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  • Original Article
  • Open Access

Semantic relation identification for consecutive predicative constituents in Chinese

  • 1Email author,
  • 2,
  • 2,
  • 2 and
  • 2
Lingua Sinica20173:9

https://doi.org/10.1186/s40655-017-0028-1

  • Received: 6 June 2016
  • Accepted: 25 August 2017
  • Published:

Abstract

In this paper, we propose a general methodology for designing semantic role/relation system. Based on this methodology, we establish a succinct semantic relation system for consecutive predicative constituents for Chinese, which includes serial verb construction, discourse construction, and other constructions describing serial events. This semantic relation system has 13 middle-level classes and 24 fine-grained sub-classes in contrast to conventional complex classification schemes and meets the uniqueness and completeness criteria of semantic relation identification. We conduct experiments on our system by training four annotators in 1 h to label 200 sentences extracted from Sinica Treebank and HIT-CDTB. With the help of our predesigned feature-based decision tree and a connective markers checklist, the annotators attain a 73% consistency with the reference standard annotation and substantial agreement by Cohen’s kappa coefficient for middle-level labeling. By analyzing the labeling error types, we slightly revise our classification scheme and propose six methods to improve the classification and labeling system, hoping to achieve even better agreement in the future.

Keywords

  • Semantic relation identification
  • Semantic roles
  • Feature-based semantic relation system
  • Serial verb construction
  • Discourse construction
  • Discourse relation recognition

1 Introduction

Essential to natural language understanding are the processes of part-of-speech tagging, parsing, and semantic relation identification. In this paper, our objective is to clarify the relations between consecutive predicative constituents (abbreviated CPCs), which include serial verb construction (abbreviated SVC), discourse construction, and other constructions describing serial events in Chinese text and to find a good and workable semantic relation system for semantic role/relation labeling tasks. As a consequence, a methodology of semantic role/relation design methodology was also established.

Chinese has various constructions to juxtapose two predicative constituents, such as compounding, coordinate constructions, serial verb constructions, and discourse constructions. Each CPC may be with/without an overt syntactic marking of the semantic relation between the described events, for example, 戰敗投降 zhànbài tóu xiáng 'defeated and surrendered'. Whereas in English the conjunction and is used to mark a simple coordination or temporal succession between VPs, in Chinese, the two VP constituents are simply adjoined. CPCs may occur in a simple sentence, as shown in (1a) and (1b), and are termed serial verb construction (Aikhenvald 2006; Lin et al. 2012; Tao 2009); that which occurs with coherent sequences of sentences as given in (1c) is called discourse construction (Hovy and Maier 1992; Prasad et al. 2008; Wolf and Gibson 2005).
  1. (1)
    1. a.

      大人們趕著上山(V1)打虎(V2)           means-purpose

      dàrénmen__gǎnzhe__shàngshān__dǎhǔ

      the-adults__hurried__go-uphill__hunt-the-tiger

      The adults hurried to go uphill (V1) to hunt the tiger (V2).

       
    2. b.

      一大早上山(V1)累壞(V2)學生了         cause-result

      yīdàzǎo__shàngshān__lèihuài__xuésheng__le

      early-in-the-morning__go-up-hill__tire-out__student__LE

      It tired the students out (V2) to go uphill (V1) early in the morning.

       
    3. c.

      如遇下雪(V1), 一般車輛避免(V2)上山, 以免發生(V3)危險

      condition-result between V1 and V2; event-avoidance between V2 and V3

      rú__yù__xiàxuě__yībān__chēliàng__bìmiǎn__shàngshān,__yǐmiǎn__ fāshēng__wéixiǎn

      if__encounter__snow__ordinary__vehicle__avoid__go-up-hill,__lest__ occur__danger

      If it snows (V1), it is better to avoid (V2) driving uphill lest danger occurs (V3).

       

    Most studies discuss different constructions separately. However, when studying semantic relations between CPCs in different constructions, it is not necessary to regard them as distinct phenomena. Zhou and Xue (2012) described four characteristics which blur the boundary between discourse construction and serial verb construction. They are as follows: (i) semi-colon is not always used to separate the sentences; (ii) in most of the cases, no explicit discourse connectives are used to denote the discourse relations; (iii) no inflectional clues to differentiate free adjuncts and main clauses; and (iv) both subject and object can be dropped in Chinese. For instance in (2), there are no essential reasons we need to separate (a) and (b) into different categories of discourse construction and serial verb construction.

