Forming a set of facts about a piece of jewellery into a structure that yields a coherent text is a non-trivial problem. Much work in NLG makes the assumption that constructing something like an RS tree is a necessary step in the planning of a text. In this task, one is given a set of facts all of which should be included in a text and a set of relations between facts, some of which can be included in the text. Each relation has applicability conditions which can be tested between two atomic facts. For two complex text spans, a relation holds exactly when that relation holds between the nuclei of those spans.
Relations can thus hold between text spans of arbitrary size.
It can therefore be expected that it will produce very good results in restricted domains where limited text patterns are used, but that it will be hard to extend it to freer text types. The second idea is to use information about goals to limit possibilities. This second approach will work well if there are strong goals in the domain which really can influence textual decisions. This is not always the case. Marcu first of all attempts to find the best ordering of the facts.