Focus Spaces

Apart from the text-planner's specification of the NP-form, the text-planner also maintains some variables concerning the current referring environment, mainly in terms of various focus spaces. These various spaces are:

1. Mentioned Entities: entities mentioned at some point within the discourse.
2. Shared Entities: entities which the system assumes the addressee to know about. These entities include world-knowledge (e.g., Ronald Reagan), but also entities mentioned previously in the discourse (mentioned-entities), and entities in the immediate context (focal-objects). Entities in this space are potential confusers for definite reference with the.
3. Focal Objects: the focal space includes a set of entities which may potentially be referred to as this x. Firstly, we have the Prior-Cb (backward looking centre, usually the subject of the prior sentence). Entities directly related to this may also be focal. This is also called the local focus in our system. Then there is the page-focus, the focus of the current object description in the ILEX system, e.g., this brooch. Other objects are also focal by being part of the immediate context of the reader/writer. In a web-browsing environment, this might include the current page (this page), or parts of the page (this picture).

In addition to the focal spaces, there are also variables holding individual focal objects, including the Cb and Prior-Cb, Page-Focus and Discourse-Focus. We allow pronominalisation only when the object being referred to is Prior-Cb, which seems to produce coherent reference.