Anaphora 1

1
Local anaphora
When Mr. Smith arrived, she was drunk.
Mr. Smith ? she disagreement
When Ms. Smith arrived, she was drunk.
Ms. Smith she preferred in isolation Ms.
Smith ? she possible in context
When she arrived, Ms. Smith was drunk.
she ? Ms. Smith preferred she Ms. Smith
weakly possible
2
Local anaphora (2)
Mr. Smith said that he will leave.
Mr. Smith ? he or Mr. Smith he
He said that Mr. Smith will leave.
he ? Mr. Smith he c-commands Mr. Smith
A non-pronominal, non-reflexive NP cannot corefer
with an NP that c-commands it.
3
Local anaphora (3)
Mr. Smith thought that the man was sick.
Mr. Smith ? the man the c-command criterion
Mr. Smith thought that he was sick.
Mr. Smith ? he or Mr. Smith he
4
Local anaphora (4)
Ms. Smith saw her in the mirror.
Ms. Smith ? her non-reflexivity
Ms. Smith saw herself in the mirror.
A reflexive pronoun must refer to a c-commanding
NP in the same local domain. The local domain of
a constituent C is the set of all constituents in
the nearest S or NP above C.
5
Non-local anaphora
We need local discourse contexta few sentences
back are usually enough.
Mr. Smith lost his keys.He looked for them
everywhere.
Agreement plays a role here.
Mr. Smith lost his keys.Mr. Brown did too.
"Did too" refers to a VP.
continued
6
Non-local anaphora (2)
Mr. Smith lost his keys.He looked for them
everywhere.Mr. Brown did too.
This works in the absence of conjunctions.
Mr. Smith lost his keys,so he broke the
lock.Mr. Brown did too. (?)
continued
7
Non-local anaphora (3)
Mr. Smith lost his keysand missed the bus.Mr.
Brown did too.
Mr. Smith lost his keyswhen he missed the
bus.Mr. Brown did too.
8
Non-local anaphora (4)
We need a list of discourse entities possible
antecedents or co-referents.

• an indefinite NP (usually introduces a new
  entity)Mr. Smith bought a bottle of wine. It was
  expensive.
• a definite NP or a pronoun (usually a
  reference)Mr. Smith met Mr. Brown. The man was
  frantic.
• a plural NP (a set of objects, with collective or
  distributive reading)He bought two books. They
  were interesting.He bought oranges and potatoes.
  The fruits were fresh.

9
Non-local anaphora (5)
Anaphora resolution based of history lists.

• Identify discourse entities.
• Apply local constraints.Mr. Smith saw Mr. Brown
  yesterday.Mr. Brown gave him a letter.him ? Mr.
  Brown, so maybe him Mr. Smith
• Put some reasonably recently introduced discourse
  entities on the history list.

continued
10
Non-local anaphora (6)

• Go back, try each entity for local constraints
  agreement, reflexivity, c-command maybe
  selectional restrictions.This mean that most
  recent is favoured.
• ExampleMr. Smith drives an expensive car.Mr.
  Brown drives a wreck.He knows that he can
  win.Mr. Brown is preferred.

continued
11
Non-local anaphora (7)

• Preferences within one local contextmajor
  constituents before adjuncts and subordinate
  constituents.Mr. Smith drank the wine on the
  table.It was brown and round. (?)
• Differences between major constituents can be
  quite subtle.Mr. Smith saw Mr. Brown at the
  party.He went to the bar to get a drink.Mr.
  Smith saw Mr. Brown at the party.He clearly had
  too much drink.

