However, a system of this kind which sets up a network of hyperlinks in its entirety in response to a single query from the user, will not be able to take full advantage of a dynamic user-model. The ideal may be a system where pages and links are created one by one, and the user has the opportunity for input at every stage. The theory of user modelling in NLG is still at a relatively early stage of development. From the user's point of view, there is a degree of flexibility in the system even if the hypertext is fully generated in advance, because he has a choice about what to look at next. In some systems, all the possible texts have been anticipated explicitly in advance, even though the detailed contents may be dynamically generated.
More flexibility is offered if the text produced depends on a set of independent dimensions.
PEBA-II has similar flexibility, in that its comparison texts depend on two animals that are chosen by the user independently. This potential freedom may not be obvious or available to the user, however. Just as a speaker must allow a hearer opportunity to respond, it is important for the system to generate a fair selection of new links to explore, to ensure that the reader finds something to his liking. In ILEX-0, the user is able to pick any object in the gallery to look at next, which is intended to allow the same kind of random movement that a user might make in a real museum gallery. On the other hand, it might also be important not to generate too many links to follow up, as this might make navigation confusing.