Finite automata for compact representation of tuple dictionaries

A generalization of the dictionary data structure is described, called tuple dictionary. A tuple dictionary represents the mapping of n-tuples of strings to some value. This data structure is motivated by practical applications in speech and language processing, in which very large instances of tuple dictionaries are used to represent language models. A technique for compact representation of tuple dictionaries is presented. The technique can be seen as an application and extension of perfect hashing by means of finite-state automata. Preliminary practical experiments indicate that the technique yields considerable and important space savings of up to 90% in practice.