{ "paper_id": "P12-1008", "header": { "generated_with": "S2ORC 1.0.0", "date_generated": "2023-01-19T09:28:50.242137Z" }, "title": "PDTB-style Discourse Annotation of Chinese Text", "authors": [ { "first": "Yuping", "middle": [], "last": "Zhou", "suffix": "", "affiliation": { "laboratory": "", "institution": "Brandeis University Waltham", "location": { "postCode": "02452", "region": "MA" } }, "email": "yzhou@brandeis.edu" }, { "first": "Nianwen", "middle": [], "last": "Xue", "suffix": "", "affiliation": {}, "email": "xuen@brandeis.edu" } ], "year": "", "venue": null, "identifiers": {}, "abstract": "We describe a discourse annotation scheme for Chinese and report on the preliminary results. Our scheme, inspired by the Penn Discourse TreeBank (PDTB), adopts the lexically grounded approach; at the same time, it makes adaptations based on the linguistic and statistical characteristics of Chinese text. Annotation results show that these adaptations work well in practice. Our scheme, taken together with other PDTB-style schemes (e.g. for English, Turkish, Hindi, and Czech), affords a broader perspective on how the generalized lexically grounded approach can flesh itself out in the context of cross-linguistic annotation of discourse relations.", "pdf_parse": { "paper_id": "P12-1008", "_pdf_hash": "", "abstract": [ { "text": "We describe a discourse annotation scheme for Chinese and report on the preliminary results. Our scheme, inspired by the Penn Discourse TreeBank (PDTB), adopts the lexically grounded approach; at the same time, it makes adaptations based on the linguistic and statistical characteristics of Chinese text. Annotation results show that these adaptations work well in practice. Our scheme, taken together with other PDTB-style schemes (e.g. for English, Turkish, Hindi, and Czech), affords a broader perspective on how the generalized lexically grounded approach can flesh itself out in the context of cross-linguistic annotation of discourse relations.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Abstract", "sec_num": null } ], "body_text": [ { "text": "In the realm of discourse annotation, the Penn Discourse TreeBank (PDTB) (Prasad et al., 2008) separates itself by adopting a lexically grounded approach: Discourse relations are lexically anchored by discourse connectives (e.g., because, but, therefore), which are viewed as predicates that take abstract objects such as propositions, events and states as their arguments. In the absence of explicit discourse connectives, the PDTB asks the annotator to fill in a discourse connective that best describes the discourse relation between these two sentences, instead of selecting from an inventory of predefined discourse relations. By keeping the discourse annotation lexically grounded even in the case of implicit discourse relations, the PDTB appeals to the annotator's judgment at an intuitive level. This is in contrast with an approach in which the set of discourse relations are pre-determined by linguistic experts and the role of the annotator is just to select from those choices (Mann and Thompson, 1988; Carlson et al., 2003) . This lexically grounded approach led to consistent and reliable discourse annotation, a feat that is generally hard to achieve for discourse annotation. The PDTB team reported interannotator agreement in the lower 90% for explicit discourse relations (Miltsakaki et al., 2004) .", "cite_spans": [ { "start": 73, "end": 94, "text": "(Prasad et al., 2008)", "ref_id": "BIBREF3" }, { "start": 990, "end": 1015, "text": "(Mann and Thompson, 1988;", "ref_id": "BIBREF1" }, { "start": 1016, "end": 1037, "text": "Carlson et al., 2003)", "ref_id": "BIBREF0" }, { "start": 1291, "end": 1316, "text": "(Miltsakaki et al., 2004)", "ref_id": "BIBREF2" } ], "ref_spans": [], "eq_spans": [], "section": "Introduction", "sec_num": "1" }, { "text": "In this paper we describe a discourse annotation scheme for Chinese that adopts this lexically grounded approach while making adaptations when warranted by the linguistic and statistical properties of Chinese text. This scheme is shown to be practical and effective in the annotation experiment.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Introduction", "sec_num": "1" }, { "text": "The rest of the paper is organized as follows: In Section 2, we review the key aspects of the PDTB annotation scheme under discussion in this paper. In Section 3, we first show that some key features of Chinese make adaptations necessary in Section 3.1, and then in Section 3.2, we present our systematic adaptations that follow from the differences outlined in Section 3.1. In Section 4, we present the preliminary annotation results we have so far. And finally in Section 5, we conclude the paper.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Introduction", "sec_num": "1" }, { "text": "As mentioned in the introduction, discourse relation is viewed as a predication with two arguments in the framework of the PDTB. To characterize the predication, the PDTB annotates its argument structure and sense. Two types of discourse relation are distinguished in the annotation: explicit and implicit.