Sunday, December 2, 2007
Machine translation, sometimes referred to by the acronym MT, is a sub-field of computational linguistics that investigates the use of computer software to translate text or speech from one natural language to another. At its basic level, MT performs simple substitution of words in one natural language for words in another. Using corpus techniques, more complex translations may be attempted, allowing for better handling of differences in linguistic typology, phrase recognition, and translation of idioms, as well as the isolation of anomalies.
Current machine translation software often allows for customisation by domain or profession (such as weather reports) — improving output by limiting the scope of allowable substitutions. This technique is particularly effective in domains where formal or formulaic language is used. It follows then that machine translation of government and legal documents more readily produces usable output than conversation or less standardised text.
Improved output quality can also be achieved by human intervention: for example, some systems are able to translate more accurately if the user has unambiguously identified which words in the text are names. With the assistance of these techniques, MT has proven useful as a tool to assist human translators, and in some cases can even produce output that can be used "as is". However, current systems are unable to produce output of the same quality as a human translator, particularly where the text to be translated uses casual language.
The translation process may be stated as:
Decoding the meaning of the source text; and
Re-encoding this meaning in the target language.
Behind this ostensibly simple procedure lies a complex cognitive operation. To decode the meaning of the source text in its entirety, the translator must interpret and analyse all the features of the text, a process that requires in-depth knowledge of the grammar, semantics, syntax, idioms, etc., of the source language, as well as the culture of its speakers. The translator needs the same in-depth knowledge to re-encode the meaning in the target language.
Therein lies the challenge in machine translation: how to program a computer that will "understand" a text as a person does, and that will "create" a new text in the target language that "sounds" as if it has been written by a person.
This problem may be approached in a number of ways.
Pyramid showing comparative depths of intermediary representation, interlingual machine translation at the peak, followed by transfer-based, then direct translation.
Machine translation can use a method based on linguistic rules, which means that words will be translated in a linguistic way — the most suitable (orally speaking) words of the target language will replace the ones in the source language.
It is often argued that the success of machine translation requires the problem of natural language understanding to be solved first.
Generally, rule-based methods parse a text, usually creating an intermediary, symbolic representation, from which the text in the target language is generated. According to the nature of the intermediary representation, an approach is described as interlingual machine translation or transfer-based machine translation. These methods require extensive lexicons with morphological, syntactic, and semantic information, and large sets of rules.
Given enough data, machine translation programs often work well enough for a native speaker of one language to get the approximate meaning of what is written by the other native speaker. The difficulty is getting enough data of the right kind to support the particular method. For example, the large multilingual corpus of data needed for statistical methods to work is not necessary for the grammar-based methods. But then, the grammar methods need a skilled linguist to carefully design the grammar that they use.
To translate between closely related languages, a technique referred to as shallow-transfer machine translation may be used.
Main article: Dictionary-based machine translation
Machine translation can use a method based on dictionary entries, which means that the words will be translated as a dictionary does — word by word, usually without much correlation of meaning between them.
Main article: Statistical machine translation
Statistical machine translation tries to generate translations using statistical methods based on bilingual text corpora, such as the Canadian Hansard corpus, the English-French record of the Canadian parliament and EUROPARL, the record of the European Parliament. Where such corpora are available, impressive results can be achieved translating texts of a similar kind, but such corpora are still very rare. The first statistical machine translation software was CANDIDE from IBM. Google used SYSTRAN for several years, but has switched to a statistical translation method in October 2007. Recently, they improved their translation capabilities by inputting approximately 200 billion words from United Nations materials to train their system. Accuracy of the translation has improved. 
Main article: Example-based machine translation
Example-based machine translation (EBMT) approach is often characterised by its use of a bilingual corpus as its main knowledge base, at run-time. It is essentially a translation by analogy and can be viewed as an implementation of case-based reasoning approach of machine learning.
Main article: Interlingual machine translation
Interlingual machine translation is one instance of rule-based machine-translation approaches. In this approach, the source language, i.e. the text to be translated, is transformed into an interlingual, i.e. source-/target-language-independent representation. The target language is then generated out of the interlingua.
 Major issues
Main article: Word sense disambiguation
Word sense disambiguation concerns finding a suitable translation when a word can have more than one meaning. The problem was first raised in the 1950s by Yehoshua Bar-Hillel . He pointed out that without a "universal encyclopedia", a machine would never be able to distinguish between the two meanings of a word . Today there are numerous approaches designed to overcome this problem. They can be approximately divided into "shallow" approaches and "deep" approaches.
Shallow approaches assume no knowledge of the text. They simply apply statistical methods to the words surrounding the ambiguous word. Deep approaches presume a comprehensive knowledge of the word. So far, shallow approaches have been more successful.
 Named entities
Related to named entity recognition in information extraction.
Main article: History of machine translation
The history of machine translation begins in the 1950s, after World War II. The Georgetown experiment (1954) involved fully-automatic translation of over sixty Russian sentences into English. The experiment was a great success and ushered in an era of substantial funding for machine-translation research. The authors claimed that within three to five years, machine translation would be a solved problem.
