The paper demonstrates that exponential complexities with respect to grammar size and input length have little impact on the performance of three unification-based parsing algorithms, using a wide-coverage grammar. The results imply that the study and optimisation of unification-based parsing must rely on empirical data until complexity theory can more accurately predict the practical behaviour of such parserQ. 1. I N T R O D U C T I O N General-purpose natural language (NL) analysis systems have recently started to use declarative unification-based sentence grammar formalisms; systems of this type include SRI's CLARE system (Alshawi et al
