LkbUnfilling

Overview

Unfilling of feature structures is the removal of redundant information from feature structures, in order to make them smaller. When only redundant information is removed, they contain precisely the same information as the original feature structures, but with less room.

One application for unfilling is the display of feature structures, such as the ones associated with chart edges. When they are displayed in full, they can be huge, but a lot of the information is redundant. Unfilled, the feature structure becomes much clearer.

The LKB menus that display feature structures have been extended with menu entries to display unfilled feature structures (in the "Parse Tree" and "Chart" windows). The best way to get familiar with unfilled feature structures is to compare a few with the unfilled variants.

As unfilling does not throw away any information from the feature structures, they can also be used for manual unification (as used for debugging). Note however that the results are not necessarily unfilled.

Unfilling More Technically

Unfilling is in some sense the opposite operation of "Expand type". The latter takes a type and make a feature structure out of it by recursively adding all constraints that have been defined with the used types. (Sometimes, this is called "filling".) Unfilling takes a feature structure and recursively removes all information that "Expand type" would have added (this is the redundant information). Unfilling an expanded type, for instance, returns a feature structure displaying only the type name (note though that it is not always that simple).