coref

Governing Category and Coreference: 

Governing Category and Coreference Dekang Lin Department of Computing Science University of Alberta

Constraints on Coreference Relationships: 

Constraints on Coreference Relationships John hurt himself *Miss Marple hurt himself John likes him John said Peter likes him She likes Susan She said Jan likes Susan

C-command: 

C-command C-command is a relationship between two nodes in a parse tree  c-commands  if 1.  does not dominate  2. the parent of  dominates   dominates  if  is an ancestor of  in the parse tree NP Det N’ N PP P NP AP N A a forecast of future returns

Binding: 

Binding A noun phrase  is bound to another noun phrase  if  and  are co-indexed (refer to the same entity)  c-commands . Examples John hurt himself John likes him John said Peter likes him She likes Susan She said Jan likes Susan

Classification of NPs: 

Classification of NPs NPs can be classified into the following categories according to their binding property: R-Expressions: Mary, the policeman, the company Pronominals: he, she, you, her, his, ... Reciprocals and reflexives: each other, himself, herself, ... Chomsky82: -anaphor +anaphor -pronominal R-expressions Refl/Recp +pronominal Pronominals PRO

Binding Theory: 

Binding Theory Tentative Definition: The local domain of phrase is the smallest clause that contains the phrase. Principle A: A NP with [+anaphor] must be bound within its local domain. Principle B: A NP with [+pronominal] must not be bound within its local domain. Principle C: A NP with [-anaphor -pronominal] must not be bound.

Examples: 

Examples John hurt himself John likes him John said Peter likes him She likes Susan She said Jan likes Susan *John thinks that himself is the best candidate John considered himself to be the best candidate John said that pictures of himself were on sale. Peter read John’s story about himself/him. *John wanted Mary to take a picture of himself.

Government: 

Government Government is a relationship between two nodes in a parse tree.  governs  if 1.  is the head of a phrase and a potential governor 2. A phrase headed by  dominates  3. There does not exist a g such at g governs  and  governs g Potential governors All lexical categories: N, V, A, P Head of finite clauses

Binding Theory (Revised): 

Binding Theory (Revised) The governing category of  is the minimal phrase that contains , the governor of , and a subject (a NP at spec of an IP or a NP) that c-commands the governor. Binding Theory Principle A: A NP with [+anaphor] must be bound within its governing category. Principle B: A NP with [+pronominal] must not be bound within its governing category. Principle C: A NP with [-anaphor -pronominal] must not be bound.

Example 1: 

Example 1 John likes himself

Example 2: 

Example 2 Mary likes John’s picture of himself

Example 3: 

Example 3 *John wanted Mary to take a picture of himself

Example 4: 

Example 4 John considers himself to be the best

Example 5: 

Example 5 John said that pictures of himself were on sale

Example 6: 

Example 6 *Mary believes herself can afford the car

Binding and PRO: 

Binding and PRO PRO is treated like lexical NPs John persuaded Maryi PROi to defend herself/*himself Johni promised Mary PROi to defend himself/*herself

Problem Cases: 

Problem Cases They knew/found that each other’s photos were on sale Mary believes it is possible for herself to win Jill knew that nothing could obliterate the memory of those photographs of herself [Napoli93] Ralph considers Mary inferior to himself [Napoli93, p.519] ?Ralph considers John inferior to himself

Local Domain (Revisted Again): 

Local Domain (Revisted Again) The Local Domain of  is the minimal phrase that contains  , its governor, and a subject (a NP at spec of an IP or a NP) that c-commands the governor and is accessible to .

Non-referential NPs: 

Non-referential NPs Some NPs, such as nothing, there, it (expletive), are not accessible to anything.

Each Other’s: 

Each Other’s “Each other’s” is not accessible to “each other’s”

A Singular Nouns is not Accessible to “Each Other”: 

A Singular Nouns is not Accessible to “Each Other” Pollard&Sag 94, p.245 John and Mary know that the journal had rejected each other’s papers Why are John and Mary letting the honey drip on each other’s feet [Chomsky 1973: 261] John suggested that tiny gilt-framed portraits of each other would make ideal gifts for the twins The agreement that Iran and Iraq reached guaranteed each other’s trading rights in the disputed waters until the year 2010

Inaccessibility between Argumentsof a Predicate: 

Inaccessibility between Arguments of a Predicate If two arguments of a predicate are known to be distinct a priori, they are not accessible to each other. Ralph considers Mary inferior to himself [Napoli93, p.519] *Ralph considers Mary fond of himself [Napoli93, p.519]

Accessibility: 

Accessibility A is inaccessible to B if, disregarding agreement features, A could not possibly bind B. Otherwise, A is accessible to B

Exceptions to Principle B: 

Exceptions to Principle B Example Jill took her brother with her to the market [Napoli93,513] The use of “her” instead of “herself” may be explained by Full Interpretation “X took Y with Z” implies Z=X. the only purpose to use an anaphor as Z is to indicate Z=X

Exceptions to Principle C: 

Exceptions to Principle C ABC applauded the new contract, which gave the network more flexibility. The company said it plans to use the sale proceeds to invest in business opportunities more closely identified with the company’s “refocused direction.”

Anaphors without Governing Category: 

Anaphors without Governing Category Not all anaphors have governing categories: A letter from Mary about herself was in the mail [Kuno93, p.138] Those nude pictures of himself ruined John’s career. [Napoli93, p550] Revised Principle A: If an anaphor has a governing category, it must be bound within its governing category. If an anaphor has no governing category, it must be co-indexed with the most accessible NP in the context.

Examples of Anaphor without GC: 

The picture of himselfi in Newsweek bothered Johni *The picture of himselfi in Newsweek bothered John’si father The picture of himselfi in Newsweek dominated John’si thoughts The picture of himselfi in Newsweek shattered the piece of mind that Johni had spent the last six months trying to restore. Examples of Anaphor without GC

Conclusion: 

Conclusion We proposed a definition of Governing Category that is simpler and has better empirical coverage than Chomsky’s earlier definition.

Unresolved Problems: 

Unresolved Problems John made sure it was clear to Mary that the picture of himself was already sold Mary made sure it was clear to John that the picture of himself was already sold Bill suspected the silence meant that a picture of himself would soon be on the post office wall [Pollard&Sag94, p.268]

Problems with C-command: 

Problems with C-command Pollard&Sag94 pointed out the following problems Mary talked to John about himself *Mary talked to himi about Johni Possible solution redefine c-command so that prepositions do not block c-command introduce linear order requirement in c-command