Coreference Strategies in E nglish- G erman Translation (2020)

Abstract: We present a study focusing on variation of coreferential devices in English original TED talks and news texts and their German translations. Using exploratory techniques we contemplate a diverse set of coreference devices as features which we assume indicate language-specific and register-based variation as well as potential translation strategies. Our findings reflect differences on both dimensions with stronger variation along the lines of register than between languages. By exposing interactions between text type and cross-linguistic variation, they can also inform multilingual NLP applications, especially machine translation.

## introduction coreference devices and their usage vary both across and within languages depending on several factors such as register and style among others. moreover, translation process evokes a number of translation phenomena, such as explicitation or interference @xcite that also have an impact on the choice of linguistic expressions used. we assume that variation in coreference devices depends on the following factors: (a) language-specific constraints, (b) functional variation across language registers as well as (spoken or written) mode and (c) effects of the translation process. translating between languages involves transformation of the source coreference patterns into the target ones. analysing such patterns can give insights into translation strategies for referring expressions in texts. variation along the above stated lines (a, b, c) causes a number of problems in multilingual coreference resolution or coreference annotation projection @xcite @xcite . although several studies describe such problems @xcite @xcite , there is still a lack of understanding as to which linguistic phenomena and concretely, which structures cause these problems. in this paper, we attempt to detect such phenomena for english-german translations in a data set containing two different text registers: ted talks, which represent spoken language, and news, a type of written discourse. previous studies show that the choice of referring expressions depends on the mode of text production in both languages under analysis @xcite . the phenomena we analyse are not restricted to expressions referring to simple, nominal antecedents, but also comprise expressions referring to events. we also include cases of comparative reference, substitution and ellipsis, which according to @xcite trigger a type reference relation (and not the relation of identity), or "sloppy identity". our main goal is to shed light on cross-lingual differences in coreference expressions. another goal is to explore possible translation strategies for the language pair under analysis and the given text types. for this, we perform an empirical, corpus-based analysis using a number of coreference features as indicators of cross-lingual variation. the features are extracted from an existing corpus annotated with coreference chains. they include morpho-syntactic and functional properties of referring expressions, as well as chain properties. using correspondence analysis and hierarchical cluster analysis we detect specific features of coreference distinctive for the two dimensions (language contrast and register variation) under analysis. our results show that both language and register (or mode) give rise to differences in our data and the coreference features vary depending on the dimensions. knowledge on the differences in the realisation of the coreference phenomena depending on the language or register is valuable to cross-lingual coreference resolution, as it was already acknowledged in the community, e.g. the conll-2012 shared task on coreference resolution included multiple languages, registers and modes within ontonotes @xcite . knowledge of the analysed variation is even more important for contrastive linguistics and (machine) translation. ## related work several studies in the area of translation have addressed the importance of coreference @xcite @xcite . however, these works are example-based and provide neither a comprehensive account, nor empirical evidence for their claims. there are a few corpus-based studies of coreference translation @xcite @xcite , addressing mostly the challenge of translating pronouns. the awareness of this challenge has also increased in the mt community @xcite @xcite @xcite @xcite , and its relevance for multilingual coreference resolution is beyond doubt @xcite @xcite . still, coreference translation is affected by many factors and remains poorly understood. @xcite analyse coreference and other means of explicit discourse phenomena in english and german comparable texts. they find that english and german differ in the linguistic means available in their language systems to convey coreference. english provides less syntactic flexibility and is restricted in the distribution of referents. german has more options and tends to use more grammatical means of coreference than english @xcite , which indicates that english and german differ in how coreference chains are built up in terms of form and type of referring expressions within the chains. @xcite base their analyses on the assumptions within contrastive pragmatics @xcite suggesting that meanings are expressed more explicitly by linguistic signals in german than in english. however, @xcite claim that translation strategies cannot rely on knowledge about contrastive lexico-grammar alone -awareness of preferred patterns that distinguish the languages and registers are essential for translators. the authors state that translating coreference chains from english into german implies using a higher number of coreferring expressions, and at the same time, chains of two elements may drop out because of remetaphorisation (i.e. change in word class). the authors use comparable corpora of original texts in both languages for their analyses, which does not provide them with the insights of what is actually happening in translation in the given language pair. their findings include recommendations for translation strategies, but not the observation of the translation behaviour. @xcite focus on cohesive devices in english and german original (spoken and written) texts and report a higher degree of cohesiveness in german than in english, while overall spoken texts show more cohesive devices than written texts. @xcite analyse incongruences in the annotation of nominal coreference in english-german translations. the majority of the discovered incongruences are caused by explicitation -german translations contain more explicit linguistic devices triggering coreference. they point out that these cases of explicitation do not necessarily arise from the translation process, but can also be caused by idiosyncrasies of the two languages in terms of coreference properties. however, while looking into parallel chains, the authors do not provide analyses of the differences in the type of