The semantic component of the grammar produces (simplified) Quasi-Logical Forms [2]. These are linguistically motivated, domain-independent representations of the meaning of utterances.
QLFs allow considerable underspecification. This is convenient in this application because most ambiguities that arise, such as ambiguities of scope, do not need to be resolved. These QLFs are translated into domain-specific ``updates'' to be passed on to the dialogue manager (DM) for further processing. The DM keeps track of the information provided by the user by maintaining an information state or form. This form is a hierarchical structure, with slots and values for the origin and destination of a connection, for the time at which the user wants to arrive or depart, etc. The distinction between slots and values can be regarded as a special case of ground and focus distinction [9]. Updates specify the ground and focus of the user utterances. For example, the utterance ``No, I don't want to travel to Leiden but to Abcoude!'' yields the following update:
userwants.travel.destination.
([# place.town.leiden];
[! place.town.abcoude])
One important property of this representation is that it
allows encoding of speech-act information. The ``#'' in the update
means that the information between the square brackets (representing
the focus of the user-utterance) must be retracted, while the ``!''
denotes the corrected information.