Controlling Content Realization with Functional Unification Grammars

Standard Functional Unification Grammars (FUGs) provide a structurally guided top-down control regime for sentence generation. When using FUGs to perform content realization as a whole, including lexical choice, this regime is no longer appropriate for two reasons: (1) the unification of non-lexicalized semantic input with an integrated lexico-grammar requires mapping "floating" semantic elements which can trigger extensive backtracking and (2) lexical choice requires accessing external constraint sources on demand to preserve the modularity between conceptual and linguistic knowledge. We introduce two control tools that we have implemented for FUGs to address these limitations: bk-class, a form of dependency-directed backtracking to efficiently process "floating" constraints and external, a co-routine mechanism allowing a FUG to cooperate with external constraint sources during unification. We show how these tools complement the top-down regime of FUGs to control the whole content realization process