Two principles of parse preference
Jerry R. Hobbs, John Bear · 1990
this paper is first to present a compendium of many of these heuristics and secondly to propose two principles that seem to underlie the .heuristics. The first will be useful to researchers engaged in building grammars of similarly broad coverage. The second is of psychological interest and may be a guide for estimating parse preferences for newly discovered am- biguities for which we lack the expe.rience to decide among on a more empirical basis. The mechanism for implementing parse preference heuristics is quite simple. Terminal nodes of a parse tree acquire a score (usually 0) from the lexical entry for the word sense. When a nonterminal node of a parse tree is constructed, it is given an initial score which is the sum of the scores of its child nodes. Var- ious conditions are checked during the construction of the node and, as a result, a score Of 20, 10, 3, -3, -10, or 20 may be added to the initial score. The score of the parse is the score of its root node. The parses of ambiguous sentences are ranked according to their scores. Although simple, this method has been very successful. In this paper, however, rather than describe the heuristics in terms this detailed, we will describe them in terms of the preferences among the alternate structures that motivated our scoring schemes