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

18 Chapter 2. Background Knowledge
Taxonomies
A taxonomy is a special kind of lexical network, structured according to certain
rules. In a taxonomy, nodes represent concepts, eventually described by lexical
items, and (directed) edges are relations connecting the former with their superordinates.
It can be seen as a hierarchical tree where the higher nodes are more generic
and the lower are more specific. In other words, a taxonomy is a classification of a
certain group of entities, such as plants, academical degrees or musical genres, often
used to represent hierarchical relations. For instance, in the case of hypernymy, each
node inherits all the properties of its superordinate. Figure 2.9 illustrates this kind
of network with a hypernymy taxonomy of animals.
Figure 2.9: Example of a taxonomy of animals, adapted from Cruse (1986).
More on taxonomies can be found in Cruse (1986), where considerations about
these structures and properties that they should hold are discussed and integrated
in his view on lexical semantics. Furthermore, Smith (2001) lists the principles for
taxonomy well-formedness, in the context of ontologies and information systems.
Conceptual graphs
Conceptual graphs (Sowa, 1992) are a formalism for expressing meaning, commonly
used in topics that go from databases and expert systems to AI and NLP.
Conceptual graphs typically represent first-order logic formulas. They contain two
kinds of nodes: rectangular boxes and ovals, which denote, respectively, concepts
and relations. Figure 2.10, shows a conceptual graph representation for the meaning
of sentence:
John is going to Boston by bus.
Figure 2.10: Conceptual graph, from http://www.jfsowa.com (September 2012).