Real progress was much slower, however, and after the ALPAC report (1966), which found that the ten-year-long research had failed to fulfill expectations, funding was greatly reduced. Beginning in the late 1980s, as computational power increased and became less expensive, more interest was shown in statistical models for machine translation.
There are now many software programs for translating natural language, several of them online, such as the SYSTRAN system which powers both Google translate and AltaVista's Babel Fish. Although no system provides the holy grail of "fully automatic high quality machine translation" (FAHQMT), many systems produce reasonable output.
Despite their inherent limitations, MT programs are used around the world. Probably the largest institutional user is the European Commission, which employs a highly-customised version of the commercial SYSTRAN MT system to automatically translate a large volume of document preliminary drafts for internal use.
Global Translations, a translation agency in the USA, has been developing specialized dictionaries for machine translation of tenders for telecommunications companies. Due to the highly technical nature of these documents, which are often very large in volume, machine translation quality improves dramatically in proportion to the text corpus that is imported into the dictionaries.
A Danish translation agency, Lingtech A/S , has been translating patent applications from English to Danish since 1993, using a proprietary rule-based machine-translation system, PaTrans , working together with the commercial translation-memory-based Trados CAT tool.
The Spanish daily newspaper Periódico de Catalunya is translated from Spanish into Catalan with an MT system .
Toggletext uses a transfer-based system (known as Kataku) to translate between English and Indonesian.
Google has claimed that promising results were obtained using a proprietary statistical machine translation engine . The statistical translation engine used in the Google language tools for Arabic <-> English and Chinese <-> English has an overall score of 0.4281 over the runner-up IBM's BLEU-4 score of 0.3954 (Summer 2006) in tests conducted by the National Institute for Standards and Technology.    Uwe Muegge has implemented a demo website  that uses a controlled language in combination with the Google tool to produce fully automatic, high-quality machine translations of his English, German, and French web sites.
With the recent focus on terrorism, the military sources in the United States have been investing significant amounts of money in natural language engineering. In-Q-Tel  (a venture capital fund, largely funded by the US Intelligence Community, to stimulate new technologies through private sector entrepreneurs) brought up companies like Language Weaver. Currently the military community is interested in translation and processing of languages like Arabic, Pashto, and Dari. Information Processing Technology Office in DARPA hosts programs like TIDES and Babylon Translator. US Air Force has awarded a $1 million contract to develop a language translation technology. 
Main article: Evaluation of machine translation
There are various means for evaluating the performance of machine-translation systems. The oldest is the use of human judges to assess a translation's quality. More recent, automated means of evaluation include BLEU, NIST and METEOR.
Relying exclusively on machine translation ignores that communication in human language is context-embedded, and that it takes a human to adequately comprehend the context of the original text. Even purely human-generated translations are prone to error. Therefore, to ensure that a machine-generated translation will be of publishable quality and useful to a human, it must be reviewed and edited by a human.
It has, however, been asserted that in certain applications, e.g. product descriptions written in a controlled language, a dictionary-based machine translation system has, in a production environment, produced perfect translation results that require no human intervention. 
 See also
Comparison of Machine translation applications
Controlled natural language
History of machine translation
Human Language Technology
List of research laboratories for machine translation
^ Milestones in machine translation - No.6: Bar-Hillel and the nonfeasibility of FAHQT by John Hutchins
^ Bar-Hillel (1960), "Automatic Translation of Languages". Available online at http://www.mt-archive.info/Bar-Hillel-1960.pdf
^ Informe sobre el sistema de traducción automática del Periódico de Catalunya (in Spanish)
^ Google Blog: The machines do the translating (by Franz Och)
^ Geer, David, "Statistical Translation Gains Respect", pp. 18 - 21, IEEE Computer, October 2005
^ Ratcliff, Evan "Me Translate Pretty One Day", Wired December 2006
^ "NIST 2006 Machine Translation Evaluation Official Results", November 1, 2006
^ This demo website uses a controlled language in combination with the Google engine
^ GCN — Air force wants to build a universal translator
^ Muegge (2006), "Fully Automatic High Quality Machine Translation of Restricted Text: A Case Study," in Translating and the computer 28. Proceedings of the twenty-eighth international conference on translating and the computer, 16-17 November 2006, London, London: Aslib. ISBN 978-0-85142-483-5.
Hutchins, W. John; and Harold L. Somers (1992). An Introduction to Machine Translation. London: Academic Press. ISBN 0-12-362830-X.
 External links
At Wikiversity, you can learn about:
International Association for Machine Translation (IAMT)
Machine Translation, an introductory guide to MT by D.J.Arnold et al. (1994)
Machine Translation Archive by John Hutchins. An electronic repository (and bibliography) of articles, books and papers in the field of machine translation and computer-based translation technology
Machine translation (computer-based translation) — Publications by John Hutchins (includes PDFs of several books on machine translation)
NIST Machine Translation Tests - index
Machine Translation and Minority Languages
John Hutchins 1999
Retrieved from "http://en.wikipedia.org/wiki/Machine_translation"
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