ESSLLI 2007 19th European Summer School in Logic, Language and Information August 6-17, 2007 http://www.cs.tcd.ie/esslli2007 Trinity College Dublin Ireland C OURSE R EADER ESSLLI is the Annual Summer School of FoLLI, The Association for Logic, Language and Information http://www.folli.org Metonymy. Reading Materials (III) for the ESSLLI-07 course on Figurative Language Processing Birte Lönneker-Rodman July 1, 2007 1 1.1 What is Metonymy? Introduction This definition follows (Kövecses, 2002, pp. 143–144). In metonymy one entity, or thing (such as Shakespeare, Pearl Harbor, Washington, glove in Examples 1 to 4), is used to indicate [. . . ] another entity. One kind of entity “stands for” another kind of entity. (1) I’m reading Shakespeare. (2) America doesn’t want another Pearl Harbor. (3) Washington is negotiating with Moscow. (4) We need a better glove at third base. Exercise/Question: What might be the entities indicated? Can we find literal paraphrases for these sentences? The metonymically used word refers to an entity that provides mental access to another entity (the one we refer to in the literal paraphrase). For this to be possible, the entities must be related to one another. Particular, systematically exploited relations give rise to larger groups or clusters of metonymic expressions, in which members of particular classes of entities stand for members of particular other classes of entities. These will be discussed in Section 1.2 under the lable of “regular metonymy”. Terminology. The entity that “stands for” another one can be called the vehicle entity. The vehicle is thus the entity that provides mental access to the other entity. The entity that becomes accessible (or: to which mental 1 access is provided) is called target entity; (cf. Kövecses, 2002, p. 145). This can be represented by the following pattern: (5) vehicle-entity for target-entity A target entity, being an individual or instance, should not be confused with a target domain as in metaphorical mappings, which is a class or concept, or rather a bundle of related classes and concepts (Metaphor chapter!). As opposed to source and target domain in metaphor, vehicle and target entity in a given metonymic expression are closely related to each other. The relation underlying the metonymy is based on the “closeness” or contiguity or vehicle and target entity in conceptual space. We will easily find out why the entities in the examples mentioned above are “close” to each other: What do they have to do with each other? Rather than belonging to different conceptual domains, metonymically related entities are members of the same domain. For example, both an author and written works belong to the (artistic) production domain, containing the producer, the product, the place where the product is made, etc. The coherence of such a domain is thought to be brought about and ensured by the repeated co-occurrence of such entities in the world, were we experience them as being (closely) “together”. (Kövecses, 2002, pp. 145–146) As with metaphorical mappings, though, some relations between some types of entities tend to entail wide-spread, regular metonymic patterns (whereas there are also many relations between many entities that are rarely or never exploited for metonymy). 1.2 Regular metonymy as a form of regular polysemy The regularity of some of the metonymic patterns has been noted by Apresjan (1973) and Nunberg (1995) (under the label of “systematic polysemy”), among others. Examples of these regular patterns can also be found in (Lakoff and Johnson, 1980, pp. 38-39). In what follows, small capitals will be used to indicate classes of entities, or concepts. Therefore, the headlines are all in small capitals. the part for the whole (6) We don’t hire longhairs. (7) The Giants need a stronger arm in right field. object used for user 2 (8) The sax has the flu today. (9) The gun he hired wanted fifty grand. (10) The buses are on strike. (11) [flight attendant, on a plane]: Ask seat 19 whether he wants to swap. (Nissim and Markert, 2003, p. 56) the place for the event (12) Let’s not let Thailand become another Vietnam. (13) Watergate changed our politics. Other commonly mentioned regular metonymies include the tree for the wood: The table is made of oak, cf. Nunberg (1995). There are cross-linguistic differences as to which regular metonymies are available, cf. Nunberg (1995). Some, especially those involving place names and other proper names, seem to be very wide-spread among different languages, though. Exercise/Question: Is the fruit for the tree a regularly exploited metonymic pattern in your language? As far as