Onto.PT: Towards the Automatic Construction of a Lexical Ontology ...

140 Chapter 8. Onto.PT: a lexical ontology for Portuguese
Figure 8.4: OntoBusca, Onto.PT’s web interface.
Wordnet Association, with an Onto.PT synset.
8.3.1 Summary of evaluation so far
Among the possible strategies to evaluate an ontology, a survey by
Brank et al. (2005) presents four, which are probably the most commonly followed
when it comes to domain ontologies:
• Manual evaluation, performed by humans;
• Comparison with an existing gold standard, eventually another ontology;
• Coverage evaluation, based on a dataset on the same domain;
• Task-based evaluation, where the ontology is used by an application to achieve
some task.
Even though Onto.PT is not a domain ontology, we can say that, throughout this
research, and depending on what we were evaluating, we have followed the first, the
second and the third approaches.
First, in the extraction step (chapter 4), before performing the manual classification
of some extractions, we evaluated the coverage of the extracted information
by handcrafted thesauri, and by a newspaper corpus. Attention should be given to
the coverage evaluation because, as Onto.PT is broad-coverage, it is not possible to
find something like a corpus of its own domain. A language thesaurus is probably
the closest thing. Furthermore, the corpus was used to validate the coverage of the
relations, and was based on a limited set of discriminating patterns. When it comes
to estimating the accuracy of the extracted relations, manual evaluation is probably