  This paper is focused on the language modelling for task-oriented domains and
presents an accurate analysis of the utterances acquired by the Dialogos spoken
dialogue system. Dialogos allows access to the Italian Railways timetable by
using the telephone over the public network. The language modelling aspects of
specificity and behaviour to rare events are studied. A technique for getting a
language model more robust, based on sentences generated by grammars, is
presented. Experimental results show the benefit of the proposed technique. The
increment of performance between language models created using grammars and
usual ones, is higher when the amount of training material is limited.
Therefore this technique can give an advantage especially for the development
of language models in a new domain.
