A Computational Account of Some Constraints on Language

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A Computational Account of Some Constraints on
Language

• Mitchell Marcus
• MIT Artificial intelligence Laboratory
• Presented by Mi-young KANG

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Introduction (1/2)

• This paper
• outlines two constraints,
• Subjacency Principle (SP)
• Specified Subject Constraint (SSC)
• fall out naturally from the structure
  "Determinism Hypothesis.
• shows that the structure of the grammar
  interpreter (PARCIFAL) constrains parsing process
  in such a way that, grammar rules cannot parse
  sentences which violate either the SP or SSC.

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Introduction (2/2)

• "Determinism Hypothesis" claims, in the course of
  the parsing process,
• Natural language can be parsed by simple
  mechanism without using backtracking.
• Once built, no grammatical structure can be
  discarded or altered.

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Structure of the Grammar Interpreter (I/3)

• Two major data structures of PARCIFAL
• Active node stack
• Incomplete constituents
• Three-place constituent buffer
• Complete constituents whose higher level
  grammatical function is yet uncertain

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Structure of the Grammar Interpreter (2/3)

• The parser has the following operations
• create a new node at the bottom of the active
  node stack.
• attach the constituents in the buffer to the new
  node.
• drop the top node in the parse stack into the
  buffer.

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Structure of the Grammar Interpreter (3/3)

• Grammar is made up of pattern/action rules.
• a pattern
• Subset of constituents of the buffer
  Accessible nodes in the active node stack
• an action
• a sequence of operations which acts on these
  constituents).
• Each rule is assigned a numerical priority.
• Rule packet (pattern/action rules) is activated
• by associating that packet with the constituent
  at the bottom of the active node stack.
• General forme of grammar rule
• Rule ltnamegt priority ltpriority) in ltpacketgt
• ltpatterngt --gt ltactiongt
• Ex)
• RULE START-AUX PRIORITY 10. IN PARSE-AUX
• v e r b --gtCreate a new aux node.

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General Grammar Framework -trace- (1/2)

• Trace
• Phonologically null" NP in the surface structure
  representation of a sentence.
• has no daughters but is "bound" to the NP that
  filled that position at some level of underlying
  structure.
• Pointer to that NP.

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General Grammar Framework -trace- (2/2)

• Wh-head of a question or relative clause
• Passivized clause
• Embedded clause

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Passive sentence (1/2)

• Parallel analysis of simple declarative.
• One exception the rule PASSIVE-AUX in packet
  BUILD-AUX

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Passive sentence (2/2)

• The packet SUBJ-VERB contains the rule PASSIVE
• The action of the rule PASSIVE
• creates a trace.
• bindes the trace to the subject of the dominating
  S node.
• drops the new trace into the buffer.
• Two rules activate (V17)
• OBJECTS in packet SS-VP
• INF-S-START1 in packet INF-COMP

• used in pattern descriptions, is read as
  has the feature(s).
• C (or c ) the current active node (i.e. the
  bottom of the stack)

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Raising

• PASSIVE rule drops the trace it creates into the
  buffer rather than immediately attaching the new
  trace to the VP node,
• In order to correctly analyze passives which
  involve "raising with no additional complexity
  added to the grammar.

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Simple Passive and Raising (1/4)

• Two traces
• The subject of the embedded clause, is bound to
  the subject of the major clause.
• The object of the embedded S, is bound to the
  first trace.

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Simple Passive and Raising (2/4)
The meeting was believed to have been scheduled
forWednesday.

• AUX node has been labelled passive
• The packet SUBJ-VERB is active.
• PASSIVE rule contained in this packet(SUBJ-VERB)
  matches and is executed.

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Simple Passive and Raising (3/4)
The meeting was believed to have been scheduled
forWednesday.

• activate the packet SS-VP (which contains the
  rule OBJECTS)
• "believe" takes infinitive complements, the
  packet INF-COMP (which contains INF-S-START1),
• ?
• The patterns of OBJECTS and INF-S- START1 will
  both match
• INF-S-START1(slide 11) is executed because it has
  priority.

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Simple Passive and Raising (4/4)
The meeting was believed to have been scheduled
forWednesday.
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The Specified Subject Constraint (1/3)

• No rule may involve two constituents that are
  Dominated by different cyclic nodes unless the
  lower of the two is the subject of an S or NP.
• No rule may involve constituents X and Y, if a
  and ß are cyclic nodes and Z is the subject of a,
  Z distinct from X.

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The Specified Subject Constraint (2/3)

• The rule "MOVE NP"
• free to shift any NP into the empty subject
  position,
• constrained by the SSC so that the object of the
  embedded S cannot be moved out of that clause.

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The Specified Subject Constraint (3/3)

• If a trace is "lowered" from one clause to
  another as a result of a "MOVE NP"during the
  parsing process, then it will be attached as the
  subject of the second clause.

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Subjacency (1/3)

• No rule can involve constituents that are
  separated by more than one Cyclic node.

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Subjacency (2/3)

• (a) must derived by a movement operation that
  results in a structure analogous to (c) or (d),
• each of these movements leaving a trace.
• (f) is ruled out because it violate Subjacency.

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Subjacency (3/3) Lowering a trace more than 1
clause

• (1) A trace NP1 must
• be created with S1, as the current S
• bound to some NP Dominated by that S
• dropped into the buffer.
• (2) S2 must be created, spplanting S1 as the
  current S,
• (3) S3 must he created, becoming the current S.
• The trace NP1 remains sitting in the buffer
  during all these steps,
• By the Specified Subject Constraint,
• NP1 must then attach to S3 as its subject.