## Reference Resolution

The Jet reference resolver resolves anaphoric references to noun phrases. It is intended to be invoked as the last step in processing each sentence in a document.

The input to reference resolution consists of a set of annotations of type constit with type=ngroup. These are called the 'mentions'. Each such annotation should have a pa feature giving its predicate-argument structure, and -- if its head is a name -- the feature isName with some non-null value.

The output of reference resolution is a set of annotations of type entity. Each entity annotation corresponds to a set of one or more mentions which are deemed to be coreferential. The entity annotation has the features head, position, mentions, number, name, and human.

Mentions are resolved as follows:

- a common noun mention is resolved with the closest prior mention with the same head, or with a head which is associated with the same concept or a more specific concept in the concept hierarchy
- a name mention is resolved with the closest prior mention with the same name, or a superstring of the current name (so that, for example, "Bush" will be resolved with "George Bush")
- a third-person pronoun mention ("he", "she", "it", "they", "him", "her", "them") will be resolved with the closest prior mention which agrees with the pronoun in number and human-ness (antecedents of "he", "she", "him", and "her" must be human; antecedents of "it" must not be human). Human-ness for nouns is based on the human feature in the predicate-argument structure; for names, person names are considered human, while other names are considered non-human. This classification is slightly incorrect since the dictionary labels an entry as human if any sense (not necessarily the most common sense) of that entry is human.
- a first- or second- person pronoun is resolved with the closest prior mention of the same pronoun

If no prior mention satisfies the given constraints, a new entity is created.

In addition, after mentions are resolved, reference resolution searches for annotations of type event. For each event, it generates an annotation of type r-event which is identical except that any feature whose value is a mention (ngroup) is replaced by the entity to which the mention was resolved.