referring expressions in the source and the target texts. moreover, their analysis is restricted to nominal coreference only. based on the previous literature, we can assume that the german translations contain more referring expressions and more chains than the english source texts. conversely, shorter chains should be more common in the english originals than in the german translations. in terms of the structure and function of coreference chain members, there should be more explicit linguistic devices expressing coreference in the translations. in particular, translations would prefer demonstrative forms instead of personal reference, and entity reference instead of events (with entity reference being more concrete). in addition to such differences between originals and translations, we also expect variation in terms of register or mode, which may occasionally be even more prominent than that between languages @xcite . ## analysed features in our analyses, we use a number of coreference features that are related to the form, functional and structural properties of chain members, as well as chain properties. first of all, we are driven by the structures available in the annotated corpus at hand. the morpho-syntactic and functional subtypes of anaphors and cataphors (which we collectively refer to as referring expressions) are motivated by the analyses by @xcite , who grades various types of referring expressions according to their degree of explicitness. this is important for our analyses, as our data contains translations, and explicitation -a higher explicitness of linguistic means in translated texts -is a well-known effect of the translation process. the levels of explicitness of referring expressions are related to @xcite 's concept of accessibility. morpho-syntactic types of referring expressions are related not only to accessibility, but also to the givenness or salience of a referent in the recipient's mind @xcite @xcite . in studies involving register or genre variation, the distribution of morpho-syntactic types of mentions, such as the prevalence of pronouns vs. nouns, also plays an important role @xcite @xcite . morpho-syntactic subtypes of referring expressions, substitution and ellipsis, as well as the scope of antecedents were analysed by @xcite and @xcite to reveal differences between registers and between the languages english and german. the scope of coreference is reflected in the differentiation between reference to entities vs. events, and in the form of the antecedent (nominal, verbal, clausal). as referring expressions can have more than one antecedent, the distinction between split and simple antecedent is also important. the resolution of anaphors with multiple antecedents differs in its processing from the resolution of single anaphors @xcite . the accessibility of a referent is also related to certain chain properties @xcite : a high degree of accessibility is related to low distance between anaphors in long coreference chains and a low overall number of different coreference chains. the distance between anaphors and their antecedents is an important metric in many coreference resolution systems. distance can be measured in different ways. the distance measure used in this work is the number of intervening sentence boundaries. this metric was also used by @xcite for coreference resolution in czech and by @xcite for the analysis of variation in spoken and written texts. in this study we include the following categories to analyse variation in the english-german coreference chains (a more detailed description is contained in ## results we first perform a correspondence analysis with all the features described in section 3 above to get a general overview of how features are distributed along the lines of text types or languages. the resulting two-dimensional graph is shown in figure 1 . a detailed output of all the three ca analyses with the information on feature weights, contribution to eigenvalues, their distance to the centroid, etc. is given in tables 3 , 4 , 5 in appendix. the most obvious information we can obtain from this is that variance is most strongly pronounced between the two registers, while language contrast only marginally seems to play a role. the registers vary along dimension 1 (x-axis) explaining a very high portion (84.6%) of the variation, while languages vary along dimension 2 (y-axis) explaining only 14% of variance. the outcome is not surprising, since on the one hand, feature distribution is strongly connected to register types, on the other hand, language contrast is expected to be weaker in translations due to shining through effects (i.e original text structures are kept in the target texts). in the next step, we perform clustering of features -an unsupervised analysis to explore groups of features that arise in our data. we hope that the resulting feature groups will help us to find specific features responsible for the observed register or language contrasts. the cluster analysis (figure 2 ) shows that there are two clear cut groups of features. a closer look at the distributions of the features reveals that the smaller group of features consists of the nine more general and also most common features in all subcorpora, while the other group is much more diverse including more fine-grained features, which are also less common. next, we perform a correspondence analysis on the two groups of features that resulted from hca, starting with the smaller group (figure 3 ). we find that the biggest part of the variation is explained by dimension 1 (x-axis, 71.3%) indicating a strong variance between the registers. the language contrast, i.e. the difference between originals and translations is seen in the second dimension (y-axis). although its contribution is small (explaining 28.5% variation in the data), it is twice as big as the contribution to dimension 2 in figure 1 above, showing that this first feature group reveals more differences between originals and translations than the whole group of features. the features that especially contribute to language contrast are two-member chains and personal pronouns. looking at the first dimension, en news is the most distinct subcorpus, least associated with the selected features with only very weak associations with simple and entity antecedents. in the de news texts we see a moderate association with nps as referring expressions. this is most likely due to the high number of nominal references to a human antecedent (i.e. simone biles, die turnerin, die 19jährige amerikanische turnerin, die amerikanerin, biles, dieses mädchen, der 19-jährigen.). short, two-member chains are most strongly associated with the translated ted talks (de-ted), as well as nps as antecedents. these two features suggest that in the de-ted translations, two member chains with an np antecedent are relatively common. it is possible that some of these short chains are instances where in english there is no chain at all, for instance due to a reduced relative clause as in example (1), or other implicit references in the source text made explicit in the target text. figure 3: ca for all subcorpora with the first group of features resulting from hca (1) a. everybody talks about happiness these days. i had somebody count the number of books with "happiness" in the title published in the last five years [...]