On Paraphrase and Coreference

Paraphrase extraction and coreference resolution have applications in Question Answering, Information Extraction, Machine Translation, and so forth. Paraphrase pairs might be coreferential, and coreference relations are sometimes paraphrases. The two overlap considerably (Hirst 1981), but their definitionsmake them significantly different in essence: Paraphrasing concerns meaning, whereas coreference is about discourse referents. Thus, they do not always coincide. In the following example, b and d are both coreferent and paraphrastic, whereas a, c, e, f, and h are coreferent but not paraphrastic, and g and i are paraphrastic but not coreferent.