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "The PDTB annotation scheme", "sec_num": "2" }, { "text": "Although their annotation is carried out separately, it conforms to the same paradigm of a discourse connective with two arguments. In what follows, we highlight the key points that will be under discussion in the following sections. To get a more comprehensive and detailed picture of the PDTB scheme, see the PDTB 2.0 annotation manual (Prasad et al., 2007) .", "cite_spans": [ { "start": 338, "end": 359, "text": "(Prasad et al., 2007)", "ref_id": "BIBREF3" } ], "ref_spans": [], "eq_spans": [], "section": "The PDTB annotation scheme", "sec_num": "2" }, { "text": "Explicit discourse relations are those anchored by explicit discourse connectives in text. Explicit connectives are drawn from three grammatical classes:", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Annotation of explicit discourse relations", "sec_num": "2.1" }, { "text": "\u2022 Subordinating conjunctions: e.g., because, when, since, although; \u2022 Coordinating conjunctions: e.g., and, or, nor;", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Annotation of explicit discourse relations", "sec_num": "2.1" }, { "text": "\u2022 Discourse adverbials: e.g., however, otherwise, then, as a result, for example.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Annotation of explicit discourse relations", "sec_num": "2.1" }, { "text": "Not all uses of these lexical items are considered to function as a discourse connective. For example, coordinating conjunctions appearing in VP coordinations, such as \"and\" in (1), are not annotated as discourse connectives.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Annotation of explicit discourse relations", "sec_num": "2.1" }, { "text": "(1) More common chrysotile fibers are curly and are more easily rejected by the body, Dr. Mossman explained.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Annotation of explicit discourse relations", "sec_num": "2.1" }, { "text": "The text spans of the two arguments of a discourse connective are marked up. The two arguments, Arg1 and Arg2, are defined based on the physical location of the connective: Arg2 is the argument expressed by the clause syntactically bound to the connective, and Arg1 is the other argument. There are no restrictions on how many clauses can be included in the text span for an argument other than the Minimality Principle: Only as many clauses and/or sentences should be included in an argument selection as are minimally required and sufficient for the interpretation of the relation.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Annotation of explicit discourse relations", "sec_num": "2.1" }, { "text": "In the case of implicit discourse relations, annotators are asked to insert a discourse connective that best conveys the implicit relation; when no such connective expression is appropriate, the implicit relation is further distinguished as the following three subtypes:", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Annotation of implicit discourse relations", "sec_num": "2.2" }, { "text": "\u2022 AltLex: when insertion of a connective leads to redundancy due to the presence of an alternatively lexicalized expression, as in (2). \u2022 EntRel: when the only relation between the two arguments is that they describe different aspects of the same entity, as in (3). \u2022 NoRel: when neither a lexicalized discourse relation nor entity-based coherence is present. It is to be noted that at least some of the \"NoRel\" cases are due to the adjacency constraint (see below for more detail).", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Annotation of implicit discourse relations", "sec_num": "2.2" }, { "text": "(2) And she further stunned her listeners by revealing her secret garden design method: [ Arg1 Commissioning a friend to spend five or six thousand dollars . . . on books that I ultimately cut up.] [ Arg2 AltLex After that, the layout had been easy.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Annotation of implicit discourse relations", "sec_num": "2.2" }, { "text": "(3 ", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Annotation of implicit discourse relations", "sec_num": "2.2" }, { "text": "Discourse connectives, whether originally present in the data in the case of explicit relations, or filled in by annotators in the case of implicit relations, along with text spans marked as \"AltLex\", are annotated with respect to their senses. There are three levels in the sense hierarchy:", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Annotation of senses", "sec_num": "2.3" }, { "text": "\u2022 Class: There are four major semantic classes:", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Annotation of senses", "sec_num": "2.3" }, { "text": "TEMPORAL, CONTINGENCY, COMPARISON, and EXPANSION; \u2022 Type: A second level of types is further defined for each semantic class. For example, under the class CONTINGENCY, there are two types: \"Cause\" (relating two situations in a direct cause-effect relation) and \"Condition\" (relating a hypothetical situation with its (possible) consequences); 1 \u2022 Subtype: A third level of subtypes is defined for some, but not all, types. For instance, under the type \"CONTINGENCY:Cause\", there are two subtypes: \"reason\" (for cases like because and since) and \"result\" (for cases like so and as a result).", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Annotation of senses", "sec_num": "2.3" }, { "text": "It is worth noting that a type of implicit relation, namely those labeled as \"EntRel\", is not part of the sense hierarchy since it has no explicit counterpart.