     
  2. (2)
    1. a.

      她丈夫車禍過世了。 SVC

      tā__zhàngfu__chēhuò__guòshì__le

      she__husband__car-accident__died

      Her husband died in a car accident.

       
    2. b.

      她丈夫車禍, 所以過世了。 Discourse Construction

      tā__zhàngfu__chēhuò,__suǒyǐ__guòshì__le

      she__husband__car-accident,__so__died

      Her husband met with a car accident, so died.

       

    In this paper, we are targeting to identify semantic relations between CPCs in Chinese. However, our proposed design methodology is applicable to develop all semantic relation systems not limited to consecutive predicative units. To focus our studies, we exclude predicate-argument relations in our discussion and we do not account for the problem of delimiting related and unrelated two predicative constituents.

     

To sum up, CPCs are beyond any syntactic restriction, indicating the constructions including two events which describe the same subject or an identical topic such as discourse construction, serial verb construction, modifier–event construction (e.g., 傷重過世 shāngzhòng guòshì ‘seriously injured and died’), and causal event–resultative event construction (e.g., 過世留下遺產 guòshì liúxià yíchǎn ‘died and left a legacy’). In this paper, we aim to distinguish the relation between both inter- or intra-sentential CPCs; not only discourse construction and SVC are included but also sentences modified by a prepositional phrase or a complemental phrase are all taken into account. By following our design methodology, we integrate different surface forms of Chinese constructions from Sinica Treebank (Chen and Huang 2004) and HIT-CDTB (Zhang et al. 2014). It results in a hierarchical relation system of 24 fine-grained semantic relations, practically achieving the completeness and uniqueness criteria of relation identification.

The rest of the paper is organized as follows. In Section 2, we provide necessary background information and address the importance of design methodologies for semantic relation system. After introducing the distinction between semantic role labeling and semantic relation identification, we review the relevant literatures in Section 2.2. In Section 3, we motivate the need for a new relation system and propose a feature-based design methodology in Section 3.1. Following that, in Section 3.2, we describe the design of our semantic relation system; in Section 4, a guideline for semantic relation identification is addressed, and an experiment to verify the completeness and distinctness of subordinate relations is described and discussed in Section 5. We conclude the paper in Section 6.

2 Background

2.1 Semantic roles and semantic relations

Semantic role is the role of a dependent daughter with respect to its head constituent. On the other hand, semantic relation means relations between any two related constituents. Therefore, semantic relations have a broader coverage than head-dependent relations, since other than head-dependent relations, they also include coordinate relations and discourse relations.

Conventional text annotation, such as treebanks, might annotate syntactic dependent structures and semantic roles of constituents, such as Sinica Treebank (Chen et al. 2003). How is the semantic role of a dependent daughter determined? Usually, it is a result of considering the parameters of head constituent, dependent daughter, role marker, and phrasal/sentential pattern. By those factors, we decide a best role to describe this dependent daughter. The premise of above role assignment scheme is that there is only one semantic role for each dependent daughter and there is a limited set of predetermined semantic roles which you may choose from. Such a simple schema annotates only the semantic role of dependent daughter of head-dependent relations without considering coordinate relations and relations across sentences, such as discourse relations. Furthermore, a naïve role labeling system may cause the following problems.

First of all, each constituent may have dependent relations with multiple heads. For instance, in (3), an object of a verb-result compound in Chinese has two dependent relations. One is relation with respect to verb part and the second relation is with result part. Each bears different semantic relation. However, only single role is assigned to each dependent daughter. As a matter of fact, multiple relations commonly exist in a discourse structure, for example topic-comment chains.
  1. (3)

    張三打破花瓶 (The vase is the patient of 打 ‘hit’ or theme of 破 ‘broken’.)

    zhāngsān__dǎpò__huāpíng

    Zhangsan__hit__broken__vase

    Zhangsan breaks the vase.

     
  2. (4)

    花瓶打破了 (The vase is the theme of 破  ‘broken’.)

    huāpíng__dǎpò__le

    vase__hit__broken__LE

    The vase was broken.

