Malouf, R., J. Carroll and A. Copestake (2000) `Efficient feature structure operations without compilation', Natural Language Engineering, 6(1). 29-46.
One major obstacle to efficient processing of large wide coverage grammars in
unification-based grammatical frameworks such as \hpsg\ is the time and space
cost of the unification operation itself. In a grammar development system it
is not appropriate to address this problem with techniques which involve
lengthy compilation, since this slows down the edit-test-debug cycle. Nor is
it possible to radically restructure the grammar.
In this paper we describe novel extensions to an existing efficient
unification algorithm which improve its space and time behaviour
(without affecting its correctness) by substantially increasing the
amount of structure sharing that takes place.
We also describe a fast and automatically tunable pre-unification filter
(the `quick check') which in practice detects a large proportion of
unifications that if performed would fail.
Finally, we present an efficient algorithm for checking for subsumption
relationships between two feature structures; a special case of this
gives a fast equality test. The subsumption check is used in a parser
(described elsewhere in this volume) which `packs' local ambiguities to
avoid performing redundant sub-computations.
Article published in Natural Language Engineering. Download pre-final pdf version.