CUF - A Formalism for Linguistic Knowledge Representation

We describe the formalism CUF (Comprehensive Uniication Formalism), which has been designed as a tool for writing and making computational use of any kind of linguistic description ranging from phonology to pragmatics. The motivations for its major design decisions are discussed. CUF is an oospring of the line of theory-neutral universal grammar formalisms like PATR-II SUP + 83] and STUF-II BKU88, DD or91, DR91]. Like these it is based on deening feature structures and relations over these as encodings of linguistic principles and data. However, it is radically more expressive, since it allows the deenition of arbitrary recursive relational dependencies without tying recursion to phrase structure rules. Complex restrictions needed in semantic interpretation like anaphora resolution and presupposition checking can thus be stated in the same description language as the syntactic restrictions, providing the basis for highly integrated linguistic processing. CUF can be roughly characterized as a feature structure description language similar to Kasper/Rounds logic KR90] combined with the possibility of stating deenite clauses over feature terms. Moreover, feature structures are typed, with the types possibly being ordered in a hierarchy. The CUF type discipline allows for an axiomatic statement of global restrictions on the structures in which the program is to be interpreted providing enough redundancy in the descriptions to detect mistakes without burdening the grammar writer with tedious repetitions. Although it is useful to think of CUF as a kind of pure (typed) in which rst-order terms have been replaced by feature terms, there are two important respects in which this analogy is misleading. First of all, CUF makes a clear distinction between the purely declarative logical speciication and the control statements which are used to guide the proof procedure without compromising the logical semantics of the speciication. Second, we use a syntax especially well suited for a direct description of feature structures. The connection to logic programming can be explored even further by taking into account that CUF is an instance of constraint-logic programming (CLP) of the very general HH ohfeld/Smolka scheme HS88]. This provides us not only with a sound and complete proof procedure, but also equips us with the right paradigm to attack the eeciency problems associated with highly modular speciications, as for instance proposed by GB theory.