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

32 Chapter 3. Related Work
knowledge about the world and common-sense knowledge, which can be defined as
knowledge that an ordinary person is expected to know. An important feature of
common-sense knowledge bases is that they are typically very formalised, which
eases their representation as ontologies and provides reasoning capabilities.
Popular LKBs in numbers
In order to have an idea on the size and contents of the popular LKBs, tables 3.1
and 3.2 contain quantitative information about them. Table 3.1 shows the number of
lexical items included in each LKB, according to their POS. Table 3.2 indicates the
core structure of each LKB, the number of instances of that structure, the number
of different types of relation that may connect two core structures, and the unique
types of the later relations. When the information in the table cells is missing, it is
not applicable. For WordNet, the number of relations includes the direct and the
inverse relations, because they have different names. On the other hand, MindNet
identifies direct and inverse relations by a directed arrow (e.g. ←Hyp and Hyp→,
repectively for hypernymy and hyponymy). So, in front of the number of MindNet
relations, we added the information ’×2’.
Due to its different structure, it is not possible to compare MindNet, created
automatically, with the other LKBs, all handcrafted. The only number that shows
that MindNet is larger is the number of relation instances (713k), which is significantly
higher than in WordNet 3.0 (285k). Moreover, as an automatic approach,
MindNet can also grow by processing more text. Richardson et al. (1998) refer that,
after processing the Microsoft Encarta 98 encyclopedia, 220k additional headwords
were collected for MindNet. Also, the MindNet website currently refers a total of
45 different relation types, which is more than the 32 reported in 1998.
These numbers also show that LKBs are much smaller than knowledge bases as
DBPedia (more than 2.5M concepts and 250M relations) and Freebase (Bollacker
et al., 2008), a collaborative knowledge base (more than 20M concepts and 300M
relations). This occurs especially because LKBs are restricted to lexical knowledge,
while the others are much broader and contain a wide-range of world knowledge
facts.
Resource Lexical items
Nouns Verbs Adjectives Adverbs Other Total
WordNet 3.0 (2006) 117,097 11,488 22,141 4,601 - 155,327
MindNet (1998) - - - - - 159,000 headwords
FrameNet (2012) 5,136 4,819 2,268 - 378 12,601
VerbNet (2012) - 3,769 - - - 3,769
Table 3.1: Comparison of LKBs according to included lexical items.
Resource Core structure Relations
Type Instances Unique Types Instances
WordNet 3.0 (2006) synset 117k+ 20 285k
MindNet (1998) word entry 191k definitions 32 (×2) 713k
FrameNet (2012) frame 1,674 8 -
VerbNet (2012) class entry 274 - -
Table 3.2: Comparison of LKBs according to core structure and relations.