CSA405: Advanced Topics in NLP

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CSA405 Advanced Topicsin NLP

• Machine Translation I
• Introduction to MT

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Outline

• MT Machine Translation
• Why MT is important
• What MT is and why MT is difficult
• MT and the Human Translator

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Why Machine Translation is Important
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Implications of Multilinguality
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Commerical Interest

• US has invested in MT for intelligence purposes
• MT is popular on the web - the most ued of
  Google's special features
• EU spends more that 1B per annum on translation

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Academic Interest

• Different NL technologies include
• parsing
• generation
• morphology
• pronoun resolution
• understanding ...

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Misconceptions about MT

• MT is a waste of time because
• you will never make a machine that can translate
  Shakespeare.
• the quality  of translation you can get from an
  MT system is very low
• MT threatens the jobs of translators.
• MT systems are machines, and buying an MT system
  should be very much like buying a car.

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Facts about MT

• There are many situations where the ability to
  produce reliable, if less than perfect,
  translations at high speed is valuable.
• MT systems can take over some of the boring,
  repetitive translation jobs and allow human
  translation to concentrate on more interesting
  specialist tasks.
• Building an MT system is an arduous and time
  consuming job, involving the construction of
  grammars and very large monolingual and bilingual
  dictionaries.

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The Place for MT

• Human Translators are good at
• Getting the right turn of phrase
• Preserving translation equivalence
• Human Translators are bad at
• Dictionary look-up
• Consistency of translation
• Translation of terminology
• MT can exploit these weaknesses

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Summary

• MT is important because
• There are too few human translators
• Availability of materials in appropriate language
  has significant economic consequences.
• Scientifically, it is still one of the best test
  areas for language technology

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Why Translation is Difficult
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What Makes MT Hard

• Style and Meaning
• Word Order
• Word Sense
• Pronouns
• Tense
• Idioms

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Style and Meaning

• As recently as a decade ago it was widely
  believed that infectious disease was no longer
  much of a threat in the developed world. The
  remaining challenges to public health there, it
  was thought, stemmed from noninfectious
  conditions such as cancer, heart disease and
  degenerative diseases.

• Il y a une dizaine dannees, on croyait que les
  pays industrialises etait debarasses des risques
  lies aux maladies infectieuses et que la sante
  publique netait menacee que par des maladies
  comme le cancer, les troubles cardiaques, et les
  anomolies genetiques

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Style and Meaning

• English
• Two sentences
• infectious disease was no longer much of a threat
  in the developed world
• The remaining challenges to public health there
• noninfectious conditions

• French
• One sentence
• les pays industrialises etait debarasses des
  risques lies aux maladies infectieuses
• la sante publique netait menacee que
• maladies

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Different word orders

• English word order is subject - verb - object
• Japanese order is subject - object - verb
• English IBM bought Lotus
• Japanese IBM Lotus bought
• English Reporters said IBM bought Lotus
• Japanese Reporters IBM Lotus bought said

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Word Sense Ambiguity

• Bank as in river
• Bank as in financial insitution
• Plant as in tree
• Plant as in factory
• Different senses usually translate into different
  words

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Hutchins Somers (1992)
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Problems Contextual Interpretation
OPEN
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Different Cultural Models
English Health Insurance German Krankenversiche
rung French Assurance Maladie
English validate French obliterer
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Differences in Marking of Semantic Information

• Head marking.
• In English possessive relation is marked on the
  head The man's house
• In Hungarian it is marked on the dependentThe
  man house-his
• his house / sa maison
• Direction and manner of motion marking
• He ran into the room (English)
• He entered the room running (French)

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Summary

• Translation is about more than equivalence of
  meaning.
• Translation may involve the resolution of
  ambiguity.
• Preservation of intention involves cultural
  background as well as linguistic knowledge.
• Translation is a hard problem for humans let
  alone machines.