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Annotation of senses", "sec_num": "2.3" }, { "text": "3 Adapted scheme for Chinese", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Annotation of senses", "sec_num": "2.3" }, { "text": "Despite similarities in discourse features between Chinese and English (Xue, 2005) , there are differences that have a significant impact on how discourse relations could be best annotated. These differences can be illustrated with (5):", "cite_spans": [ { "start": 71, "end": 82, "text": "(Xue, 2005)", "ref_id": "BIBREF5" } ], "ref_spans": [], "eq_spans": [], "section": "Key characteristics of Chinese text", "sec_num": "3.1" }, { "text": "(5) \u636e\u6089 according to reports \uff0c , [ AO1 \u4e1c\u839e Dongguan \u6d77\u5173 Customs \u5171 in total \u63a5\u53d7 accept \u4f01\u4e1a company \u5408\u540c contract \u5907\u6848 record \u516b\u5343\u56db\u767e\u591a 8400 plus \u4efd ] CLASS \uff0c[ AO2 , \u6bd4 compare \u8bd5\u70b9 pilot \u524d before \u7565 slight \u6709 EXIST \u4e0a\u5347 ] increase \uff0c , [ AO3 \u4f01\u4e1a company 1", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Key characteristics of Chinese text", "sec_num": "3.1" }, { "text": "There is another dimension to this level, i.e. literal or pragmatic use. If this dimension is taken into account, there could be said to be four types: \"Cause\", \"Pragmatic Cause\", \"Condition\", and \"Pragmatic Condition\". For details, see Prasad et al. (2007) . This sentence reports on how a pilot program worked in Dongguan City. Because all that is said is about the pilot program, it is perfectly natural to include it all in a single sentence in Chinese. Intuitively though, there are two different aspects of how the pilot program worked: the number of records and the response from the affected companies. To report the same facts in English, it is more natural to break them down into two sentences or two semicolon-separated clauses, but in Chinese, not only are they merely separated by comma, but also there is no connective relating them.", "cite_spans": [ { "start": 237, "end": 257, "text": "Prasad et al. (2007)", "ref_id": "BIBREF3" } ], "ref_spans": [], "eq_spans": [], "section": "Key characteristics of Chinese text", "sec_num": "3.1" }, { "text": "This difference in writing style necessitates rethinking of the annotation scheme. If we apply the PDTB scheme to the English translation, regardless of whether the two pieces of facts are expressed in two sentences or two semi-colon-separated clauses, at least one discourse relation will be annotated, relating these two text units. In contrast, if we apply the same scheme to the Chinese sentence, no discourse relation will be picked out because this is just one comma-separated sentence with no explicit discourse connectives in it. In other words, the discourse relation within the Chinese sentence, which would be captured in its English counterpart following the PDTB procedure, would be lost when annotating Chinese. Such loss is not a sporadic occurrence but rather a very prevalent one since it is associated with the customary writing style of Chinese. To ensure a reasonable level of coverage, we need to consider comma-delimited intra-sentential implicit relations when annotating Chinese text.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "\u53cd\u5e94", "sec_num": null }, { "text": "There are some complications associated with this move. One of them is that it introduces into discourse annotation considerable ambiguity associated with the comma. For example, the first instance of comma in (5), immediately following \"\u636e \u6089\" (\"according to reports\"), clearly does not indicate a discourse relation, so it needs to be spelt out in the guidelines how to exclude such cases of comma as discourse relation indicators. We think, however, that disambiguating the commas in Chinese text is valuable in its own right and is a necessary step in annotating discourse relations.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "\u53cd\u5e94", "sec_num": null }, { "text": "Another complication is that some commaseparated chunks are ambiguous as to whether they should be considered potential arguments in a discourse relation. The chunks marked AO2 and AO4 in (5) are examples of such cases. They, judging from their English translation, may seem clear cases of free adjuncts in PDTB terms (Prasad et al., 2007) , but there is no justification for treating them as such in Chinese. The lack of justification comes from at least three features of Chinese:", "cite_spans": [ { "start": 318, "end": 339, "text": "(Prasad et al., 2007)", "ref_id": "BIBREF3" } ], "ref_spans": [], "eq_spans": [], "section": "\u53cd\u5e94", "sec_num": null }, { "text": "\u2022 Certain words, for instance, \"\u53cd \u5e94\" (\"respond/response\"), \"\u826f \u597d\" (\"well/good\") and \"\u63a5\u53d7\" (\"accept/acceptance\"), are ambiguous with respect to their POS, and when they combine, the resulting sentence may have more than one syntactic analysis. For example, AO3 may be literally translated as \"Companies responded well\" or \"Companies' response was good\". \u2022 There are no inflectional clues to differentiate free adjuncts and main clauses. For example, one can be reasonably certain that \"\u8868 \u793a\" (\"acknowledge\") functions as a verb in (5), however, there is no indication whether it is in the form corresponding to \"acknowledging\" or \"acknowledged\" in English. Or putting it differently, whether one wants to express in Chinese the meaning corresponding to the -ing form or the tensed form in English, the same form \"\u8868\u793a\" could apply. \u2022 Both subject and object can be dropped in Chinese, and they often are when they are inferable from the context. For example, in the twosentence sequence below, the subject of (7) is dropped since it is clearly the same as the subject of the previous sentence in (6) . Since the subject can be omitted from the entire sentence, absence or presence of subject in a clause is not an indication whether the clause is a main clause or a free adjunct, or whether it is part of a VP coordination without a connective. So if we take into account both the lack of differentiating inflectional clues and the possibility of omitting the subject, AO4 in (5) may be literally translated as \"generally acknowledging acceptance\", or \"(and) generally acknowledged acceptance\", or \"(companies) generally acknowledged acceptance\", or \"(companies) generally acknowledged (they) accepted (it)\".", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "\u53cd\u5e94", "sec_num": null }, { "text": "Since in Chinese, there is no reliable indicator distinguishing between main clauses and free adjuncts, or distinguishing between coordination on the clause level without the subject and coordination on the VP level, we will not rely on these distinctions in annotation, as the PDTB team does in their annotation.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "\u53cd\u5e94", "sec_num": null }, { "text": "These basic decisions directly based on linguistic characteristics of Chinese lead to more systematic adaptations to the annotation scheme, to which we will turn in the next subsection.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "\u53cd\u5e94", "sec_num": null }, { "text": "The main consequence of the basic decisions described in Section 3.1 is that we have a whole lot more tokens of implicit relation than explicit relation to deal with. According to a rough count on 20 randomly selected files from Chinese Treebank , 82% are tokens of implicit relation, compared to 54.5% in the PDTB 2.0. Given the overwhelming number of implicit relations, we re-examine where it could make an impact in the annotation scheme. There are three such areas.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Systematic adaptations", "sec_num": "3.2" }, { "text": "In the PDTB, explicit and implicit relations are annotated separately. This is probably partly because explicit connectives are quite abundant in English, and partly because the project evolved in stages, expanding from the more canonical case of explicit relation to implicit relation for greater coverage. When annotating Chinese text, maintaining this procedural division makes much less sense: the landscape of discourse relation (or at least the key elements of it) has already been mapped out by the PDTB work and to set up a separate task to cover 18% of the data does not seem like a worthwhile bother without additional benefits for doing so.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Procedural division between explicit and implicit discourse relation", "sec_num": "3.2.1" }, { "text": "So the question now is how to annotate explicit and implicit relations in one fell swoop? In Chinese text, the use of a discourse connective is almost always accompanied by a punctuation or two (usually period and/or comma), preceding or flanking it. So a sensible solution is to rely on punctuations as the denominator between explicit and implicit relations;and in the case of explicit relation, the connective will be marked up as an attribute of the discourse relation. This unified approach simplifies the annotation procedure while preserving the explicit/implicit distinction in the process.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Procedural division between explicit and implicit discourse relation", "sec_num": "3.2.1" }, { "text": "One might question, at this point, whether such an approach can still call itself \"lexically grounded\". Certainly not if one interprets the term literally ; but in a broader sense, our approach can be seen as an instantiation of a generalized version of it, much the same way that the PDTB is an, albeit different, instantiation of it for English. The thrust of the lexically grounded approach is that discourse annotation should be a data-driven, bottom-up process, rather than a top-down one, trying to fit data into a prescriptive system. Once the insight that a discourse connective functions like a predicate with two ar-guments is generalized to cover all discourse relations, there is no fundamental difference between explicit and implicit discourse relations: both work like a predicate whether or not there is a lexicalization of it. As to what role this distinction plays in the annotation procedure, it is an engineering issue, depending on a slew of factors, among which are cross-linguistic variations. In the case of Chinese, we think it is more economical to treat explicit and implicit relations alike in the annotation process.