2.2 Extraction Information from the Web using Patterns
25
ulation.
2.2.2 Sketch of the Approach
In this section, we present a global approach to populate an initial ontology
O.
As discussed earlier in this chapter, we are confronted with the design constraint
that the availability of the search engines is limited. This enforces us to formulate
precise queries, in order to obtain highly relevant search results.
Now, if an ontology with complete classes is given, the task is to only populate
the relations, i.e. to find relation instances. In other words, we have to find and
recognize natural language formulations of the
subject – relation – object triplets.
If we are interested in the class instantiation problem, the tasks are quite similar.
For a class named
n, the task is to find terms
t where the triplet
t
is a
n is expressed.
Hence, the class instantiation problem can easily be rewritten into a relation instan-
tiation problem for incomplete classes.Suppose we are handed the following class
instantiation problem:
O = (
{c
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