Facts

A fact in ILEX represent a relation between two entities. These relations may be processual, e.g., that X made Y: maker(J-999, King01); or stative (e.g., that X is a type of Y: isa(j-999, generic-brooch).

Each fact is represented as an attribute-value structure as below:

Note that apart from the predicate and argument information, several other fields qualify the informational status of the fact, including the polarity (whether or not the relation holds), and defeasibility (distinguishing between hard facts about the entity, and those which are only tendencies, e.g., Art-Deco jewellery tends to be made of enamel (see Knott et al. 1997 for discussion of defeasibility in ILEX). The remaining fields, having a stronger affect on NP-planning, include:

• Assimilation: the degree to which the system considers the user to have understood the information. This is of particular importance to reference, since adequate reference usually requires the user to know the information used for reference (see later for exceptions).
• Importance/Interest: the degree to which the fact is considered important for the system to deliver to the user, and the system's estimate of the degree of interest to the user. These values are represented for each predicate type as a whole, and vary for different user models. These values are used when selecting the facts to use to produce a unique reference.