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1.5.3 Application areas
From the beginning Description Logics have been considered general purpose languages for knowledge representation and reasoning, and therefore suited for many applications. In particular, they were considered especially effective for those domains where the knowledge could be easily organized along a hierarchical structure, based on the “IS-A” relationship. The ability to represent and reason about taxonomies in Description Logics has motivated their use as a modeling language in the design and maintenance of large, hierarchically structured bodies of knowledge
as well as their adoption as the representation language for formal ontologies [Welty and Guarino, 2001].
We now briefly look at some other research areas that have a more general relationship with Description Logics. Such a relationship exists either because Description Logics are viewed as a basic representation language, as in the case of natural language processing, or because they can be used in a variety of ways in concert with the main technology of the area, as in the field of Database Management.
1.5.3.1 Natural language processing
Description Logics, as well as semantic networks and frames, originally had natural language processing as a major field for application (see for example [Brachman, 1979]). In particular, when work on Description Logics began, not only was a large part of the DL community working on natural language applications, but Description Logics also bore a strong similarity to other formalisms used in natural language work, such as for example [Nebel and Smolka, 1991].
The use of Description Logics in natural language processing is mainly concerned with the representation of semantic knowledge that can be used to convey meanings of sentences. Such knowledge is typically concerned with the meaning of words (the lexicon), and with context, that is, a representation of the situation and domain of discourse.
A significant body of work has been devoted to the problem of disambiguating different syntactic readings of sentences, based on semantic knowledge, a process called semantic interpretation. Moreover, semantic knowledge expressed in Description Logics has also been used to support natural language generation.
Since the domain of discourse for a natural language application can be arbitrarily broad, work on natural language has also involved the construction of ontologies [Welty and Guarino, 2001]. In addition, the expressiveness of natural language has led also to investigations concerning extensions of Description Logics, such as for example, default reasoning (see Chapter 6).
Several large projects for natural language processing based on the use of Description Logics have been undertaken, some reaching the level of industrially-deployed applications. They are referenced in Chapter 15, where the role of Description Logics in natural language processing is addressed in more detail.