     

The second problem is none-exclusiveness of semantic roles/relations. Semantic roles/relations may categorize into different feature dimensions. The relations between two constituents may be described by different categories of relations. For example in (3), the role of 花瓶 huāpíng ‘vase’ may be described by either dynamic relation of patient or static relation of theme. Similarly temporal relations, cause-result relations are falling into two different feature dimensions and the two relations may co-exist in CPCs. Conventionally, semantic roles may each other share the same characteristics and have idiosyncrasies. Each semantic role can be characterized by a few semantic features. The best role describing a dependent daughter is the role which matches most semantic features of the target constituent in its contextual environment (Dowty 1991). It causes competition among several possible candidate roles. Then, to determine the best role, in addition to feature matching, should each feature assign different weights in different contextual environments?

It results in a third practical problem: if a semantic role system is too complicated, it is very hard to annotate the best role/relation. Since a semantic role of a constituent is determined not only by the semantic relation with its dependent head but also by the entire contexture environment of the constituent. As we had mentioned, the major parameters for semantic role determination are head, dependent daughter, role marker, and phrasal/sentential pattern. Such criteria cause the complication of determining the best semantic role as exemplified in (5–7).
  1. (5)
    1. a.

      張三被屠殺。(Zhangsan is the patient of “slaughter”; it focused on the dynamic feature dimension.)

      zhāngsān__bèi__túshā

      Zhangsan__BEI__slaughtered

      Zhangsan was slaughtered.

       
    2. b.

      張三遭屠。 (Zhangsan is the theme of “being slaughtered”; it focused on the static feature dimension.)

      zhāngsān__zāotú

      Zhangsan__ZAO__slaughtered

      Zhangsan was slaughtered.

       
     
  2. (6)
    1. a.

      張三把牛肉軟化了 (Role marker delimits “beef” as a patient, i.e. instead of the main verb, becomes the head.)

      zhāngsān__bǎ__niúròu__ruǎnhuà__le

      Zhangsan__BA__beef__soften

      Zhangsan softened the beef.

       
    2. b.

      牛肉軟化了 (“Beef” is the theme of “soften”.)

      niúròu__ruǎnhuà__le

      beef__soften

      The beef is softened.

       
     
  3. (7)

    他買票(V1)上車(V2)。 (Do temporal relation, condition-consequence, cause-result, or elaboration all exist between V1 and V2?)

    tā__mǎipiào__shàngchē

    he__buy__ticket__get-on-the-bus

    He bought a ticket (V1) and got on the bus (V2).

     

A better relational system for human annotators and also for future automation should meet the criteria of uniqueness and completeness; Uniqueness means two CPCs may assign a semantic relation (mostly are formed by a pair of semantic roles) which best describes their semantic relation. Completeness means two CPCs may be assigned some semantic role(s) to describe their semantic relations. That is, semantic relations between two CPCs are best described by one of the relation labels in the system without ambiguity.

Therefore, in designing a semantic relation system for CPCs, we encounter the following problems: How many relations are needed to meet the completeness criterion, that is, are all semantic relations between CPCs covered by the proposed classification system? How to meet the uniqueness criterion, that is, achieve a unique and consistent best labeling for CPCs? In the meanwhile, should we allow multiple relations while different interpretations occur? In the following subsections, by studying the related work and summarizing previous systems and offering our viewpoints, we attempt to answer the above questions and come up with a workable design methodology and a practical semantic relation system.

2.2 Related works

In the late 1980s, Mann and Thompson (1988) proposed a new interpretation of rhetorical structure theory (abbreviated RST) to describe natural texts, characterizing their structure primarily in terms of relations that hold between parts of the text. By examining real data, they provided a list which enumerates those which have proven the most useful 23 relations, including circumstance, solutionhood, elaboration, background, enablement, and motivation. Continuing the RST framework, Carlson and Marcu (2001; RST-DT) in their tagging reference manual claimed 16 classes covering a total of 78 relations, including attribution, background, cause, comparison, and condition.

Hovy and Maier (1992) summarized a survey of the conclusions of approximately 30 researchers who proposed more than 400 intersegment relations in different classification systems. Hovy then suggested using just as many relations as are required for determining the major aspects of English discourse structure, that is, approximately 70 relations, organized into a hierarchy of increasing specificity. The top-level classifications are divided into three parts: Ideational relation is defined between adjacent segments of material as those relations that express some experience of the world about us and within our imagination, for example, circumstance, cause/result, and general condition. Interpersonal relation is defined as holding between adjacent segments of textual material by which the author attempts to affect the address’s beliefs, attitudes, desire, and so on, by means of language, for example, interpretation and enablement. Textual relation is defined as holding between adjacent segments of text which exists solely due to the juxtaposition imposed by the nature of the presentation medium, for example conjunction and pre-sequence.

