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

62 Chapter 4. Acquisition of Semantic Relations
suggestions in Simões et al. (2010). However, in order to minimise the probability
of generating invalid lemmas, if they do not exist in TeP nor PAPEL, the tb-triple
is discarded.
For handling the wikitext of the Wiktionary.PT dump, we developed a specific
parser (Anton Pérez et al., 2011). Although there is an available API, JWKTL 12 , for
processing Wiktionary (Zesch et al., 2008a), it is only compatible with the English
and German versions of the resource. The main problem is that different language
editions of Wiktionary use distinct delimiter elements to represent the information
of each entry, so every Wiktionary parser needs to be adapted according to the
language edition. Since the source code of JWKTL was not available, we could not
adapt it for Wiktionary.PT.
In the dictionary conversion process, only definitions of open-category words
were used, and changed to one common notation: nome for nouns, verbo for verbs,
adj for adjectives and adv for adverbs. The format adopted for representing the
dictionaries contains a definition per line. Before the definition, we include the
definiendum and its POS, as in the following definition for the word coco (coconut):
coco nome fruto gerado pelo coqueiro, muito usado para se fazer
doces e para consumo de seu líquido
In this format, words with more than one definition originate more than one
line. Also, since Wiktionary provides synonymy lists for some of its entries, we
transformed these lists in definitions with only one word, as in the following example
for the synonyms of the word bravo (brave):
Sinónimos: corajoso, destemido ⇒
bravo adj corajoso
bravo adj destemido
After the conversion of DA and Wiktionary.PT we obtained about 229,000 and
72,000 definitions, respectively for each dictionary. We do not have direct access to
DLP, but we can say that it contains 176,000 definitions which gave origin to, at
least, one relation.
Wiktionary.PT is the smaller resource, which resulted in the lowest number of
definitions among the three dictionaries. However, before collecting these definitions,
we discarded: (i) definitions corresponding to words in other languages; (ii) definitions
of closed-category and inflected words (including verbal forms); (iii) definitions
in entries with alternative syntaxes, not recognised by our parser. As Wiktionaries
are created by volunteers, often not experts, and because there is no standard syntax
for representing Wiktionary entries in wikitext, the structure of the entries is fairly
inconsistent. It is thus impossible to develop a parser to handle all syntax variations,
and thus 100% reliable. This problem seems to be common to other editions
of Wiktionary, as it is referred by other authors (e.g. Navarro et al. (2009)).
4.2.3 Regularities in the Definitions
One of the main reasons for using dictionaries in the automatic acquisition of lexicalsemantic
relations is that they typically use simple and systematic vocabulary, suitable
for being exploited in information extraction. Having this in mind, during the
creation of PAPEL, we developed a set of grammars, with lexical-syntactic patterns
12 See http://www.ukp.tu-darmstadt.de/software/jwktl/ (September 2012)