On the notion of uniqueness

On the notion of uniqueness * Joke Dorrepaal Onderzoeksinstituut voor Taal en Spraak 3512 JK Utrecht, The Netherlands Email: Joke.Dorrepaal@let.ruu.nl Abstract In the paper it is argued that for some lin- guistic phenomena, current discourse repre- sentation structures are insufficiently fine- grained, both from the perspective of serv- ing as representation in NLP and from a truth conditional perspective. One such semantic phenomenon is uniqueness. It is demonstrated that certain elements are forced to have a unique interpretation, from a certain point in discourse onwards. This could be viewed as the semantic counter- part of surface order. Although it has al- ways been acknowledged that the left-to- right order of constituents influences the meaning of an utterance, it is, for exam- ple, not reflected in standard Discourse Representation Theory ([Kamp, 1981]). In the paper, an alternative representation for unique constituents will be proposed, re- sulting in asymmetry of certain conjoined conditions in a DRS-representation. Introduction Logic-based discourse theories are in many respects not sufficiently fine-grained. This becomes particu- larly obvious when we consider adopting such a rep- resentation as an interface in an NLP system. Suppose we have a discourse as in (1), and assign it a DRT-like representation as in (2): *The research reported here was supported by LRE project 061-62: Towards a Declarative Theory of Dis. course (sponsored by the European Community), and by Eurotra (sponsored by the EC and the NBBI). (1) John owns two talking parrots. Anne feeds them. (2) 3z y,z [ John=x & Anne=y ~ parrot(Z) & Zl=2 & owns(x,Z) & talk(Z) & feed(y,Z) ] When we take take this representation as a start- ing point for generation, we end up with at least the following discourses: (3) a b John owns two talking parrots. Anne feeds them. Anne feeds two parrots, which talk. John owns them. There are two parrots. They talk. John owns them and Anne feeds them. John owns two parrots, which talk. Anne feeds them. John owns two parrots that talk. Anne feeds them. The multiplicity of solutions in generation from semantic representations has often led to the conclu- sion that a purely logical representation is too weak to guide a generation process. This problem is of- ten 'solved' by incorporating syntactic knowledge in the semantic representation, or having the genera- tion process be guided by more than one source of knowledge. In many NLP-systems, for example, the semantic representation reflects the syntactic con- stituent structure of the string. One could also think of processing by correspondence (as proposed by [Ka- plan et al., 1989]), using different sources of infor- mation to guide the task. Below, it will be argued that these semantic representations are indeed too weak, but not only from the point of view of Nat- ural Language Processing. Some linguistic phenom- ena are not analysed adequately from a truth condi- tionM perspective either. 106 The phenomenon described in this paper, and ex- emplified in (3), touches on the notion of restrictive modification versus non-restrictive modification. I will …

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