LING 406 Intro to Computational Linguistics Computational Morphology and Morphological Theory

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LING 406Intro to Computational
LinguisticsComputational Morphologyand
Morphological Theory

• Richard Sproat
• URL http//catarina.ai.uiuc.edu/L406_08/

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This Lecture

• Overview of a thriving debate in morphological
  theory
• and its computational interpretation

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Item-and-arrangement versus Item and process

• Charles Hockett (1954) Two models of grammatical
  description
• Item-and-arrangement words are composed of
  morphemes that are put together by a kind of
  word syntax
• Item-and-process words are built up via the
  application of rules that add phonological and
  morphosyntactic information

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For example

• The word dogs
• An item-and-arrangement analysis
• dogN sN__, pl gt dogsN, pl
• Each morpheme carries its meaning and syntactic
  properties with it, and
• An item-and-process analysis
• Ø gt s / N, pl __

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The separation hypothesis(Beard, 1995 Beard
Volpe, 2005)

• Lexical and inflectional derivation are processes
  distinct from phonological realization
  (affixation, etc.).
• Again theres a clear difference between Item
  and Process and Item and Arrangement theories

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Stumps classification
hoots3sg
Øs / hoot3sg
hoots 3sg because of -s
-s is introduced due to 3sg
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Turkish (Hankamer, 1986)
çöplüklerimizdekilerdenmiydi garbageAFF
PL 1P/PL LOC REL PL ABL
INT AUXPST was it from those that
were in our garbage cans?
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Kannada
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Reduplication
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Problems for IA

• Multiple exponence
• Breton
• bagig little boat
• bagoùigoù little boats
• Classical Greek
• pepaideuka I have educated

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Problems for IA

• Zero exponence Russian feminine nouns

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But is there really a difference?

• Suppose we reduce both item and arrangement and
  item and process to a computational
  interpretation?
• Is there any difference between the two?

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An alternative view

• In (Roark Sproat, 2006) we reanalyze Stumps
  analyses of
• Sanskrit nominal declensions
• Swahili verbal declensions
• Breton double plurals
• All of which purport to show the need for an
  realizational-inferential account

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Sanskrit declensions
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Sanskrit declensions
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Issues with Sanskrit

• Nouns have two or three stems strong, middle
  and (optionally) weakest
• A different series of stem alternations
  cross-cuts this guna, vrddhi, and zero
• foot pad-, pad-, pd-
• strong stems may be guna or vrddhi
• middle stems may be zero, or a lexeme-specific
  stem
• weakest stems may be zero or lexeme-specific stem

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Sanskrit declensions
zero
guna
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Sanskrit declensions
vrddhi
lexeme-class particular
lexeme-class particular
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Further issues

• Stump argues for Indexing Autonomy Hypothesis
• A stems index is independent of the form used
  for the stem
• Sanskrit nominal declensions are morphomic in
  Aronoffs sense
• Also involved are rules of referral whereby a
  particular form is systematically used to
  represent more than one slot in the paradigm.
• For example, in Latin the ablative and dative
  plural in nominal paradigms are identical no
  matter what form is used for the particular
  paradigm
• So we have several layers of complexity here,
  which would seem to make an item-and-arrangement
  approach impossible

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Computational analysis
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Refactoring
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A simpler example from (Blevins, 2003)

• Verbal d in West Germanic
• PAST John whacked the toadstool
• PERF John has whacked the toadstool
• PASS The toadstool was whacked
• Lexical-incremental accounts posit three
  homophonous affixes
• Blevins proposes a realization function

Affixes /d/ to the stem
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Refactorization
This is simply an incremental-lexical model
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English agentive nominals (cf. Beard Volpe,
2005)

• read-er, stand-ee, correspond-ent, record-ist,
  cook
• e " ent / entnoun,agentive S __
• Call the set of all agentive rules R
• We can define a new metarule R' that is the
  union of all rules in R

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Feature noun,agentive

• Presumably this is also introduced by rule call
  this rule M
• Then given a base B, the base with that feature
  specification added is given by B?M
• Then the appropriate suffixed form is given by
  B?M?R'
• But this can be written, by associativity, as
  B?M?R'
• Finally, M?R' can be precomposed call this R''
  

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So what?

• R''
• Introduces the morphosyntactic feature
  noun,agentive
• Introduces the affixal morphology as appropriate
  to the base
• In short, R'' encodes a lexical-incremental model
  of morphology.

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Why form-function mismatch?

• Affixes frequently show a non-one-to-oneness
  between form and function this is rarely if ever
  true of lexemes
• Still, for cases like the English agentive, part
  of the explanation must surely be historical.
• E.g., -ent, is associated with Latinate stems,
  which either were used as agentives originally,
  or became so via lexical drift
• Is something beyond such a historical story
  required?

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Summary

• Morphological theory has been divided between
  item-and-process and item-and-arrangement
  approaches
• Yet when viewed from a formal or computational
  point of view there is relatively little
  difference between these two approaches
• This again echoes Karttunens point about the
  non-difference between traditional rule-based
  approaches to phonology and constraint-based
  approaches.

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Reading

• RS Ch. 3 - 4