country names as vehicle entities are concerned, an English corpus study (Markert and Nissim, 2003) reveals that three coarse-grained mapping patterns account for most of the metonymies encountered (Nissim and Markert, 2003, p. 57): 1. place for people subsuming different subtypes; 2. place for event 3. place for product. See Section 2 below for further details on this and other corpus studies. – In spite of the possible grouping of metonymies into clusters, which presumably facilitates their understanding, a correct and detailed interpretation of metonymies always requires the activation of world knowledge. For example, the reader has to figure out to which target entity the entity mentioned by the metonymic label is related (e.g., long hair and arms are parts of persons) or which function the user of a used object is assumed to fulfil (e.g. player or the sax, killer (using the gun), driver (but not passenger) of the bus, passenger currently occupying a numbered seat). Probably because of the relative unpredictability of the function of the user, (Nissim and Markert, 2003, p. 57) call (Example 11) “unconventional”. 3 1.3 Two senses per context? When annotating a corpus for possibly metonymic place names, Markert and Nissim (2003) found examples where two predicates are involved, triggering a different reading each, thus yielding a “mixed” reading. This occurs especially often with coordinations and appositions. (14) . . . they arrived in Nigeria, hitherto a leading critic of the South African regime . . . (Nissim and Markert, 2003, p. 57) Example 14 invokes both a literal reading of Nigeria (triggered by “arriving in”) and a place-for-people reading (triggered by “leading critic”). Similarly complex cases have been discussed by Nunberg (1995) (Examples 15 to 17): (15) Yeats did not like to hear himself read in an English accent. (Contrast: I am often read in an English accent.) (16) Roth is Jewish and widely read. (17) The newspaper Mary works for was featured in a Madonna video. Nunberg is of the opinion that the target expressions (metonymical vehicles) in these examples do not receive different (double) readings. Rather, he argues, the predicates (i.e., what is “said about” them) have a transferred reading so that they can be applied to the same (identical) entity referred to by the vehicle. This view is not easily compatible with the cognitive linguistic viewpoint presented by Lakoff and Johnson (1980) or Kövecses (2002), who do not discuss these cases. 1.4 How figurative are metonymies? We refer back to the discussion of literal, non-literal and figurative linguistic expressions in the session on Figurative Language. By paraphrasing the metonymic expressions in our examples above with cognitively similarly simple expressions, we have proven that the additional naming criterion is fulfilled for metonymies. To decide whether they are also figurative, we must investigate their image component. For instance, do Examples (1) to (4) above evoke images? Dobrovol’skij and Piirainen (2005) argue that metonymies which participate in regular polysemy do “not evoke any images” and “do not imply any additional prgamatic effects”, but are merely a “powerful and near-universal mechanism for denoting conceptually related entities in a most economical and natural way”. The existence of an image component is only recognized for certain idiom-like metonymies such as (18) or (19). 4 (18) a helping hand (19) to keep an eye on someone/something Whether speakers perceive an image component by consciously evoking the literal meaning of the metonymic expression and combining this with the context, or whether they do not think of the product as an image, is a question that cannot be decided on the basis of linguistic facts alone. It is not excluded that some speakers might perceive an image component, for at least some of the metonymies discussed here. As long as the image component question has not been resolved, it is most safe to treat metonymies in general as non-literal (but non-figurative) language, whereas some speakers might think of some or even all of them as figurative. 