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Similarities and Differences Between Languages

• Differences
• Morphology
• Word order and syntactic structures
• Marking of semantic distinctions
• Lexical

• Similarities
• Communicative function for survival
• Mechanisms for reference to people, eating,
  politeness, time.
• Syntactic complexity
• Nouns
• Verbs

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Machine Translation and Human Translators
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In the Beginning ....was the dream of FAMT

• Fully Automatic (High Quality) Machine
  Translation (Bar Hillel 1960)

Source Language text
TargetLanguage text
FAHQMT
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FAMT

• Basic Charactistics
• No human intervention
• Arbitrary text
• Evaluation Criteria
• Quality of ouput
• Cost (/page)
• Speed (pages/hour)

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FAMT Success StoryTAUM METEO

• Written by Chevalier et al. 1978.
• Translation of weather reports from English to
  French
• Highly constrained subset of English
• Small number of senses for each word
• Restricted syntactic constructions
• System determines whether a given sentence is
  within its capabilities
• Very fast, very accurate, no post-editing

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FAMT MORAL

• FAMT can work well but only if we give up one or
  more of the goals e.g.
• Unrestricted text input
• High quality translation
• This observation has lead to research on
  sub-languages
• And to the use of FALQT

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FAMT is not the only way

• FAMT lies at one extreme of a continuum of ways
  in which technology can be brought to bear upon
  the translation problem
• At the other extreme there are word processing
  software, fax machines, and even mobile phones
• Between these two extremes there are other points
  of interest where technology can radically affect
  the productivity of the individual translator.

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MAHT and HAMT

• Machine Aided Human Translation (MAHT)
• Human Aided Machine Translation (HAMT).
• The essential difference between these two lies
  not only in the way in which the person is
  involved but also in the extent of their
  involvement

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MAHT - Translation Memories

• Systems consist of a database in which each
  source sentence of a translation is stored
  together with the target sentence (this is called
  a translation memory "unit")
• Any new source sentences will be searched for in
  the database and a match value is calculated.
• When the match value is 100, the translation of
  the source sentence from the database is inserted
  into the text being translated.

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MAHT - Translation Memories

• If the match value is below 100 and above a
  certain user-definable percentage (i.e., "fuzzy
  match"), the old translation will be inserted as
  a translation proposal for the translator to
  review and edit.
• Sentences with match values below that margin
  have to be translated from scratch.
• New and changed translation proposals will then
  be stored in the database for future use.

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MAHT - Translation Memories Advantages

• Avoid redoing translation of repeated material
• Use previous texts as a model for new
  translations
• Ensure consistency throughout a translation

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MAHT - Translation Memories - Drawbacks

• If terminology changes between projects the
  content of a TM needs to be updated to reflect
  these changes.
• Blind faith in exact matches (without validation)
  can generate incorrect translation since there is
  no verification of the context where the new
  segment is used compared to where the original
  one was used.

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MAHT - Translation Memories - Remarks

• Translation Process TM tools may not easily fit
  into existing translation or localization
  processes work best where work can be signed off
  in pieces rather than as a whole.
• Customisation rarely works straight out of the
  box. Menu adaptation, filters to desktop
  applications may require significant effort.
• Investment costs are high
• Setup and maintenance of TMs has to factored in.
• OpenTag/TMX formats for exchanging TM data
  between competing systems

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MAHT Other Technology

• Communication/coordination amongst translators
• Integration of internet technologies and web
  services.
• Database technology, smart indexing, and
  networking
• Improvements can be achieved that are well within
  the scope of current technology.

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HAMT Human Assisted Machine Translation

• Machine retains the initiative but works in
  collaboration with human consultant.
• System translates autonomously until it
  recognises that a linguistic difficulty of a
  certain type has arisen, e.g.
• ambiguity
• pronoun reference
• unknown word
• unrecognised construction
• At this point it seeks help from the consultant.

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HAMT Challenges

• Reliable identification/classification of
  difficulty.
• Reliable communication of difficulty to user.
• Tradeoff between quality and scope of
  translation.

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HAMT - Advantages

• Modulo challenges a high quality of translation
  can be guaranteed.
• Speed if large sections of text can be
  translated automatically.
• Human consultant need not necessarily have all
  the skills of a human translator native
  competence in one or both languages may suffice.

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Summary

• Machine Translation is a continuum
• FAMT
• HAMT
• MAHT
• The utility of a given type of system cannot be
  assessed with very simple criteria
• Utlility function involves at least the human
  cost, the machine cost, the quality of the
  result, and the nature of the translation
  requirements.

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Some References

• Jonathan Slocum, Machine Translation its
  History, Current Status, and Future Prospects,
  Proc ACL 1984, Stanford University,
  http//acl.ldc.upenn.edu/P/P84/P84-1116.pdf
• Martin Kay Machine Translation, Computational
  Linguistics vol 11 numbers 2-3 1985.
• Richard Kittredge Sublanguages, Computational
  Linguistics vol 11 numbers 2-3 1985.