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Procedural division between explicit and implicit discourse relation", "sec_num": "3.2.1" }, { "text": "To treat explicit and implicit relations alike actually goes beyond annotating them in one pass; it also involves how they are annotated, which we discuss next.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Procedural division between explicit and implicit discourse relation", "sec_num": "3.2.1" }, { "text": "In the PDTB, treatment of implicit discourse relations is modeled after that of explicit relations, and at the same time, some restrictions are put on implicit, but not explicit, relations. This is quite understandable: implicit discourse relations tend to be vague and elusive, so making use of explicit relations as a prototype helps pin them down, and restrictions are put in place to strike a balance between high reliability and good coverage. When implicit relations constitute a vast majority of the data as is the case with Chinese, both aspects need to be re-examined to strike a new balance.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Annotation of implicit discourse relations", "sec_num": "3.2.2" }, { "text": "In the PDTB, annotators are asked to insert a discourse connective that best conveys the implicit discourse relation between two adjacent discourse units; when no such connective expression is appropriate, the implicit discourse relation is further distinguished as \"AltLex\", \"EntRel\", and \"NoRel\". The inserted connectives and those marked as \"Al-tLex\", along with explicit discourse connectives, are further annotated with respect to their senses.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Annotation of implicit discourse relations", "sec_num": "3.2.2" }, { "text": "When a connective needs to be inserted in a majority of cases, the difficulty of the task really stands out. In many cases, it seems, there is a good reason for not having a connective present and because of it, the wording rejects insertion of a connective even if it expresses the underlying discourse relation exactly (or sometimes, maybe the wording itself is the reason for not having a connective). So to try to insert a connective expression may very well be too hard a task for annotators, with little to show for their effort in the end.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Annotation of implicit discourse relations", "sec_num": "3.2.2" }, { "text": "Furthermore, the inter-annotator agreement for providing an explicit connective in place of an implicit one is computed based on the type of explicit connectives (e.g. cause-effect relations, temporal relations, contrastive relations, etc.), rather than based on their identity (Miltsakaki et al., 2004) . This suggests that a reasonable degree of agreement for such a task may only be reached with a coarse classification scheme.", "cite_spans": [ { "start": 278, "end": 303, "text": "(Miltsakaki et al., 2004)", "ref_id": "BIBREF2" } ], "ref_spans": [], "eq_spans": [], "section": "Annotation of implicit discourse relations", "sec_num": "3.2.2" }, { "text": "Given the above two considerations, our solution is to annotate implicit discourse relations with their senses directly, bypassing the step of inserting a connective expression. It has been pointed out that to train annotators to reason about pre-defined abstract relations with high reliability might be too hard a task (Prasad et al., 2007) . This difficulty can be overcome by associating each semantic type with one or two prototypical explicit connectives and asking annotators to consider each to see if it expresses the implicit discourse relation. This way, annotators have a concrete aid to reason about abstract relations without having to choose one connective from a set expressing roughly the same relation or having to worry about whether insertion of the connective is somehow awkward.", "cite_spans": [ { "start": 321, "end": 342, "text": "(Prasad et al., 2007)", "ref_id": "BIBREF3" } ], "ref_spans": [], "eq_spans": [], "section": "Annotation of implicit discourse relations", "sec_num": "3.2.2" }, { "text": "It should be noted that annotating implicit relations directly with their senses means that sense annotation is no longer restricted to those that can be lexically expressed, but also includes those that cannot, notably those labeled \"EntRel/NoRel\" in the PDTB. 2 In other words, we annotate senses of discourse relations, not just connectives and their lexical alternatives (in the case of AltLex). This expansion is consistent with the generalized view of the lexically grounded approach discussed in Section 3.2.1.