Mihai Ciocoiu, Štefan Bruda * GULiveR: Generalized Unification Based LR Parser for Natural Languages




For a faster production retrieval in grammar and also for a better efficiency of any unification, structured categories are implicitly indexed by "cat" attribute: any unification (or dag retrieval which is basically a set of unifications) verifies first the equality of the value of that attribute in the two dags; if the two values do not match then the unification fails immediately.

The unification is a very important process in any parser. Even if we used in our application one of the most efficient algorithms, we are currently testing another dag representation which uses binary trees and lazy evaluation [17] (the dags in that representation also shares structures and allow an efficient duplication). This representation does not use an environment structure and therefore may be more appropriate to our application. Anyway, no comparisons are yet available.

The initial project included a minimal interface because a parser cannot be a stand alone program (it can be used either for natural language understanding or machine translation). We included later a graphical interface (Macintosh) for didactic purposes (because PAIL is first of all a didactic system). This interface offers possibilities to view the parse forest (figure 5), to trace the execution (figure 3) and to view the parse table (figure 1). The application offers an exhaustive base for compositional semantic analysis by the parse forest produced, and is fast enough to be useful on such a small platform as the Mac.

We tested the parser using a small grammar which models the enunciative English phrases. We intend to use the application for a complete Romanian grammar.

Acknowledgments. Special thanks to Dr. Dan Tufi who helped us to bring up to life this project. Without his comments and advice this paper would not have been the same.

References

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  15. O. POPESCU, D. TUFIª, V. MIHALACHE, A. BOANGIU, Modelare cognitiva a limbajelor naturale, ICI, 1993.

  16. M. ROSNER, P. CATTANEO, D. TUFIª, On-Line Summer School on AI Technology Ongoing Swiss-Romanian Cooperation, in ELSNews, January 1995.

  17. L. KARTTUNEN, M. KAY, Structure Sharing with Binary Trees, in More Notes from the Unification Underground - A Second Compilation of Papers on Unification-Based Grammar Formalisms, SRI International, 1985.



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