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Non-S constituents

Although sentential trees are generally considered to be special cases in any grammar, insofar as they make up a `starting category', it is the case that any initial tree constitutes a phrasal constituent. These initial trees may have substitution nodes that need to be filled (by other initial trees), and may be modified by adjunct trees, exactly as the trees rooted in S. Although grouping is possible according to the heads or anchors of these trees, we have not found any classification similar to the subcategorization frames for verbs that can be used by a lexical entry to create a tree family of the set of trees selected by such entries. These trees are selected one by one by each lexical item, according to each lexical item's idiosyncrasies. The grammar described by this technical report places them into several files for ease of use, but these files do not constitute tree families in the way that the subcategorization frames do.

XTAG Project
http://www.cis.upenn.edu/~xtag