2 Metonymy annotation and frequency Country names. Annotating 1,000 occurrences of country names (with a three-sentence context, from the British National Corpus) and labeling them according to eleven categories, Markert and Nissim (2003) achieved an inter-annotator agreement between two annotators of kappa 0.88. The categories are as follows: 1. unsure: context not understandable for annotator, 2. nonapp: country name is part of a larger expression denoting a different named entity, e.g. US Open, 3. homonym: a name from a different semantic class, e.g. person name: Professor Greenland, 4. literal, e.g. em coral coast of Papua New Guinea or Britain’s current account deficit, 5. obj-for-rep: object for representation, e.g. This is Malta. (pointing to a photograph), 6. obj-for-name: object for name, and name used as a mere signifier, e.g. (from organization corpus, see below) Chevrolet is feminine because of its sound (it’s a longer word than Ford, has an open vowel at the end, [. . . ], 7. place-for-event: cf. Example (2) above, 5 8. place-for-people: This is often labeled place for institution in cognitive linguistic reference works, but there are different subclasses (distinguished in the annotation scheme of Markert and Nissim (2003)). Examples include: America did try to ban alcohol and a 29th-minute own goal from San Marino defender Claudio Canti. A country name can indeed also stand for (almost) the entire population of the country, which makes palce for institution too narrow a category; 9. place-for-product: the place for a product manufactured there (e.g. em Bordeaux), 10. othermet: “unconventional metonymies”, cf. Example (11) above, 11. mixed: cf. Subsection 1.3 above. Of the 1000 examples of country names, Markert and Nissim (2003) 61 (6.1%) were excluded as noise (nonapp, homonym), and 14 examples could not be agreed on after discussion (unsure). This results in 925 clearly labeled examples. 737 are literal. Among the remain metonymic ones, the largest subgroup is place-for-people with 161 instances and place-for-event metonymies constitute the smallest group (three members or 0.3% of the entire data). Organization names. Markert and Nissim (2006) report on the annotation efforts mentioned above, as well as on the annotation of organization names. They distinguish between five different subtypes of regular metonymic mappings involving organization names: 1. organisation-for-members: The concrete referents are often underspecified (e.g. spokesperson, certain classes of employees, all members, . . . ). Example: Last February NASA announced [. . . ]. 2. organisation-for-facility, e.g. The opening of a McDonald’s is a major event. 3. organisation-for-product, e.g. press-men hoisted their notebooks and their Kodaks. 4. organisation-for-index, especially for stock index, e.g. Eurotunnel was the most actove stock. 6 5. organization-for-event, especially a particularly bad or otherwise outstanding event associated with the organization, e.g. . . . the resignation of Leon Brittan from Trade and Industry in the aftermath of Westland.1 In addition to these five categories, the labels object-for-name (see above), other and mixed were available for manual annotation of 984 instances of organization names. The largest part of the organization name instances in the corpus were literal (64.3%). Overall inter-annotator agreement for two annotators was found to be kappa 0.894. The highest reliability scores were achieved for object-for-name (6 instances) and organisation-for-facility (14 instances), but also the metonymic category with the most members (organisation-for-members, 188 instances) had a kappa score higher than the overall sample. Kappa was lowest for the more complex class mixed. Markert and Nissim (2003) and Markert and Nissim (2006) point out that kappa values for metonymy annotation are higher in “second runs” on independent data, after a training-and-discussion phase involving annotation on a first example set. 2.1 Availability • The corpora annotated by Markert and Nissim have been made available at http://www.cogsci.ed.ac.uk/∼malvi/mascara/index.html [30 June, 2007]. • A different corpus annotated for some types of metonymy (among other things) is the ACE corpus (http://projects.ldc.upenn.edu/ ace/data/, [30 June, 2007]). The latest version of the annotation guidelines is (LDC, 2005). The annotated data can be obtained from the Linguistic Data Consortium (LDC), but this availability seems to be restricted to sites participating in the ACE project (Automatic Content Extraction). 1 Note that a human reader, even if unaware of the “economic scandal involving the helicopter company Westland in Britain in the 1980s” (Markert and Nissim, 2006), will infer that Westland stands for an event. 7 Figure 1: Similarity levels in regular metonymy. 