Wikipedia is the biggest collaboratively created source of encyclopaedic knowledge. Growing beyond the borders of any traditional encyclopaedia, it is facing new problems of knowledge management: The current excessive usage of article lists and categories witnesses the fact that 19th century content organization technologies like inter-article references and indices are no longer su#cient for today's needs.

A common perception is that there are two competing visions for the future evolution of the Web: the Semantic Web and Web 2.0. A closer look, though, reveals that the core technologies and concerns of these two approaches are complementary and that each field can and must draw from the other’s strengths. We believe that future web applications will retain the Web 2.0 focus on community and usability, while drawing on Semantic Web infrastructure to facilitate mashup-like information sharing. However, there are several open issues that must be addressed before such applications can become commonplace. In this paper, we outline a semantic weblogs scenario that illustrates the potential for combining Web 2.0 and Semantic Web technologies, while highlighting the unresolved issues that impede its realization. Nevertheless, we believe that the scenario can be realized in the short-term. We point to recent progress made in resolving each of the issues as well as future research directions for each of the communities.

Abstract. In this article, we propose a new ontology evolution approach that combines a top-down and a bottom-up approach. This means that the manual request for changes (top-down) by the ontology engineer is complemented with an automatic change detection mechanism (bottom-up). The approach is based on keeping track of the different versions of ontology concepts throughout their lifetime (called virtual versions). In this way, changes can be defined in terms of these virtual versions. 1

Abstract. Knowledge management solutions relying on central repositories sometimes have not met expectations, since users often create knowledge adhoc using their individual vocabulary and using their own decentral IT infrastructure (e.g., their laptop). To improve knowledge management for such decentralized and individualized knowledge work, it is necessary to, first, provide a corresponding IT infrastructure and to, second, deal with the harmonization of different vocabularies/ontologies. In this paper, we briefly sketch the technical peer-to-peer platform that we have built, but then we focus on the harmonization of the participating ontologies. Thereby, the objective of this harmonization is to avoid the worst incongruencies by having users share a core ontology that they can expand for local use at their will and individual needs. The task that then needs to be solved is one of distributed, loosely-controlled and evolving engineering of ontologies. We have performed along these lines. To support the ontology engineering process in the case study we have furthermore extended the existing ontology engineering environment, OntoEdit. The case study process and the extended tool are presented in this paper. 1

Robust and scalable user context management is the key enabler for the emerging context- and situation-aware applications, and ontology-based approaches have shown their usefulness for capturing especially context information on a high level of abstraction. But so far the problem has not been approached as a data management problem, which is key to scalability and robustness. The specific challenges lie in the imperfection of high-level context information, its time-dependence and the variability in the dynamics between its different elements.

Topics in education are changing with an ever faster pace. ELearning resources tend to be more and more decentralized. Users increasingly need to be able to use the resources of the web. For this, they should have tools for finding and organizing information in a decentralized way. In this paper, we show how an ontologybased tool suite allows to make the most of the resources available on the web.

The main goal of this paper is to propose a distributed paradigm for reasoning with multiple ontologies connected by semantic mappings. The contribution of the paper to this goal is twofold. From the theoretical point of view we characterize the problem of global subsumption (i.e. the problem of subsumption in a set of local ontologies connected by semantic mappings) as a suitable fixpoint combination of operators that compute subsumptions in the local ontologies. This allows us to define a sound and complete algorithm for global subsumptions which calls black-boxes sub-routines for local subsumptions. The second contribution is the description of a prototype implementation of such algorithm in a peer-to-peer architecture.

Abstract. Existing mature ontology engineering approaches are based on some basic assumptions that are often violated in practice, in particular in the Semantic Web. Ontologies often need to be built in a decentralized way, ontologies must be given to a community in a way such that individuals have partial autonomy over them and ontologies have a life cycle that involves an iteration back and forth between construction/modification and use. While recently there have been some initial proposals to consider these issues, they lack the appropriate rigor of mature approaches. i.e. these recent proposals lack the appropriate depth of methodological description, which makes the methodology usable, and they lack a proof of concept by a long-lived case study. In this paper, we revisit mature and new ontology engineering methodologies. We provide an elaborate methodology that takes decentralization, partial autonomy and iteration into account and we demonstrate its proof-of-concept in a real-world cross-organizational case study. 1

Abstract. Ontologies play a key role in the realization of the Semantic Web. An ontology is used as an explicit specification of a shared conceptualization of a given domain. When such a domain evolves, the describing ontology needs to evolve too. In this paper, we present an approach that allows tracing evolution on the instance level. We use event types as an abstraction mechanism to define the semantics of changes. Furthermore, we introduce a new event-based approach to keep depending artifacts consistent with a changing instance base. 1

Abstract: The wealth and diversity of information available in the internet or local hyper-media corpora has increased while our ability to search and retrieve relevant information is being reduced. Searching in distributed hypermedia has received increased attention by the scientific community in the past few years where integration solutions which rely on semantics are considered as efficient. In this paper we propose a new scheme for integrated searching in distributed hypermedia sources using a multi-layer ontology. Searching tasks are carried out in the metadata level, where information concerning hypermedia objects is published, managed and stored in the form of a scalable description of knowledge domains