<?xml version="1.0" standalone="yes"?>
<Paper uid="A83-1013">
  <Title>III ANALYSIS</Title>
  <Section position="3" start_page="0" end_page="0" type="intro">
    <SectionTitle>
I I~TRODUC'TION
</SectionTitle>
    <Paragraph position="0"> Following the developmemt 0PS various front ends for natural language access to databases, it is now generally agreed that such a front end must utillse at least three different kinds of knowledge to accomplish its task: linguistic k~owledge, knowledge of the domain of discourse, and knowledge of the organlsational structure of the database. Thus broadly speaking, a user request to the database goes through three conceptually different forms: the output of linguistic analysis oPS the question, its representation in terms of the domain's conceptual schema, and its interpretation in the database access language. Early natural language front ends usually did not have a clearcut separation between the different stages of the process: for example LUNAR (Woods 1972) merged the domain model and the database model into one, and systems such as the early incarnation of LADDER (Hendrix et al 1978) and PLANES (Waltz 1978) made heavy use of semantic grammars with their domain-dependent lexicons ccmbinin8 linguistic kncwledge with domain knowledge and so merging the first two stages. None 0PS these systems, moreover, made any significant use of ~eneral, as opposed to domain-specific, semantic information.</Paragraph>
    <Paragraph position="1"> In an attempt to achieve portability from one database to another, mcst current systems adhere to a ~eneral framework (Konolige 1979), which makes a clear distinction between the different processing phases and distinguishes the domain-dependent from the domaln-independent parts of the front end, and also domain operations from database management cperatlons. However semantic processing is still This work is supported by the U.K. Science and Engineering Research Council.  essentially driven by domain-dependent semantics.</Paragraph>
    <Paragraph position="2"> Linguistic processing is therefore primarily syntactic parsing, and relating general linguistic to specific domain knowledge within the framework of a modular front end takes the form of applying domain-dependent semantic processing to the output of the syntactic parser. This may be done in a slmple, minded way as in PHLIQAI (Bronnenberg et al 1979) and T~ (Damerau 1980), or by providing hooks in the syntactic representation (domain-independent calls to semantic operators which will evaluate differently in dlPSferent contexts), as in DIALOGIC (Grosz et ai 1982). In either case the usual unhappy consequence oPS separating syntactic and semantic processing, namely the hassle of manipulating alternative syntactic trees, follows. Furthermore, changlngdomalns implies changing the definitions of the semantic operators, which are procedural in nature, while it may be preferable to keep the domain-dependent parts of the front end in declarative form, as is indeed done in (Warren and Pereira 1981).</Paragraph>
    <Paragraph position="3"> Thus in systems of this by now conventional type, the 'portability' achieved by confining the necessary domain-dependent semantic processing to well-defined modules is purchased at the heavy price of limiting the early linguistic processing to syntax, and, perhaps, some very global and undiscriminating semantics (see for example the sccping algorithm of (Grosz et al 1982)).</Paragraph>
  </Section>
class="xml-element"></Paper>