3 3.1 Metonymy recognition as Word Sense Disambiguation (WSD) Nissim and Markert (2003) A class-based approach is supposed to take advantage of the regularities of metonymic mappings, even if exemplified by different lexical material: [W]hereas a classic (supervised) WSD algorithm is trained on a set of labelled instances of one particular word and assigns word senses to new test instances of the same word, (supervised) metonymy recognition can be trained on a set of labelled instances of different words of one semantic class and assign literal readings and metonymic patterns to new test instances of possibly different words of the same semantic class. (Nissim and Markert, 2003, p. 58) The similarities that follow from the regular mapping are illustrated by Figure 1, taken over from (Nissim and Markert, 2003, p. 57). Nissim and Markert (2003) use a decision list classifier and estimate probabilities via maximum likelihood with smoothing (p. 58). Due to data sparseness, the trained classifier will not be able to make a decision for all cases in the test data, so accuracy and coverage are measured as follows: 8 Accuracy = # correct decisions made # decisions made (1) # decisions made # test data (2) Coverage = When the classifier cannot make a decision, a backoff decision is to assign the most frequent class in the training data, which is literal in this case. Accb is then the accuracy for the entire data, after this backoff method has been applied. After backoff, coverage is always 1.0 or 100%. Precision, recall, and f-measure for metonymies (i.e. for non-literal readings) are also reported. When evaluating the results, a baseline is established by always assigning the most frequent reading (literal) to each example in the test data. Test results are reported on the annotated corpus of 925 clearly labeled examples of country names (cf. Subsection 2 above), using 10-fold crossvalidation. 3.1.1 The basic feature – Algorithm I The feature on which the first and most important decision list classifier is trained is called role-of-head. It is one feature, composed of • the grammatical role (grammatical function) of the possibly metonymic word (target word): active subject, subject of a passive sentence, direct object, modifier in a prenominal genitive, other nominal premodifier, dependent in a prepositional phrase – other functions are summarized under the label “other”; • the lemmatized lexical head of the possibly metonymic word, in a dependency grammar framework. Examples: (20) England won the world cup. Possibly metonymic word: England. Value for role-of-head: subj-of-win (21) Britain has been goverend by [. . . ]. Possibly metonymic word: Britain. Value for role-of-head: subjp-of-govern 9 The feature was manually annotated. On average, target words with grammatical function (GF) subj or subjp were predominantly metonymical, whereas all other GFs were biased towards a literal reading of the target word. After training on the role-of-head feature alone, precision and accuracy were found to be relatively high (accuracy as defined in Equation 1 above: 0.902), but coverage as defined in Equation 2 above was low (0.631). This makes is necessary to resort to backoff (always assign literal) in 36.9% of the cases and results in low recall (0.186) and low F-measure (0.298) for metonymies. Some problems with wrong assignment have been detected. In these cases, the chosen feature is “too simplistic”. Main reasons for wrong assignment are: 1. semantically “empty” lexical heads, such as the verbs be and have, or the preposition with, which can occur in both literal and non-literal contexts (cf. border with Hungary vs. talk with Hungary); 2. ambiguity of the premod relation in noun-noun compounds (cf. US operation: an operation in or by the US?). 3.1.2 Generalization – Algorithm II Low coverage was identified as the main problem of the basic algorithm, and it can be explained by data sparseness: many head words occur only once in the data. Therefore, two methods were used to relax the identity-of-feature criterion, in those cases where a decision could not be made based on the full feature. This means that everything which can be classified by algorithm I remains untouched, and generalization applies only to those examples that would otherwise have been sent to backoff directly. The first generalization method involves generalizing the lexical head to similar words from Lin’s (Lin, 1998) thesaurus of content words sorted by part-of-speech. This allows a generalization from Example (22) to Example (23), in case the feature subj-of-lose had not been seen in training: (22) England won the World Cup. (23) Scotland lost in the semi-final. As soon as a decision can be made based on a similar word, the algorithm stops, which means that less similar words are also less likely to influence on the decision. Nevertheless, up to 50 similar words were examined to find a feature seen in the training data: the more words are examined, the 10 Figure 2: Results without and with generalization over semantically similar lexical heads. better recall and precision of metonymies. For (up to) 50 similar words, the F-measure value is 0.542, recall 0.410 and precision 0.802. Accuracy without backup lowers a little, to 0.877, but accuracy with backup is better than before. The sets dealt with by the different algorithms are visualized in Figure 2. Exercise/Question: What are possible reasons for the increase in (overall) precision, using this generalization method? 