Partially Specified Signatures: A Vehicle for Grammar Modularity

Proceedings of the 21st International Conference on Computational Linguistics and 44th Annual Meeting of the ACL, pages 145–152, Sydney, July 2006. c⃝2006 Association for Computational Linguistics Partially Specified Signatures: a Vehicle for Grammar Modularity Yael Cohen-Sygal Dept. of Computer Science University of Haifa yaelc@cs.haifa.ac.il Shuly Wintner Dept. of Computer Science University of Haifa shuly@cs.haifa.ac.il Abstract This work provides the essential founda- tions for modular construction of (typed) unification grammars for natural lan- guages. Much of the information in such grammars is encoded in the signature, and hence the key is facilitating a modularized development of type signatures. We intro- duce a definition of signature modules and show how two modules combine. Our def- initions are motivated by the actual needs of grammar developers obtained through a careful examination of large scale gram- mars. We show that our definitions meet these needs by conforming to a detailed set of desiderata. 1 Introduction Development of large scale grammars for natural languages is an active area of research in human language technology. Such grammars are devel- oped not only for purposes of theoretical linguis- tic research, but also for natural language applica- tions such as machine translation, speech genera- tion, etc. Wide-coverage grammars are being de- veloped for various languages (Oepen et al., 2002; Hinrichs et al., 2004; Bender et al., 2005; King et al., 2005) in several theoretical frameworks, e.g., LFG (Dalrymple, 2001) and HPSG (Pollard and Sag, 1994). Grammar development is a complex enterprise: it is not unusual for a single grammar to be devel- oped by a team including several linguists, com- putational linguists and computer scientists. The scale of grammars is overwhelming: for exam- ple, the English resource grammar (Copestake and Flickinger, 2000) includes thousands of types. This raises problems reminiscent of those encoun- tered in large-scale software development. Yet while software engineering provides adequate so- lutions for the programmer, no grammar develop- ment environment supports even the most basic needs, such as grammar modularization, combi- nation of sub-grammars, separate compilation and automatic linkage of grammars, information en- capsulation, etc. This work provides the essential foundations for modular construction of signatures in typed unifi- cation grammars. After a review of some basic notions and a survey of related work we list a set of desiderata in section 4, which leads to a defi- nition of signature modules in section 5. In sec- tion 6 we show how two modules are combined, outlining the mathematical properties of the com- bination (proofs are suppressed for lack of space). Extending the resulting module to a stand-alone type signature is the topic of section 7. We con- clude with suggestions for future research. 2 Type signatures We assume familiarity with theories of (typed) unification grammars, as formulated by, e.g., Car- penter (1992) and Penn (2000). The definitions in this section set the notation and recall basic no- tions. For a partial function F, ‘F(x)↓’ means that F is defined for the value x. Definition 1 Given a partially ordered set ⟨P, ≤⟩, the …

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