Some Remarks on the Decidability of the Generation Problem in LFG- and PATR-Style Unification Grammars

In this paper, we prove the decidability of the generation problem for those unification grammars which are based on contextfree phrase structure rule skeletons, like e.g. LFG and PATR-II. The result shows a perhaps unexpected asymmetry, since it is valid also for those unification grammars whose parsing problem is undecidable, e.g. grammars which do not satisfy the off-line parsability constraint. The general proof is achieved by showing that the space of the derivations which have to be considered in order to decide the problem for a given input is always restricted to derivations whose length is limited by some fixed upper bound which is determined relative to the "size" of the input