DISCO-An HPSG-based NLP System and its Application for Appointment Scheduling Project Note

and DISCO -- An HPSG-based NLP System its Application for Appointment Scheduling -- Project Note -- Hans Uszkoreit, Roll Backofen, Stephan Busemann, Abdel Kader Diagne, Elizabeth A. Hinkelman, Walter Kasper, Bernd Kiefer, Hans-Ulrich Krieger, Klaus Netter, Gfinter Neumann, Stephan Oepen, Stephen P. Spackman German Research Center for Artificial Intelligence (DFI(I) Stuhlsatzenhausweg 3, 66123 Saarbrficken, Germany (name}~dfki,. uni-sb, de Abstract The natural language system DISC() is described. It combines a powerful and flexible grammar development system; • linguistic competence for German including morphol- ogy, syntax and semantics; • new metlmds for linguistic performance modelling on the basis of high-level competence grammars; • new methods for modelling multi-agent dialogue com- petence; • an interesting sample application for appointment scheduling and calendar management. 1 Introduction We will describe results of a project in natural lan- guage research carried out during the last four years at, the German Research Center for Artiticial Intelligence in Saarbrficken. All system l)uilding took place dur- ing the last three years. The special approach of this project is a combination of linguistically sound high- levcl grammatical description and specialized methods for linguistic performance modelling. During the last decade it has become obvious to the majority of researchers in our field that the linguis- tically designed elegant and transparent grammars written in high-level representation languages such as HPSG or LFG could not be employed for elficient and robust processing in a straightforward way. Many researchers have therefore resorted to well- known older methods such as ATNs or other augment- ed finite-state methods, to statistical or connectionist methods, or to combinations of these. Several projects participating in the demanding ARPA competitions fall in this category. Many others have decided to settle for a com- promise between high-level description and efficient processing by strongly constraining their formalisms. The resulting formalisms are usually much closer to PROLOG and do not contain a powerful multiple- inheritance type system; e.g. the Core Language En- gine (CLE) of SRI Cambridge [1], its derNative tile GEMINI system of SRI International in Menlo Park, the LKP of SIEMENS in Munich [3]. As a conse- quence of their design philosophy, these systems usu- ally do not feature a powerthl development platlbrm. Only a few groups have continued to work ill high- level formalisms driven by the expectation that better processing methods for these formalisms can be de- veloped. Our work belongs in this category, tIowever, we have decided to allow for combinations of high- level grammatical description and low-level processing methods by strictly distinguishing between a gener- al linguistic competence model and very applic~tion- specific performance models. Our decision was based on some fundamental crite- ria: • It, is necessary to build general, reusable compe- tence systems that can be the basis lbr different applications, since the development of liuguistic eoml)etenee is too costly to redo for each new ap- plication. • In the foreseeable future, NL applications will have very limited linguistic competence, where the limitations depend on the task to be per- formed. They determine coverage and …

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