Miltsakaki et al. (2008) proposed four classes covering a total of 38 fine-grained relations which are annotated to the Penn Discourse Treebank (abbreviated PDTB), the largest-scale annotated corpus at the discourse level. Their relation structure is therefore most prevalent. The top-level classifications are divided into four parts: temporal is used when the situations described in the arguments are related temporally; contingency is used when the situations described in the arguments are causally influenced; comparison applies when a discourse relation is established between arguments in order to highlight prominent differences between the two situations; and expansion groups all the relations which expand the discourse and move forward its narrative or exposition.

Based on the lexically grounded approach of PDTB, Zhou and Xue (2012, 2015) presented a Chinese discourse annotation scheme and focused on the key characteristics of Chinese text which differs from English that we have mentioned in previous section. They claimed promising results on identifying a discourse relation; classifying the semantic type of explicit, implicit, or altLex; and determining the argument span. The agreements of the former are both over 95%, and the latter is over 80%.

Also based on PDTB classification, Huang et al. (2014) adopted discourse connectives to reveal explicit discourse relation in Chinese. They found there are 808 Chinese connectives which are eight times more than English connectives. Moreover, the Chinese discourse connectives have a variety of parts of speech that further deepen the difficulties of Chinese discourse relation labeling. By using semi-supervised learning method, the labeling result shows an F-score of 73.22%.

Zhou et al. (2014) followed the annotation scheme of PDTB and presented the first open discourse treebank for Chinese (abbreviated DTBC). They modified the PDTB sense hierarchy; three type level senses (i.e., CONTINGENCY. Inference, CONTINGENCY. Purpose and EXPANSION. Background) and two subtype level senses (i.e., EXPANSION. Conjunction. parallel and EXPANSION. Conjunction. progressive) were added to meet the needs of Chinese textual characteristics. They reported an over 90% inter-annotator agreement on discourse connective identification and an over 85% on sense annotation.

Li et al. (2014), based on the annotation of discourse connective in the Chinese discourse treebank (abbreviated CDTB), propose a three-level classification with a total of 17 fine-grained relations. The top-level classifications are divided into causality, transition, coordination, and explanation, and the third level merely lists the corresponding connective markers belonging to the middle-level types. The CDTB annotation is done by five long-term training annotators. The result showed a 94% inter-annotator agreement on explicit or implicit identification, an 82.3% agreement on explicit connective identification, and a 74.6% on implicit connective insertion.

Regarding practical relation identification problems, Wang et al. (2010) interpreted the implicit semantic relation between N-N compounds by adopting a dynamic approach using paraphrasing verbs. Not giving a set of relation candidates, they recognized each relation of N-N compounds by collocate verbs, for example, through Chinese word sketch engine finding people tell/seek a 愛情故事 àiqíng gùshì ‘love story’; and 民間故事 mínjiān gùshì ‘folk tales’ are stories that come from/spread in villages, then further recognize the fine-grained differences of meaning between the related compounds. On the contrary, Hong and Huang (2015) revealed the semantic relation between V-V compounds using an ontology-based conceptual classification, where three types of eventive relations, i.e., coordinate, modificational, and resultative, are predicted automatically. Xu and Huang (2014) discriminated sentences into general events, speech act, and modality types which is namely a task of event type classification.

3 Our semantic relation system

As given above, many classification systems for discourse relations had been established and experiments on different aspects of discourse relations were carried out. The proposed systems were proven to be sound. Unfortunately, hardly any previous mentioned systems meet the uniqueness criterion, since it is almost impossible to achieve mutually exclusivity for all relations. We agree that multi-relation interpretations between CPCs do exist but to achieve a unique annotation scheme which is also in line with the procedure of human understanding, i.e., always select the best interpretation among many possibilities. Therefore, our semantic relation system adopts a feature-based decision-making methodology described below to achieve the best labeling.

3.1 Methodology for designing a semantic role system

Our proposed design methodology tries to provide a methodology for designing a semantic relation system to avoid the problems caused by conventional semantic role labeling system mentioned in the Section 2.1 and to achieve the uniqueness and completeness criteria of relation identification.

To deal with the first problem of multiple roles, we suggest labeling semantic relation between any two related constituents instead of semantic roles, i.e., each constituent may have many relations each with respect to a different related constituent.