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Annotation of implicit discourse relations", "sec_num": "3.2.2" }, { "text": "With respect to restrictions on implicit relation, we will adopt them as they prove to be necessary in the annotation process, with one exception. The exception is the restriction that implicit relations between adjacent clauses in the same sentence not separated by a semi-colon are not annotated. This restriction seems to apply mainly to a main clause and any free adjunct attached to it in English; in Chinese, however, the distinction between a main clause and a free adjunct is not as clear-cut for reasons explained in Section 3.1. So this restriction is not applicable for Chinese annotation.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Annotation of implicit discourse relations", "sec_num": "3.2.2" }, { "text": "The third area that an overwhelming number of implicit relation in the data affects is how Arg1 and Arg2 are defined. As mentioned in the introduction, discourse relations are viewed as a predication with two arguments. These two arguments are defined based on the physical location of the connective in the PDTB: Arg2 is the argument expressed by the clause syntactically bound to the connective and Arg1 is the other argument. In the case of implicit relations, the label is assigned according to the text order.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Definition of Arg1 and Arg2", "sec_num": "3.2.3" }, { "text": "In an annotation task where implicit relations constitute an overwhelming majority, the distinction of Arg1 and Arg2 is meaningless in most cases. In addition, the phenomenon of parallel connectives is predominant in Chinese. Parallel connectives are pairs of connectives that take the same arguments, examples of which in English are \"if..then\", \"either..or\", and \"on the one hand..on the other hand\". In Chinese, most connectives are part of a pair; though some can be dropped from their pair, it is considered \"proper\" or formal to use both. (8) below presents two such examples, for which parallel connectives are not possible in English. In the PDTB, parallel connectives are annotated discontinuously; but given the prevalence of such phenomenon in Chinese, such practice would generate a considerably high percentage of essentially repetitive annotation among explicit relations.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Definition of Arg1 and Arg2", "sec_num": "3.2.3" }, { "text": "So the situation with Chinese is that distinguishing Arg1 and Arg2 the PDTB way is meaningless in most cases, and in the remaining cases, it often results in duplication. Rather than abandoning the distinction altogether, we think it makes more sense to define Arg1 and Arg2 semantically. It will not create too much additional work beyond distinction of different senses of discourse relation in the PDTB. For example, in the semantic type CONTIN-GENCY:Cause, we can define \"reason\" as Arg1 and \"result\" as Arg2. In this scheme, no matter which one of \u56e0 (\"because\") and \u6545 (\"therefore\") appears without the other, or if they appear as a pair in a sentence, or if the relation is implicit, the Arg1 and Arg2 labels will be consistently assigned to the same clauses.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Definition of Arg1 and Arg2", "sec_num": "3.2.3" }, { "text": "This approach is consistent with the move from annotating senses of connectives to annotating senses of discourse relations, pointed out in Section 3.2.2. For example, in the PDTB's sense hierarchy, \"reason\" and \"result\" are subtypes under type CON-TINGENCY:Cause: \"reason\" applies to connectives like \"because\" and \"since\" while \"result\" applies to connectives like \"so\" and \"as a result\". When we move to annotating senses of discourse relations, since both types of connectives express the same underlying discourse relation, there will not be further division under CONTINGENCY:Cause, and the \"reason\"/\"result\" distinction is an intrinsic property of the semantic type. We think this level of generality makes sense semantically.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Definition of Arg1 and Arg2", "sec_num": "3.2.3" }, { "text": "To test our adapted annotation scheme, we have conducted annotation experiments on a modest, yet significant, amount of data and computed agreement statistics.