Semantic Web-Based Information Systems: State-of-the-Art ...

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Figure 9. An Edutella query expressed in simplified RDF. It is directed toward the
(machine) Semantic Web and not very understandable for humans.
Edutella builds upon metadata standards defined for the World Wide Web (WWW)
and provides an RDF-based metadata infrastructure for P2P applications, building
on the JXTA framework (JXTA, n.d.).
To show the kind of queries that Edutella can manage, consider the query depicted
in Figure 9 (as a simplified RDF graph). X represents the resource we are looking
for, and the arcs are properties of that resource. In plain English, the query asks for
the following (in counter-clockwise order):
All scientific works on the subject of politics, having Lebanon as subject or keyword,
with a title (Y) written in English, German, or French, created or contributed to by
a person (Z), employed at a university, and created after 1980. 21
Edutella takes queries of the previous complexity, distributes them to peers that
have declared themselves capable of answering this type of query, collects the
answers, and returns them to the originator. It is possible that parts of the answers
are located on different peers. In the example, the university employee information
is perhaps not located on the same server as the resource metadata, but Edutella is
able to handle these kinds of situations in a transparent manner (Nilsson, Naeve,
& Palmér, 2004).
Although the Edutella query depicted in Figure 9 is logically precise and easy for
machines to process, it is not very understandable for humans. When the queries
are formulated by humans, as opposed to agents, for example, there is a need to
represent them in a more humanly understandable form. Figure 10 shows the same
Edutella query presented on the human Semantic Web through a query interface in
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