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

3.1. Lexical Knowledge Bases 35
OpenThesaurus.PT 13 (hereafter, OT.PT) is the Portuguese version of a collaborative
thesaurus initiative (Naber, 2004). It is approximately four times smaller
than TeP. OT.PT contains 13,258 lexical items, organised in 4,102 synsets, but the
project has not had any significant development since 2006. This resource is mainly
used in the OpenOffice 14 word processor for suggesting synonyms.
Electronic dictionaries
There are several Portuguese dictionaries available for online queries, however, we
would like to mention two of them which, besides containing some additional explicit
semantic markups, are public domain and thus freely available for download and use.
Wiktionary.PT 15 is a collaborative dictionary by the Wikimedia foundation
where, besides the typical dictionary information, it is possible to add information
on semantic relations for each entry. For Portuguese however, this resource is
still small and, besides other problems, most entries do not have information about
semantic relations. On May 2012, Wiktionary.PT contained almost 180,000 entries.
However, as all Wiktionaries are multilingual, not all of those entries correspond to
Portuguese words.
Dicionário Aberto (hereafter DA, Simões and Farinha (2011); Simões et al.
(2012)) is the electronic version of an old Portuguese dictionary from 1913, maintained
by Alberto Simões in University of Minho. DA, whose orthography is currently
being modernised, has 128,521 entries. Recently, some semantic relations,
extracted using simple patterns, were added to the DA’s interface 16 , in a so called
ontology view (Simões et al., 2012).
Lexical-semantic network
PAPEL (Gonçalo Oliveira et al., 2008, 2009, 2010b) is a public domain lexical resource
with instances of several types of semantic relations, extracted automatically
from Dicionário PRO da Língua Portuguesa (DLP, 2005), a Portuguese dictionary,
property of Porto Editora. It was developed by Linguateca. The main differences
between PAPEL and a wordnet is that PAPEL was created automatically and is
not structured in synsets, nor sense-aware. PAPEL can be seen as a lexical network
– it is structured in relational triples t = {w1, R, w2} denoting instances of semantic
relations R, where w1 and w2 are lexical items, identified by their orthographical
form. Its current version, PAPEL 3.0 17 , contains about 190,000 triples of different
types, connecting about 100,000 unique lexical items.
Portuguese LKBs in numbers
Similarly to what we have done for the English LKBs, here, we put the Portuguese
LKBs side-by-side. Table 3.3 characterises the LKBs according to their construction
and availability. Table 3.4 shows the number of included lexical items, according
to their POS. Especially due to its automatic construction, PAPEL is clearly the
13 Available from http://openthesaurus.caixamagica.pt/ (August 2012)
14 See http://www.openoffice.org/ (August 2012)
15 Available from http://pt.wiktionary.org/ (August 2012)
16 Available from http://www.dicionario-aberto.net/ (August 2012)
17 Available from http://www.linguateca.pt/PAPEL/ (August 2012)