ABSTRACT
There is no shortage of potential future use case scenarios for Semantic Web technologies, ranging from information integration over ambient intelligence to expert systems. Such scenarios are reported in the proceedings of various research and industrial conferences, edited research books, and project reports, and we give corresponding pointers in Section 9.10. These reports are a clear indication of the current state of the art, namely, that Semantic Web technologies are currently in a transition phase from research into applications. This is also witnessed by the industrial development of ontology editors and reasoners, as presented in Section 8.5. Rather than providing yet another compilation of potential use cases, in this
chapter we focus instead on a selected few real life applications, i.e. applications which are really being used. They show the uptake of Semantic Web technologies in practice, and witness the currently ongoing transition from research into applications. Our selection is necessarily subjective; however, we are confident that we have captured some of the most relevant applications to date. But before we actually come to the applications, let us dwell for a moment
on the question what – and what not – applications of Semantic Web technologies actually are. It turns out that it is not easy to give such a definition. Naively speaking, something is an application of Semantic Web technolo-
gies if it actually uses Semantic Web technologies. But this leaves us with the question what Semantic Web technologies are. And in attempting to define this term, we have to realize that Semantic Web technologies, generally speaking, are rather a vaguely defined class of technologies than a concrete technology – vaguely defined as having something to do with metadata, data exchange and integration, knowledge representation, the Web, ontologies, and following the general visions explained in Chapter 1, but not defined in any crisp way. Perhaps Semantic Web technologies are still too young for such a crisp definition. But let’s try anyway. A workable and straightforward definition of applications of Semantic Web
technologies is that they are applications which use any of the standardized ontology languages, i.e. RDF or OWL. This might probably be a safe definition considering the fact that we have these languages available. However, it leaves out applications using RIF (which at the time of this writing is in the last stages of becoming a W3C recommendation, but isn’t one yet). Likewise,
before OWL was there,1 or ontology languages which are not standardized but appear to be viable alternatives?2 The definition would miss these. And at the same time it would include uses of RDF which are, probably, not at all in the spirit of the Semantic Web. So let us attempt a much more general definition and say that applications
of Semantic Web technologies are defined by using metadata in a metadataspecific way. This sounds about right, but if you think about it for a while then you may start to wonder about the precise definition of metadata and of metadata-specific. In some sense, metadata is simply data describing other data – but again this definition is not entirely crisp. None of the suggestions above is a satisfactory definition, and indeed, we
think it is futile to dwell on this point longer at this stage. Future developments will clarify matters.3
