Multiword expression
Encyclopedia
A multiword expression is a lexeme
made up of a sequence of two or more lexemes that has properties that are not predictable from the properties of the individual lexemes or their normal mode of combination.
For a shorter definition, MWEs can be described as "idiosyncratic interpretations that cross word boundaries (or spaces)". (Sag et al., 2002: 2).
A multiword expression can be a compound
, a fragment of a sentence, or a sentence. The group of lexemes which makup up a MWE can be continuous or discontinuous. It is not always possible to mark a MWE with a part of speech.
A MWE may be more or less frozen.
Example#1 in English: to kick the bucket
, which means to die rather than to hit a bucket with one's foot. In this example, that is an endocentric
compound, the part of speech may be determined as being a verb
. The MWE is frozen, in the sense that no variation is possible.
Example#2 in English: to throw to the lions . The pattern restricts the usage. The expression is half-frozen because a certain degree of variation is possible but everything is not possible. It is not possible for instance to say to the three lions. Like the previous example, the part of speech is a verb
.
Example#3 in French: la moutarde monte au nez . This MWE is more frozen than the other examples. Let us add that a tense variation is allowed for the verb
but we cannot determine what is the part of speech for the whole expression because it is a sentence.
The number of MWEs in a speaker's lexicon is estimated to be of the same order of magnitude as the number of single words. Specialized domain vocabulary overwhelmingly consists of MWEs, hence, the proportion of MWEs will rise as a system adds vocabulary for new domains, because each domain adds more MWEs than simplex words.
For example, it is hard to predict for a system that an expression like kick the bucket has a meaning that is totally unrelated to the meaning of kick, the and bucket while appearing to conform the grammar of English Vps. Idioms cannot be translated literally, because in many cases the idiom does not exist in an eqivalent form in the target language. Attention has to paid to syntactic and/or semantic (non)equivalence.
Also, not every MWE of the source language has a MWE in the target language as well. For example, the German MWE ins Auge fassen can only be translated by the English one-word term envisage.
For rule based MT it would be to difficult to define rules to translate MWEs, due to the magnitude of different kinds of MWEs.
Nevertheless, an example based MT system has to apply different rules for the translation of continuous and discontinuous MWEs as it is harder to identify a discontinuous MWE in a sentence where words are inserted between the different components of one MWE.
Lexeme
A lexeme is an abstract unit of morphological analysis in linguistics, that roughly corresponds to a set of forms taken by a single word. For example, in the English language, run, runs, ran and running are forms of the same lexeme, conventionally written as RUN...
made up of a sequence of two or more lexemes that has properties that are not predictable from the properties of the individual lexemes or their normal mode of combination.
For a shorter definition, MWEs can be described as "idiosyncratic interpretations that cross word boundaries (or spaces)". (Sag et al., 2002: 2).
A multiword expression can be a compound
Compound (linguistics)
In linguistics, a compound is a lexeme that consists of more than one stem. Compounding or composition is the word formation that creates compound lexemes...
, a fragment of a sentence, or a sentence. The group of lexemes which makup up a MWE can be continuous or discontinuous. It is not always possible to mark a MWE with a part of speech.
A MWE may be more or less frozen.
Example#1 in English: to kick the bucket
Kick the bucket
To kick the bucket is an English idiom that is defined as "to die" in the Dictionary of the Vulgar Tongue . It is considered a euphemistic, informal, or slang term. Its origin remains unclear, though there have been several theories.-Origin theories:...
, which means to die rather than to hit a bucket with one's foot. In this example, that is an endocentric
Endocentric
In linguistics, an endocentric construction is a grammatical construction that fulfills the same linguistic function as one of its parts. An endocentric construction is not an exocentric construction, and an exocentric construction is not an endocentric construction...
compound, the part of speech may be determined as being a verb
Verb
A verb, from the Latin verbum meaning word, is a word that in syntax conveys an action , or a state of being . In the usual description of English, the basic form, with or without the particle to, is the infinitive...
. The MWE is frozen, in the sense that no variation is possible.
Example#2 in English: to throw
Verb
A verb, from the Latin verbum meaning word, is a word that in syntax conveys an action , or a state of being . In the usual description of English, the basic form, with or without the particle to, is the infinitive...
.
Example#3 in French: la moutarde
Verb
A verb, from the Latin verbum meaning word, is a word that in syntax conveys an action , or a state of being . In the usual description of English, the basic form, with or without the particle to, is the infinitive...
but we cannot determine what is the part of speech for the whole expression because it is a sentence.
Machine Translation (MT) of Multiword Expressions
According to Sag et al. (2002) Multiword Expressions are, apart from Disambiguation, one of the two key problems for Natural Language Processing (NLP) and especially for machine translation (MT).The number of MWEs in a speaker's lexicon is estimated to be of the same order of magnitude as the number of single words. Specialized domain vocabulary overwhelmingly consists of MWEs, hence, the proportion of MWEs will rise as a system adds vocabulary for new domains, because each domain adds more MWEs than simplex words.
Problems
The greatest problem for translating MWEs might be the idiomaticity problem, as many MWEs have an idiomatic sense, to a higher or a lesser degree.For example, it is hard to predict for a system that an expression like kick the bucket has a meaning that is totally unrelated to the meaning of kick, the and bucket while appearing to conform the grammar of English Vps. Idioms cannot be translated literally, because in many cases the idiom does not exist in an eqivalent form in the target language. Attention has to paid to syntactic and/or semantic (non)equivalence.
Also, not every MWE of the source language has a MWE in the target language as well. For example, the German MWE ins Auge fassen can only be translated by the English one-word term envisage.
Approaches
The most promising approach to the challenge of translating MWEs is example based MT, because in this case each MWE can be listed as an example with its translation equivalent in the target language.For rule based MT it would be to difficult to define rules to translate MWEs, due to the magnitude of different kinds of MWEs.
Nevertheless, an example based MT system has to apply different rules for the translation of continuous and discontinuous MWEs as it is harder to identify a discontinuous MWE in a sentence where words are inserted between the different components of one MWE.
External links
- Multiword Expression Project, at Stanford UniversityStanford UniversityThe Leland Stanford Junior University, commonly referred to as Stanford University or Stanford, is a private research university on an campus located near Palo Alto, California. It is situated in the northwestern Santa Clara Valley on the San Francisco Peninsula, approximately northwest of San...
- Workshops on Multiword Expressions
- Multiword Expressions in ACL Wiki