Memoisation in sentence generation with lexicalised grammars

This paper discusses a sentence generation system PROTECTOR which uses: (i) a non-hierarchical semantic representation which allows for flexible lexical choice and un~form treatment of different languages, (ii) a lexicalised D-Tree Grammar which is very similar to TreeAdjoining Grammar in spirit, and {iii) dynamic programming techniques to avoid doing redundant computations. We review the motivation for choosing such an organisation of the generalion syslem and give an example of the generation of a sentence which involves a lexical gap. The generation of the example sentence requires a nondeterministic mode of computation (the lexical gap forcing backtracking) . We show how dynamic programming techniques can be used to save re-generating structures using a top-down generation algorithm.