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Annotation experiment", "sec_num": "4" }, { "text": "The agreement statistics come from annotation conducted by two annotators in training so far. The data set consists of 98 files taken from the Chinese Treebank . The source of these files is Xinhua newswire. The annotation is carried out on the PDTB annotation tool 3 .", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Set-up", "sec_num": "4.1" }, { "text": "To evaluate our proposed scheme, we measure agreement on each adaption proposed in Section 3, as well as agreement on argument span determination. Whenever applicable, we also present (roughly) comparable statistics of the PDTB (Miltsakaki et al., 2004) . The results are summarized in Table 1 overall-bnd-14039* 87.7 N/A (87.5/87.9) Table 1 : Inter-annotator agreement in various aspects of Chinese discourse annotation: rel-ident, discourse relation identification; rel-type, relation type classification; imp-sns-type, classification of sense type of implicit relations; arg-order, order determination of Arg1 and Arg2. For agreement on argument spans, the naming convention is --. exp: explicit relations; imp: implicit relations; span: argument span;", "cite_spans": [ { "start": 228, "end": 253, "text": "(Miltsakaki et al., 2004)", "ref_id": "BIBREF2" } ], "ref_spans": [ { "start": 286, "end": 293, "text": "Table 1", "ref_id": null }, { "start": 334, "end": 341, "text": "Table 1", "ref_id": null } ], "eq_spans": [], "section": "Inter-annotator agreement", "sec_num": "4.2" }, { "text": "xm: exact match; pm: partial match; bnd: boundary. *: number of tokens agreed on by both annotators.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Inter-annotator agreement", "sec_num": "4.2" }, { "text": "The first adaption we proposed is to annotate explicit and implicit discourse relations in one pass. This introduces two steps, at which agreement can each be measured: First, the annotator needs to make the judgment, at each instance of the punctuations, whether there is a discourse relation (a step we call \"relation identification\"); second, once a discourse relation is identified, the annotator needs to classify the type as one of \"Explicit\", \"Implicit\", or \"AltLex\" (a step we call \"relation type classification\"). The agreement at these two steps is 95.4% and 95.1% respectively.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Inter-annotator agreement", "sec_num": "4.2" }, { "text": "The second adaption is to bypass the step of inserting a connective when annotating an implicit discourse relation and classify the sense directly. The third adaptation is to define Arg1 and Arg2 semantically for each sense. To help annotators think about relation sense abstractly and determine the order of the arguments, we put a helper item alongside each sense label, like \"Causation: \u56e0 \u4e3aarg1\u6240 \u4ee5arg2\" (\"Causation: because arg1 therefore arg2\"). This approach works well, as evidenced by 87.4% 4 and 99.8% agreement for the two processes respectively.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Inter-annotator agreement", "sec_num": "4.2" }, { "text": "To evaluate agreement on determining argument span, we adopt four measures. In the first three, explicit and implicit relations are calculated separately (although they are actually annotated in the same process) to make our results comparable to the published PDTB results. Each argument span is treated as an independent token and either exact or partial match (i.e. if two spans share one boundary) counts as 1. The fourth measure is less stringent than exact match and more stringent than partial match: It groups explicit and implicit relation together and treats each boundary as an independent token. Typically, an argument span has two boundaries, but it can have four (or more) boundaries when an argument span is interrupted by a connective and/or an AltLex item.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Inter-annotator agreement", "sec_num": "4.2" }, { "text": "Evidently, determining argument span is the most challenging aspect of discourse annotation. However, it should be pointed out that agreement was on an overall upward trend, which became especially prominent after we instituted a restriction on implicit relations across a paragraph boundary towards the end of the training period. It restricts full anno- 4 Two more points should be made about this number. First, it may be partially attributed to our differently structured sense hierarchy. It is a flat structure containing the following 12 values: ALTERNATIVE, CAUSATION, CONDITIONAL, CONJUNC-TION, CONTRAST, EXPANSION, PROGRESSION, PURPOSE, RESTATEMENT, TEMPORAL, EntRel, and NoRel. Aside from including EntRel and NoRel (the reason and significance of which have been discussed in Section 3.2.2), the revision was by and large not motivated by Chinese-specific features, so we do not address it in detail in this paper. Second, in making the comparison with the PDTB result, the 12-value structure is collapsed into 5 values: TEMPORAL, CONTINGENCY, COMPARISON, EX-PANSION, and EntRel/NoRel, which must be different from the 5 values in Miltsakaki et al. (2004) , judging from the descriptions. tation to only three specific situations so that most loose and/or hard-to-delimit relations across paragraph boundaries are excluded. This restriction appears to be quite effective, as shown in Table 2 .", "cite_spans": [ { "start": 356, "end": 357, "text": "4", "ref_id": null }, { "start": 1142, "end": 1166, "text": "Miltsakaki et al. (2004)", "ref_id": "BIBREF2" } ], "ref_spans": [ { "start": 1395, "end": 1402, "text": "Table 2", "ref_id": null } ], "eq_spans": [], "section": "Inter-annotator agreement", "sec_num": "4.2" }, { "text": "Overall Arg Span of boundary span-em rel.'s F(p/r) (%) (%) last 5 wks 1103 90.0 (90.0/89.9) 80.8 last 3 wks 677 91.0 (91.0/91.0) 82.5 last 2 wks 499 91.8 (91.8/91.8) 84.2 Table 2 : Inter-annotator