For the problem of ambiguous role assignment caused by none-exclusiveness of semantic roles/relations, we propose a multi-level refinement and feature-based approach. A relation system should be designed in a hierarchical way from top level to bottom level. Each level of relations is differentiated by a salient feature from top to bottom to form a binary branching. For instance, the most salient feature to differentiate CPCs relations is +realis. Two types of relations are divided. One is relations regarding realis events (facts) and another is relations regarding irrealis events (opinions). We then refine each type of relations into different levels of fine-grained relations according to different dimension of relation types and semantic features from different aspects. For instance, the realis relations can be refined according to the feature of +intension into relations with purpose and relations without purpose. The resulting hierarchical relation system is also formed a decision tree which is utilized to find the unique best relation among ambiguous multiple relations to achieve the uniqueness criterion. As for the criterion of completeness, we propose a corpus-based approach; each preliminary designed feature-based semantic relation system should be tested and verified by a large set of real data from corpora. New features and new relations can be added, and the preliminary system will be refined accordingly until all real data can be satisfied.

3.2 Our design

For the first step, we integrate and rearrange relations proposed by previous frameworks to meet the needs of Chinese syntactic and semantic constructions, including SVC and discourse constructions, and use semantic features as discriminative criteria. By combining the relations with E-HowNet (Chen et al. 2005; Chen 2011) semantic role system, which is a lexical knowledge base consisting of definitions for lexical senses, where more than 100 semantic relations are used to describe the sense relations, we then classify the possible candidate relations by observing their salient features and eliminating redundant relations as well as relations with minor differentiation features. We end up in developing a preliminary three-level semantic relation framework for CPCs as shown in Fig. 1.
Fig. 1
Fig. 1

Relations between CPCs

The top-level classification is divided into Description and Opinion according to the feature of realis. Description is used principally to indicate that something is a statement of fact, for example in 他生病(V1)住院(V2) tā shēngbìng zhùyuàn ‘he was sick and stayed in the hospital’, a cause-result relation under description is revealed between V1 and V2. Opinion is used to express the speaker’s attitude towards something, for example, in 如果生重病(V1)就要住院(V2) rúguǒ shēngzhòngbìng jiùyào zhùyuàn ‘if seriously ill, one must stay in the hospital’, a condition-result relation is revealed between V1 and V2 to express the speaker’s attitude. Clearly, the diversity of the two top-level classes can be distinguished by the realis and irrealis moods in the grammatical category since opinion does not focus on a situation or action that has actually occurred. Therefore, in order to meet the uniqueness criterion, adding discrimination features such as realis, intentional, and temporal to each semantic relation may help to determine the primary relations between CPCs as exemplified below:
  1. (8)
    purpose[+intentional]
    1. a.
      causality[-intentional] vs. purpose[+intentional]
      1. a1.

        搶劫(V1)被逮(V2)           cause-result vs.

        qiǎngjié__bèidǎi

        rob__be-caught

        robbed and be caught

         
      2. a2.

        蒐證(V1)舉發(V2)          means-purpose

        sōuzhèng__jǔfā

        gather-evidence__expose-one’s-secret

        gather evidence to expose one’s secret

         
       
    2. b.
      purpose[+intentional] vs. background[-intentional]
      1. b1.

        出國(V1)留學(V2)           means-purpose vs.

        chūguó__liúxué

        go-abroad__study-abroad

        study abroad

         
      2. b2.

        搭機(V1)前往(V2)          manner- head event

        dājī__qiánwǎng

        take-plane__leave-for

        go by airplane

         
       
    3. c.
      purpose[+intentional] vs. sequence[-intentional]
      1. c1.

        整裝(V1)出門(V2)           means-purpose vs.

        zhěngzhuāng__chūmén

        dress__go-out

        dressed to go out

         
      2. c2.

        放學(V1)回家(V2)          TimeBefore-TimeAfter

        fàngxué__huíjiā

        leave-school__go-home

        go home after school

         
       

    Since the type of purpose implies an intention behind an action, it is an effective feature to distinguish it from the other types as shown in (8). Comparatively, events labeled with purpose contain intention and motivation which lead the actor to pursue his act. On the contrary, the actors are less aware of what they can achieve by engaging in an action related with causality, background, or sequence relation types.

     
As illustrated below, and and listing are other subordinate types discriminated by the temporal feature.
  1. (9)
    and [+temporal] vs. listing [-temporal]
    1. a.