12
Non-local anaphora (8)

• Discourse centre (focus) once established, it
  dominates (is preferred).Mr. Smith was late.
  Mr. Smith is in focus.When he arrived, Mr.
  Brown met him.He decided to leave early.
• Precedencesubject gt object gt indirect object gt
  others.One of them will be the preferred next
  centre Cp Cb is the actual, backward-looking
  centre.

continued
13
Non-local anaphora (9)

• Constraints.
• If there is a pronoun, the centre must also be a
  pronoun.
• The centre is the most preferred entity that a
  pronoun refers to.
• Changing the centre is usually not favoured.
• These and other constraints can be used to
  generate a ranked list of antecedents for a
  pronoun (with Cb gt Cp gt others), and to designate
  a new centre (it can be old, or really new if
  there is no pronoun).

continued
14
Non-local anaphora (10)
1 While Mr. Smith was walking in the park, he
met Mr. Brown. 2 He invited him to the
party. if Cb Mr. Smith Cp. 1' While Mr.
Smith was walking in the park, he met Mr.
Brown. 2' He invited him to the party. if Cb
Mr. Smith, Cp Mr. Brown.
15
Definite descriptionsand world knowledge
She bought a book and a magazine.The book was
overpriced. He looked at the moon. She walked up
to the garden and opened the gate. A possible
recognition procedurelook through the local
context for exactly one object that fits the
description of the noun phrase. This, naturally,
assumes a fairly accurate knowledge
representation schema.
continued
16
Definite descriptions and world knowledge (2)
For complex NPs, such as "the car in the garage",
we must get both entities imagine car1 in
garage1, car2 in the yard and an empty garage2. A
few more subtle examples There was a school
raffle. The winner got a vase. Jack took out a
pencil. The lead was broken. And just a taste of
anaphora with sets Jim, Mary and Pete went
shopping. The boys got beer. Jim took two bikes
along. He mostly rode the BMX.
17
Discourse analysis
A Okay, we're done with the speakers. S1 Just
connect them to the tuner. S2 By the way, got
batteries for the clock? S3 B Yeah, brought some
today. S4 A Were they on sale? S5 B Uhm, and I
got more so I could have them for my walkman and
the smoke detector. S6 A Okay. S7 Have you
connected them? S8
S3-S6 is a separate subdialogue. It opens with
"By the way". S7 closes it with "Okay".
18
Discourse analysis (2)
We need to segment the dialogue. This is based on
cue phrases. The structure is well represented by
a stack. We need a few restricting assumptions

• A fixed set of dialogue participants
• A simple temporal progression of events
• Well-defined goals of the participant (if
  possible)

19
Discourse analysis (3)
Another type of discourse is a story with
subplots and communicative goals.
Event Comm. Goal Jack shopped
early. E1 introduce E1 He took the
car E2 elaborate E1 and bought six
lobsters. E3 elaborate E1 When he returned
home, E4 pick up after E1 he began to cook
dinner. E5 pick up after E4
E1 includes E2, E1 includes E3, E2 precedes
E3,E4 precedes E5, E4 enables E5
20
Discourse analysis (4)
If there is no relationship (as between S2 and
S3), we can take it as a signal of a new
topic. To represent a segment, we need to know
the state of the discourse the
sentences, the local context, coherence
relations between sentences. This information can
also sit on a stack.
21
Discourse analysis (5)
Examples of cue phrases Structural cues by the
way start digression anyway end
digression bye end dialogue first, next,
last introduce a subtopic now introduce a
subtopic okay close a subtopic
continued
22
Discourse analysis (6)
Semantic cues and continuation because causation,
reason but, however contrast furthermore new
subtopic meanwhile new topic so,
thus conclusion then causal, temporal therefore su
mmary
23
Discourse analysis (7)
More cues Support the parent segment by... in
particular specifics in addition extras in
general generalization for example illustration "P
arallel" cues on the one hand, on the other
hand in contrast similarly
24
Discourse analysis (8)
Segments have a discourse purpose an unclear
but intuitive idea. The specifics depend on the
overall goal of the discourse. In describing a
complex entity, segments are arranged to mirror
the structure. In describing a complex event, the
arrangement may mirror the temporal sequence. In
a debate, one makes claims that interact
segments might reflect that.