. b. jeder spricht heutzutage über das glück. ich habe einige leute die anzahl [der bücher] zählen lassen, [die] mit "happiness" im titel in den letzten fünf jahren veröffentlicht wurden [...]. two-member chains might therefore not indicate a general tendency towards shorter chains in the german translations but rather be an indicator of explicitations of cases where the original keeps the reference implicit. the en-ted talks show a strong association with personal pronouns, indicating frequent pronominal reference. pronominal reference hints at a relatively low level of formality @xcite . the frequent use of personal pronouns in ted talks points to recurring reference to persons as the topic of the talks, see example (2) for illustration. the second group of features shows an even stronger variation along dimension 1 (x-axes), explaining 86.2% of the variation between the two registers (see figure 4 ). figure 4 : ca for all subcorpora with the second group of features resulting from hca here, the language contrast, i.e. the difference between originals and translations is much less prominent. this indicates that the groups we detected by clustering vary in their explaining power for language contrast. while the first group explained 28% of variation between the languages, the second group explains only half of that (12.3%). the second group rather seems to represent distinctiveness between the registers. news texts are highly distinct from ted talks on this graph. responsible features for their distinctiveness are mdn.chain.lngth and stddv.chain.lngth indicating a strong variation in chain length. also the feature lngst.chain is associated with news in both languages, reflecting the fact that news texts often deal with one topic that is focused throughout the whole text. appositions are associated with de-news as well as de-ted talks. appositions can represent explicitations, as in example (3), further defining a referent. the en-news texts are most strongly associated with bare nps and features related to chain length and distance. bare nps in english are, besides plural indefinites, mostly names. their strong association reflects the fact that the en-news texts tend to reiterate the names while german texts tend to reformulate and substitute proper names. in news texts the distance between mentions in a chain seems to be very long, which is especially not problematic for cohesiveness if the referent is reiterated. the en-ted talks show the strongest association with verbal ellipsis (see example ( 4 )) and substitution. these are cohesive devices which represent implicit and "sloppy" ways of creating coreference and are therefore susceptible to explicitation by a translator. the same holds true for comparative reference (np.cm.part, pp.cmp.gen) as well associated with en-ted talks. for extratextual reference we find a moderate association with en-ted talks. plausibly so, since ted talks are video talks where speakers often point at visualization material (presentations, pictures, videos or even other people present on the stage). extratextual reference is often not retained in the target texts, since deictic reference is especially hard to match in subtitles, see example ( 5 ). the same mechanism seems to be at work with the feature "no explicit antecedent", even more strongly associated with the en-ted talks. in cases, where a cue to a possible extratextual referent cannot be found in the text material, the annotator has the option of labelling a referring expression "no explicit". the german translators frequently avoid reference to undefined antecedents leaving them out altogether as illustrated in example ( 6 ). the de-ted talk translations are most strongly associated with generic and indefinite nps. on the german translation side these distinctive features may be results of explicitation attempts, inserting a generic noun where in the english source texts there is no explicit antecedent. also relative clauses distinctive for de-ted texts are typical cases of explicitation. while english offers the option of a reduced variant (in object relative clauses), as well as participle (-ing and -ed clauses), in german, these options do not exist. since ted talks often deal with more complex, scientific topics where a sound understanding by the listener/reader is essential, the feature is found more strongly related to the ted talks than to the news texts. regarding this second group of features, the ted talks differ more from each other than the news texts. one plausible explanation might be the fact that the originally spoken texts through translation are turned into more written-like texts, which is reflected by the distinctive features respectively in the two languages. ## conclusion in the present paper, we explored a number of coreference features in english-german translations that contain texts belonging to two registers. the results show that there is more variation in terms of registers or modes (spoken vs. written) than of languages, which means that english originals and their german translations differ to a lesser extent than news texts and ted talks. this confirms findings of other studies, e.g. @xcite who show that variation along the dimension of mode is more prominent than that along the dimension of language. the authors show this using a set of comparable texts, whereas our data contains originals and their translations, i.e. the same texts in two languages. by using cluster analysis we found two clusters of the features at hand, showing that the more general features represent language contrast better, while a more fine-grained classification of feature categories reflects the register or mode variation. this finding indicates that more general features reveal the differences between originals and translations, whereas a more fine-grained classification of feature categories reflects the register or mode variation. however, we were not able to discover features that would strongly indicate concrete differences between the original and the translated texts, which was one of our original goals. in our future work, we plan to integrate further techniques, such as feature selection technique, e.g. information gain, as used by @xcite to see which features are more informative to predict the two languages in the analysed data. furthermore, it would be interesting to extend our analyses to the other translation direction and see if we observe the same translationese phenomena for the german-english translations. another extension of the work would be adding translations of the same texts into further languages.