3.1.3 Generalization – Algorithm III The second generalization method is to drop head word information altogether and to base the decision on the preference indicated by the feature grammatical function only, for which a separate decision list classifier has been trained. This algorithm thus assigns all target words in subject position to the non-literal group (cf. information on grammatical function in Subsection 3.1.1 above) and performs slightly better than the one using the previous generalization method. 3.1.4 Combination The best choice is to combine the two generalization methods and use GFbased decisions only if the target is a subject, thesaurus-based generalization otherwise. This method yields a precision of 0.814, a recall of 0.510 and an Fmeasure of 0.627. Accuracy of the combined method is 0.894, and accuracy after backup is 0.87. 11 3.1.5 Clean data Remember that the data used for this experiment is very clean. First of all, manual tagging removed all instances of names that were not country names, as well as those whose metonymicity was undecidable for a human. Second, the manual annotation of the training feature ensures high quality of the data. The authors also measured the influence of automatical parsing, on the same data set, and found that it reduces F-measures for non-literal recognition by about 10%, as compared to training on manually annotated features. 3.2 Peirsman (2006) Peirsman (2006) experiments with different approaches to the problem discussed in Nissim and Markert (2003), using the same data set of mixed country names (cf. Subsection 2 above) and an additional (separate) data set for the country name Hungary, as well as the same evaluation methods. He finds out that an unsupervised approach, based on a WSD algorithm proposed by Schütze (1998) and reminding of LSA (Latent Semantic Analysis, (Landauer and Dumais, 1997)), fails to achieve the majority baseline for accuracy. Nevertheless, this unsupervised WSD algorithm does find two clusters that significantly correlate with the manually assigned literal-nonliteral labels (this is measured with the χ2 test). In a different experiment, he includes subcategorization into different classes of metonymical mappings (for the available subclasses, see Subsection 2 on corpus annotation). With grammatical function and lexical head as features (similarly as in Nissim and Markert (2003)), Peirsman (2006) trains a memory-based learning classifier (TiMBL2 ). This achieves an accuracy of 86.6% and an F-score of 0.612 and is thus able to nearly reproduce the best results achieved by Nissim and Markert (2003), i.e. those of their combined generalization algorithm (87.0% accuracy and an F-measure of 0.627). A similar experiment was to enlarge the previous feature set by WordNet hypernym synsets of the head’s first sense. Although semantically differently grained hypernym synsets were experimented with, and even in spite of manual sense disambiguation, this feature did not seem to have a noticeable influence on accuracy. It improved recall and F-score slightly. It is not sure whether this failure to improve accuracy is due to a mismatch between WordNet synsets and the metonymical classes (semantic labels), or to the 2 http://ilk.uvt.nl/software.html [30 June, 2007]. 12 high frequency of function words as lexical heads, or to other unknown factors. 3.3 An adaptation of the approach by Gedigian et al. (2006) In the session on Metaphor, we have discussed a metaphor classification approach for Motion and Cure verbs by Gedigian et al. (2006). This verbcentered approach has recently been applied to metonymy recognition in an experiment by Schneider (2007). For this experiment, verbs were chosen from the FrameNet Statement frame: acknowledge, add, address, admit, etc. A random subset of sentences from the Penn TreeBank containing these verbs was labeled for literal, metonymic, or other3 . Out of 1,600 investigated sentences, 832 were literal and 420 metonymic, which brings the ratio of literal examples among the relevant subset to 0.664. Of special interest is here the Propbank argument ARG0, which labels