An HPSG Parser Based on Description Logics

An HPSG Parser Based on Description l,ogies* J. Joachim Quantz Technische Universit~it Berlin, ]'rojekt KHZVM11, FR 5-d 2, Franklinstr. 28/29, D-10587 Berlin, Germany, e-mail: jjq @cs.tu-berlin.de Abstract Ira this paper I present a parser based on De- scription Logics (I)I.) for a German lll'SG-slyle fragment. The specilied parser relies mainly on the inferential capabilities of the nnderlying DL system. Given a preferential default ex- tension for DL disamhiguation is achieved by choosing the parse containing a qualitatively minimal number of exceptions. 1 Introduction Ira tiffs paper I present a parser for IIP'SO based on De- scription Logics (1)1.). "l)m main mntiwrtion for specifying such it parser relies on considerations concerning the dis- ambiguation of NL expressions. In ISchmitz, Quantz 931 it is shown how different types of ambigtfity can be han- dled will) a homogeneous approach based on lhe notion of preference rules lJackendoff 83]. A major reqnirement for such a t,nified approach is that information usually rep- resented rather differently (e.g. syntactic, semantic, and encyclopedic information) is homogeneously represented in it tin;fern1 and declarative formalism in order to express and evaluate the complex l)references stemming from the different kinds of information. Description Imgics have been developed ira the field of Knowledge Representation (see, for example, [Brachman et al. 91]). qtrey have already been used for the representation of semantic and encyclopedic information, e.g. IAllgayer et al. 89, Stock 91, Preuss el al. 921. Due 1(5 their similarity to typcd feature formalisms [Carpenler 921, syntactic infonnation is in principle also expressible in DI,, as already sketched in [Quanlz 93, Quantz, Sehmilz 941. Furlhermore, Preferential Defaull Description Logics (H)DL) based on weighted defaults [Quuntz, Ryan 931 can be used to represent the preference rules in a declarative and formally well-founded way. ht the following I will mainly show how IIl,'SG-slyle syntactic information can be represented in 1)I., atrld bow a simple parser can be build by using tim inference capabil- ities of a DL system. Note that when specifying the parser I will kee t) the presentation as simple as possible, thereby deliberately ignoring efficiency aspects. I will also refrain from model;riga//aspccts of relevant knowledge in DL, i.e. there are still pieces of information which are not explic- itly encoded in the DL modeling, but tire rather ;nil;licitly cnntained in lhe parser (e.g. information related to linear precedence and to traces}. The main objective of this paper it thus neilher to con- tribute to research in efficient parsing tectmology, nor to "The project KIT-VM11 is suppo21ed by lhe German leedcral Minister of Research and Technology (BMFF) under conh'ac101 IV 101Q8. develop a declarative formalism ira which all aspects rele- vant for NI.P can be represented. It is rather to prnvide the b'ilsis for an implementation of the exception minimiza- lion aplsroach to interpretation proposed in IQuantz 931. In Section 6 I will hriefly sketch how the l)L-based parser l)resenled in Section 5 can be exleuded to realize this ap- proach. 2 ilasie Ideas An important distinction made in DI., but missing …

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