grounded in theoretical models and considerations that have led to functional implementations. The research has evolved in iterative development processes and was explicitly directed at building applications that can be used in collaborative settings and that are based on standardized Web technologies. One of the main outcomes, an information model, was developed together with such an application and provides a number of novel approaches in the context in which it was designed. The validity of the presented research is supported by evaluations from different perspectives: a list of implemented applications and showcases, results from structured interviews that have investigated the suitability for various resource annotation processes, as well as scalability aspects. The thesis concludes that it is ultimately up to the application how "loose" the collaboration should be and to which extent the OWA is incorporated. The presented architecture provides a toolkit to support the development of loosely collaborative applications. The showcased applications allow the construction of collaborative conceptual models and to collaboratively annotate educational resources. They show the potential of the used technology stack and the introduced contribution-centric architecture that sits on top if it. / <p>QC 20140417</p>

In Ontology-Based Data Access (OBDA), user queries are evaluated over a set of facts under the open world assumption, while taking into account background knowledge given in the form of a Description Logic (DL) ontology. Motivated by situation awareness applications, temporal conjunctive queries (TCQs) have recently been proposed as a useful extension of traditional OBDA to support the processing of temporal information. This paper extends the existing complexity analysis of TCQ entailment to very expressive DLs underlying the OWL 2 standard, and in contrast to previous work also allows for queries containing transitive roles. / This is an extended version of the paper “Temporal Conjunctive Queries in Expressive Description Logics with Transitive Roles”, published in the Proceedings of the 28th Australasian Joint Conference on Artificial Intelligence (AI’15).