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WORKSHOP
Thesauri
thesauri are controlled vocabularies with a hierarchical structure. In this
respect, they reuse the same approach as the classiication methodologies, but
on the level of the components of natural speech. the main items which are
registered in a thesaurus are generally called descriptors, as they are used to
describe the contents of a textual object. the entries in the thesaurus are reined
by a sophisticated system of links to broader terms, narrower terms,
synonyms and related terms.
the advantage of the use of thesauri is that research can automatically be:
• redirected from registered synonyms to the corresponding descriptors;
• limited to narrower terms if the number of results exceeds a certain threshold;
• extended to broader and/or related terms if the results are too poor.
Although a big step forwards, thesauri also have their shortcomings.
the quality of the research results depends on the quality of the use of the
descriptors. furthermore, only the main concepts of a text will be taken
into consideration. So there is always the risk that texts are only retrieved
in the context they are prepared for, while other present concepts are not
found.
Semantic networks
the idea of thesauri is driven forward by the technologies in the context
of a semantic network. they are mainly based on the use of ontologies, which
are comparable to thesauri, but instead of linking terms, they describe the relations
of concepts. the example overleaf illustrates this approach in comparison
with thesauri.
the example is simpliied, but it is obvious that the description of the nature
of the relation is much more useful than a pure link.
the evaluation of these descriptions allows for some logical conclusions
which can automatically be made on such basis. In semantic networks, heritage
is an important aspect. So, on a deeper level, the properties of the hyperonymic
level are inherited and are also available for association with other
concepts.
As the work for the creation and maintenance of thesauri is already very
time-consuming and complex, the elaboration of ontologies is even more
complicated. this is why this technology is not yet used for big projects or
large amounts of data, but for small excerpts. the spanning of the Internet by
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