5.1 Basic Coreference

*Most computational linguists* prefer *their* own parsers.

Note that a quantified noun phrase would also be linked to subsequent anaphors, outside the scope of quantification, through the usual relation of identity of coreference. Thus in the following text all three noun phrases would be linked:

*Every TV network* reported *its* profits yesterday. *They* plan to release full quarterly statements tomorrow.

By this rule, a pronoun in a relative clause which is bound to the head of the clause would get a coreference link to the entire NP. Thus, for

every man who knows his own mind

we would establish a coreference link between "his" and the entire noun phrase "every man who knows his own mind":

<COREF ID="1" MIN="man">every man who knows <COREF ID="2" REF="1" TYPE="IDENT">his <COREF>own mind</COREF>

Julius Caesar, the well-known emperor,

This identity of reference is to be represented by a coreference link between the appositional phrase, "the well-known emperor" and the ENTIRE noun phrase, "Julius Caesar, the well-known emperor":

<COREF ID="1" MIN="Julius Caesar">Julius Caesar, <COREF ID="2" REF="1" MIN="emperor" TYPE="IDENT"> the well-known emperor,</COREF></COREF>

The appositional phrase may be separated from the head by other modifiers. Thus

Peter Holland, 45, deputy general manager, ...

becomes

<COREF ID="1" MIN="Peter Holland">Peter Holland, 45, <COREF ID="2" REF="1" TYPE="IDENT" MIN="manager"> deputy general manager,</COREF></COREF>

Bill Clinton is the President of the United States.

we would record a coreference link between "Bill Clinton" and "the President of the United States". Coreference should NOT be recorded if the text only asserts the possibility of identity between two markables. In

Phinneas Flounder may be the dumbest man who ever lived.

no coreference is to be recorded.

Two markables should be recorded as coreferential if the text asserts them to be coreferential at ANY TIME. Thus

Henry Higgins, who was formerly sales director for Sudsy Soaps, became president of Dreamy Detergents

should be annotated as

<COREF ID="1" MIN="Henry Higgins">Henry Higgins, who was formerly <COREF ID="2" MIN="director" REF="1" TYPE="IDENT">sales director for Sudsy Soaps,</COREF></COREF> became <COREF ID="3" MIN="president" REF="1" TYPE="IDENT">president of Dreamy Detergents</COREF>

...*producers* don't like to see a hit wine increase in price ... *Producers* have seen this market opening up and *they*'re now creating wines that appeal to these people.

"producers", "Producers", and "they" refer to types and they all refer to the same type. Notice that if interpreted as referring to sets, they would not all refer to the same set. More properly, there is no reason to think they would corefer; not all the producers who have seen the market opening up have created new wines.

Note that a type can be referred to by a bare plural, a definite singular np ("the tiger is fast becoming extinct") or a (bare) prenominal. In

The action followed by one day an Intelogic announcement that it will retain an investment banker to explore alternatives "to maximize *shareholder* value," including the possible sale of the company. Mr. Edelman declined to specify what prompted the recent moves, saying they are meant only to benefit *shareholders* when "the company is on a roll."

the two starred occurrences corefer to the type: shareholder (of Intelogic).

GM announced *its third quarter profit*. *It* was *$0.02*.

all three starred phrases refer to an amount of money; they all refer to the same amount of money. Hence they are coreferential. The first phrase, in context, refers to that amount via referring to a function, say of companies and quarters of a year--or times. (In addition, the "its" in the first NP would be linked to GM.) In

General Motors announced {their third quarter profit of *$0.02*}.

the bracketed and starred phrases are coreferential. They refer to one and the same amount of money. Note that here, as in the case of apposition, the result is that a phrase is marked as being coreferential with a part of the phrase. In

|*The temperature* is *90*....The temperature is rising.

the first occurrence of "the temperature" refers to the value of the function at arguments (places, times) supplied by context. That occurrence is coreferential with "90". In the second occurrence, "the temperature" refers to the function (indirectly, by way of referring to the derivative of the function). So it is not coreferential with the first occurrence or with "90".

There will be cases where a phrase could arguably refer to either a set or a type; in such ambiguous cases, the coreference should be recorded but marked as optional.

(1) *The White House* sent its health care proposal to Congress yesterday. Senator Dole said *the administration*'s bill had little chance of passing.

(2) *Ford* announced a new product line yesterday. *Ford* spokesman John Smith said *they* will start manufacturing widgets.

(3) I bought the New York Times this morning. I read that the editor of the New York Times is resigning.

(4) *The United States* is a democracy. *The United States* has an area of 3.5 million square miles.

We propose that coreference be determined with respect to coerced entities. Of course, this still leaves open the question as to the circumstances under which coercion is required. In (1) there is a coercion from the White House to the administration operating out of the White House, and that is IDENT with "the administration"; so "White House" and "administration" are IDENT. (Notice that there is also a question as to whether the adminstration's proposal is the same as its bill. This too requires a coercion of sorts.) In (2), while there might seem to be a coercion from Ford to a spokesman for Ford, we believe that such a coercion is not necessary, for it is plausible that corporations, as legal persons, can do many of the things that people can do--such as `announce'. They may have to do some or all such things through other agents, but many people do many things that way. And if Ford can announce, then it, through one of its spokesmen, can "say". Believing that no coercion is required, we would mark as coreferential the first instance of "Ford", the second instance of "Ford" (in the phrase "Ford spokesman John Smith"), and "they", but would NOT mark the phrase "Ford spokesman John Smith" as coreferential with anything else in this passage. In (3) the first "New York Times" is coerced into a copy of the paper published by the New York Times and the second is coerced into the organization; so they are not IDENT. (4) is somewhat akin to (2). Countries are both geographical entities and governmental units. Thus, no coercion is necessary and the two starred occurrences are coreferential.

In the absence of general principles, a body of such decisions will need to be developed to codify the rules for coercion and coreference. In cases where there has been no clear precedent, the answer keys for formal evaluations will need to mark coreference as optional.