agreement on argument span during the last 5 weeks of training.", "cite_spans": [ { "start": 149, "end": 165, "text": "91.8 (91.8/91.8)", "ref_id": null } ], "ref_spans": [ { "start": 171, "end": 178, "text": "Table 2", "ref_id": null } ], "eq_spans": [], "section": "num", "sec_num": null }, { "text": "We have presented a discourse annotation scheme for Chinese that adopts the lexically ground approach of the PDTB while making systematic adaptations motivated by characteristics of Chinese text. These adaptations not only work well in practice, as evidenced by the results from our annotation experiment, but also embody a more generalized view of the lexically ground approach to discourse annotation: Discourse relations are predication involving two arguments; the predicate can be either covert (i.e. Implicit) or overt, lexicalized as discourse connectives (i.e. Explicit) or their more polymorphous counterparts (i.e. AltLex). Consistent with this generalized view is a more semantically motivated sense annotation scheme: Senses of discourse relations (as opposed to just connectives) are annotated; and the two arguments of the discourse relation are semantically defined, allowing the sense structure to be more general and less connective-dependent. These framework-level generalizations can be applied to discourse annotation of other languages.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Conclusions", "sec_num": "5" }, { "text": "not necessarily represent the view of the National Science Foundation.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Conclusions", "sec_num": "5" }, { "text": "Thus \"EntRel\" and \"NoRel\" are treated as relation senses, rather than relation types, in our scheme.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "", "sec_num": null }, { "text": "http://www.seas.upenn.edu/\u223cpdtb/tools.shtml#annotator", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "", "sec_num": null } ], "back_matter": [ { "text": "This work is supported by the IIS Division of the National Science Foundation via Grant No. 0910532 entitled \"Richer Representations for Machine Translation\"and by the CNS Division via Grant No. 0855184 entitled \"Building a community resource for temporal inference in Chinese\". All views expressed in this paper are those of the authors and do", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Acknowledgments", "sec_num": null } ], "bib_entries": { "BIBREF0": { "ref_id": "b0", "title": "Building a Discourse-Tagged Corpus in the Framework of Rhetorical Structure Theory", "authors": [ { "first": "Lynn", "middle": [], "last": "Carlson", "suffix": "" }, { "first": "Daniel", "middle": [], "last": "Marcu", "suffix": "" }, { "first": "Mary", "middle": [ "Ellen" ], "last": "Okurowski", "suffix": "" } ], "year": 2003, "venue": "Current Directions in Discourse and Dialogue", "volume": "", "issue": "", "pages": "", "other_ids": {}, "num": null, "urls": [], "raw_text": "Lynn Carlson, Daniel Marcu, and Mary Ellen Okurowski. 2003. Building a Discourse-Tagged Corpus in the Framework of Rhetorical Structure Theory. In Current Directions in Discourse and Dialogue. 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Natural Lan- guage Engineering, 11(2):207-238.", "links": null }, "BIBREF5": { "ref_id": "b5", "title": "Annotating the Discourse Connectives in the Chinese Treebank", "authors": [ { "first": "Nianwen", "middle": [], "last": "Xue", "suffix": "" } ], "year": 2005, "venue": "Proceedings of the ACL Workshop on Frontiers in Corpus Annotation", "volume": "", "issue": "", "pages": "", "other_ids": {}, "num": null, "urls": [], "raw_text": "Nianwen Xue. 2005. Annotating the Discourse Con- nectives in the Chinese Treebank. In Proceedings of the ACL Workshop on Frontiers in Corpus Annotation, Ann Arbor, Michigan.", "links": null } }, "ref_entries": { "TABREF1": { "num": null, "html": null, "type_str": "table", "text": "According to reports, [ AO1 Dongguan District Customs accepted more than 8400 records of company contracts], [ AO2 a slight increase from before the pilot]. [ AO3 Companies responded well], [ AO4 generally acknowledging acceptance].\"", "content": "
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respond/responsewell/good,generally
\u8868\u793a\u63a5\u53d7 ]\u3002
acknowledgeaccept/acceptance.
\"
" }, "TABREF2": { "num": null, "html": null, "type_str": "table", "text": "S1 In the past five years, Shanghai strengthened the connection of its port to other areas of the country through actively procuring export supplies from other provinces and cities, and through organizing events such as the East China Export Commodities Fair.]\"", "content": "
\u534e\u4e1c\u51fa\u53e3\u5546\u54c1\u4ea4\u6613\u4f1a\u7b49
ExportCommodityFairetc.event,
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\"[ (7) [ S2 \u540c\u65f6\uff0c \u53d1\u5c55
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exportsupply,organizeChinaEast
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ChinesePDTB
tkn no. F(p/r) (%)(%)
rel-ident3951*95.4 (96.0/94.7)N/A
rel-type395195.1N/A
imp-sns-type296787.472
arg-order305999.8N/A
argument span
exp-span-xm158084.290.2
exp-span-pm158099.694.5
imp-span-xm593476.985.1
" } } } }