      忽然宣佈(V1)關閉機場, 也下令(V2)禁止所有集會活動           and vs.

      hūrán__xuānbù__guānbì__jīchǎng, yě__xiàlìng__jìnzhǐ__suǒyǒu__jíhuì__huódòng

      suddenly__announce__close__airport, also__order__forbid__all__gathering__activity

      Suddenly the closure of the airport was announced, and all gatherings were banned too.

       
    2. b.

      暫停包括香港飛(V1)臺北, 以及臺北飛(V2)香港航班          listing

      zhàntíng__bāokuò__xiānggǎng__fēi__táiběi,__yǐjí__táiběi__fēi__ xiānggǎng__hángbān

      pause__including__Hong-Kong__fly__Taipei,__and__Taipei__fly__Hong-Kong__flight

      Paused flights include Hong Kong to Taipei and Taipei to Hong Kong.

       

    Belonging to the synchronous type, and is used to connect events that occur at the same time, while listing is simply used to link items being described that are not involved within the timeline. And is also easily confused with apposition, and apposition sometimes confused with result; (10) and (11) demonstrate the difference between these subtypes.

     
  2. (10)
    and [−synonym] vs. apposition [+synonym]
    1. a.

      一群人又跳(V1)又叫(V2)         and vs.

      yīqúnrén__yòu__tiào__yòu__jiào

      a-group-of-people__and__dance__and__shout

      A group of people dancing and shouting.

       
    2. b.

      把自己好好梳妝(V1)打扮(V2)一番          head event-apposition

      bǎ__zìjǐ__hǎohǎo__shūzhuāng__dǎbàn__yīfān

      ba__oneself__well__decorate__dress-up__once

      dress and decorate oneself properly.

       
     
  3. (11)
    apposition [+synonym] vs. result [+result state]
    1. a.

      被騙(V1)上當(V2)           head event-apposition vs.

      bèipiàn__shàngdàng

      be-cheated__be-fooled

      be cheated and fooled

       
    2. b.

      哭(V1)不停(V2)          head event-result

      kū__bùtíng

      cry__not-stop

      cries continuously

       

    Apposition is established only when V1 and V2 are synonymous; result is assigned when the second event denotes the result state of the first action. Along with these features, each subordinate type and subtype in Fig. 1 has been defined specifically; see Appendix 1; connective words that help reveal explicit relations are also attached to each correspondent subtype; see Appendix 2, Table 4.

     

To meet the completeness criterion, we have tried to identify as many semantic relations as possible that CPCs may have and we define the relation of elaboration and addition rather flexible and inclusive, which makes the completeness criterion easier to be achieved. The completeness criterion is verified by labeling over 50 paragraphs in HIT-CIR Chinese Discourse Relation Corpus (HIT-SCIR 哈工大社会计算与信息检索研究中心 2013) and 3000 sentences in Sinica Treebank (Chen and Huang 2004), to ensure sufficient coverage of the relations shown in Fig. 1 for Mandarin Chinese.

4 Guideline for semantic relation identification

4.1 Three factors that affect the deduction of relation recognition

Summarizing the factors that affect the deduction of relation recognition, other than senses of two events, three main aspects are primary considerations: markers, event ordering, and knowledge-based reasoning. At surface structures, conjunctions and adverbial markers are used to mark fixed explicit relations between subevents, as shown in (12). However, not all CPCs have explicit relation markers. In most cases, the logical relations between two events require common-sense knowledge to determine. Also, the ordering of the VPs may indicate the relationship between subevents, such as in (13): V1 always precedes V2 in the timeline to introduce an intention behind the action or a consequential result of the state. However, this is not an absolute constraint. In rhetoric, we may see sentences like 趕考進京 gǎnkǎo jìn jīng ‘to sit a civil service examination (he) goes to the capital’ as well, or as in the sentences given in (14), both orderings are commonly used.
  1. (12)
    1. a.

      他吃(V1)完走(V2)           TimeBefore-TimeAfter

      tā__chī__wán__jiù__zǒu

      he__eat__finished__afterwards__left

      He finished the meal and left.

       
    2. b.

      坐(V1)看(V2)書           manner-head event

      zuò__zhe__kànshū

      sit__ZHE__read

      sit and read.

       
    3. c.

      美(V1)沒話說(V2)           head event-result

      měi____méihuàshuō

      beautiful__DE__hard-to-describe

      [It is] too beautiful to describe.

