Utility for communicability by profit and cost of agreement

The inflection of words based on agreement, such as number, gender and case, is considered to contribute to clarify the dependency between words in a sentence. Our purpose in this study is to investigate the efficiency of word inflections with HPSG (Head–driven Phrase Structure Grammar), which is able to deal with these features directly. Using a notion of utility, we measure the efficiency of a grammar in terms of the balance between the number of semantic structures of a sentence, and the cost of agreement according to the number of unification processes. In our experiments, we showed how these were balanced in two different corpora. One, WSJ (Wall Street Journal), includes long and complicated sentences, while the other corpus, ATIS (Air Travel Information System) does shorter colloquial sentences. In the both corpora, agreement is surely important to reduce ambiguity. However, the importance of agreement in the ATIS corpus became salient as personal pronouns were so often employed in it, compared with the WSJ corpus.