Metagrammar engineering: Towards systematic exploration of implemented grammars

Proceedings of the 49th Annual Meeting of the Association for Computational Linguistics, pages 1066–1076, Portland, Oregon, June 19-24, 2011. c⃝2011 Association for Computational Linguistics Metagrammar Engineering: Towards systematic exploration of implemented grammars Antske Fokkens Department of Computational Linguistics, Saarland University & German Research Center for Artificial Intelligence (DFKI) Project Office Berlin Alt-Moabit 91c, 10559 Berlin, Germany afokkens@coli.uni-saarland.de Abstract When designing grammars of natural lan- guage, typically, more than one formal anal- ysis can account for a given phenomenon. Moreover, because analyses interact, the choices made by the engineer influence the possibilities available in further grammar de- velopment. The order in which phenomena are treated may therefore have a major impact on the resulting grammar. This paper proposes to tackle this problem by using metagrammar development as a methodology for grammar engineering. I argue that metagrammar engi- neering as an approach facilitates the system- atic exploration of grammars through compar- ison of competing analyses. The idea is illus- trated through a comparative study of auxil- iary structures in HPSG-based grammars for German and Dutch. Auxiliaries form a cen- tral phenomenon of German and Dutch and are likely to influence many components of the grammar. This study shows that a spe- cial auxiliary+verb construction significantly improves efficiency compared to the standard argument-composition analysis for both pars- ing and generation. 1 Introduction One of the challenges in designing grammars of nat- ural language is that, typically, more than one for- mal analysis can account for a given phenomenon. The criteria for choosing between competing analy- ses are fairly clear (observational adequacy, analyti- cal clarity, efficiency), but given that analyses of dif- ferent phenomena interact, actually evaluating anal- yses on those criteria in a systematic manner is far from straightforward. The standard methodology in- volves either picking one analysis, and seeing how it goes, then backing out if it does not work out, or laboriously adapting a grammar to two versions supporting different analyses (Bender, 2010). The former approach is not in any way systematic, in- creasing the risk that the grammar is far from opti- mal in terms of efficiency. The latter approach po- tentially causes the grammar engineer an amount of work that will not scale for considering many differ- ent phenomena. This paper proposes a more systematic and tractable alternative to grammar development: meta- grammar engineering. I use “metagrammar” as a generic term to refer to a system that can generate implemented grammars. The key idea is that the grammar engineer adds alternative plausable anal- yses for linguistic phenomena to a metagrammar. This metagrammar can generate all possible com- binations of these analyses automatically, creating different versions of a grammar that cover the same phenomena. The engineer can test directly how competing analyses for different phenomena inter- act, and determine which combinations are possible (after minor adaptations) and which analyses are in- compatible. The idea of metagrammar engineering is illus- trated here through a case study of word order and auxiliaries in Germanic languages, which forms the second goal of this …

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