the speaker for these communication verbs. A (superficial) look at the annotated data reveals (at least the following) different types of metonymy: • organization for members - proper name: Rolls-Royce Motor Cars Inc. said it expects its U.S. sales to remain steady at about 1,200 cars in 1990 . • organization for members or place for people, but no proper name: – [. . . ] the SEC ’s office of disclosure policy , which proposed the changes . – The company said the plan , under review for some time , will protect shareholders [. . . ]. • product for producer/written document for writer (probably in interaction with a metaphor such as writing is verbal communication): Many of the letters maintain that investor confidence has been so shaken [. . . ]. The annotations show biases for some of the verbs. To illustrate, remark, observe and caution were not found to be used with a metonymic speaker in the corpus, whereas the verbs state and address were used predominantly with a metonymic speaker (each in 66% of their occurrences). 3 Including slightly different senses of the verb, e.g. The state agency ’s figures confirm .... 13 Schneider (2007) trained a Maximum Entropy classifier4 on this data, testing different feature sets. Only accuracy measures are reported. The classifier outperforms baseline accuracy (66.4%, achieved by assigning literal throughout) even if trained on the verb as the only feature (accuracy on test set: 78.14%). Not surprisingly, though, the best result of 91.5% accuracy is achieved by using the feature ARG0 Type (semantic head of ARG0). A combination of ARG0 Type with the verb as additional feature yields a slightly lower accuracy (89.46%). Building on the insight that there are relatively few and distinguishable groups of literal and metonymic usages, based on the semantic type of ARG0’s head (see itemized list above), a generalization over the head words was performed. This uses 26 general categories from an expanded version of WordNet (Snow et al., 2006) as “type” of the argument, instead of using the semantic head itself. In this case, hypernymic generalization helped improve accuracy (94.3% on test set). 3.4 Markert and Nissim (2007) Markert and Nissim (2007) report on the recent SemEval-2007 task on Metonymy Resolution, in which five systems participated. 4 Maximum Entropy Modeling Toolkit for Python and C++ by Zhang Le, http: //homepages.inf.ed.ac.uk/s0450736/maxent toolkit.html [30 June, 2007]. The experiment was performed with 100 iterations of the GIS algorithm. 14 4 Answers to the Questions 4.1 From Section 1.1 What might be the entities indicated? Can we find literal paraphrases for these sentences? (Kövecses, 2002, p. 144) proposes: (1’) one of Shakespeare’s works, (2’) defeat in war, (3’) the American government, (4’) baseball player. 4.2 From Section 1.2 Is the fruit for the tree a regularly exploited metonymic pattern in your language? [Examples: lime - the fruit or the tree5 ; but apple?; Examples from German] 4.3 From Section 3.1.2 What are possible reasons for the increase in (overall) precision, using this generalization method? The examples in S2 consist of cases with highly predictive content word heads as (a) function words are not included in the thesaurus and (b) unpredictive content word heads like “have” or “be” are very frequent and normally already covered by hmr (they are therefore members of S1). Precision on S2 is very high (84%) and raises the overall precision on the set S. (Nissim and Markert, 2003, p. 60) Also, generalization deals with a much higher proportion of metonymies than the basic algorithm. Whereas the basic algorithm classifies 583 instances out of which 80 (31.6%) are metonymies, generalization classifies another 147 instances, among which 68 (46%) are metonymies. Cf. Figure 3. 5 a juicy round fruit which is sour like a lemon but smaller and green, or the small Asian tree on which this fruit grows (Cambridge Advanced Learner’s Dictionary, http: //dictionary.cambridge.org/ [1 July, 2007]) 15 Figure 3: Proportions of literal vs. metonymic usages classified (not necessarily correctly). References Apresjan, J. D. (1973). Regular polysemy. Linguistics, 142, 5–32. Dobrovol’skij, D. and Piirainen, E. (2005). Figurative Language: Crosscultural and Cross-linguistic Perspectives. Elsevier. Gedigian, M., Bryant, J., Narayanan, S., and Ciric, B. (2006). Catching metaphors. In Proceedings of the 3rd Workshop on Scalable Natural Language Understanding, pages 41–48, New York City. Kövecses, Z. (2002). Metaphor: a practical introduction. Oxford University Press, New York. 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