       
    4. d.

      雖然窮(V1)還是快樂(V2)           concession-disjunctive

      tā__suīrán__qióng__háishì__kuàilè

      he__although__poor__still__happy

      He is poor but still happy.

       
     
  2. (13)
    1. a.

      進京(V1)趕考(V2)           means-purpose

      jìnjīng__gǎnkǎo

      went-to-the-capital__sitting-a-civil-service-examination

      [He] went to the capital to sit a civil service examination.

       
    2. b.

      生病(V1)住院(V2)了           cause-result

      shēngbìng__zhùyuàn__le

      sick__stay-in-the-hospital__LE

      get sick and stay in the hospital.

       
     
  3. (14)
    1. a.

      偷閒(V1)走(V2)到外面           purpose-means

      tōuxián__zǒudào__wàimiàn

      take-a-break__go-to__outside

      In order to take a break [he] goes outside.

       
    2. b.

      走(V1)到外面偷閒(V2)           means-purpose

      zǒudào__wàimiàn__tōuxián

      go-to__outside__take-a-break

      go outside and take a break.

       

    Using common-sense knowledge, relations are often deduced from the knowledge of entailment, implication, or presupposition between CPCs, as shown in the following examples respectively.

     
  4. (15)

    消失(V1)不見(V2)了           head event-apposition V1 entails V2

    xiāoshī__bújiàn__le

    vanish__disappear__LE

    vanish and disappear

     
  5. (16)

    喝酒(V1)醉倒(V2)          cause-result V2 implies V1

    hējiǔ__zuìdǎo

    drink-alcohol__fall-down-drunkenly

    drink wine and become drunk

     
  6. (17)

    水加熱(V1)到一百度沸騰(V2)           condition-result V2 presupposes V1

    shuǐ__jiārè__dào__yībǎidù__fèiténg

    water__heat-up__to__100-degree__be-boiled

    Heat water up to 100 degrees and it will boil.

     
Clearly, because of the sentential (propositional) logic, we cannot freely reverse the V1-V2 sequence in the above sentences, unless a specific connective occurs to explain how the semantic focus has changed as in the example in (18). There are weak or unobvious entailment relations that exist between certain verbs, which also make for unreasonable reversed orderings as shown in (19). In other cases, the reversed ordering, although not ungrammatical, does cause a shifting of sense, at the same time changing the relation between subevents as shown in (20), that is, the latter event is always considered a purpose.
  1. (18)
    1. a.

      西班牙戰敗(V1)投降(V2)          cause-result

      xībānyá__zhànbài__tóuxiáng

      Spain__be-defeated__surrender

      Spain was defeated and surrendered.

       
    2. b.

      西班牙投降(V1)是因為戰敗(V2)           result-cause

      xībānyá__tóuxiáng__shì__yīnwèi__zhànbài

      Spain__surrender__SHI__because__be-defeated

      Spain surrendered because it was defeated.

       
     
  2. (19)
    1. a.

      桌子收拾(V1)乾淨(V2)           means-purpose

      zhuōzi__shōushi__gānjìng

      table__tidy-up__clean

      Table was tidied up and cleaned.

       
    2. b.

      *桌子乾淨(V1)收拾(V2)

      zhuōzi__gānjìng__shōushi

      table__clean__tidy-up

       
     
  3. (20)
    1. a.

      開門(V1)出去(V2)          means-purpose

      kāimén__chūqù

      open-the-door__go-out

      open the door to go out

       
    2. b.

      出去(V1)開門(V2)           means-purpose

      chūqù__kāimén

      go-out__open-the-door

      go out to open the door

       

    In addition, combinations of specific verbs may be idiomatic and thus seldom reversed, as shown in (21).

     
  4. (21)
    1. a.

      祝你旅行(V1)愉快(V2)          topic-comment

      zhù__nǐ__lǚxíng__yúkuài

      wish__you__travel__happy

      Wishing you happy travels.

       
    2. b.

      *祝你愉快(V1)旅行(V2)

      zhù__nǐ__yúkuài__lǚxíng

      wish__you__happy__travel

       

    More examples are provided to illustrate that context and world knowledge are often necessary for a correct understanding of CPCs. As in (22), 想 xiǎng ‘think’ naturally precedes 回答 huídá ‘reply’ to reflect the process of human mental behavior, and in (23), the sequence of 救 jiù ‘rescue’ and 上岸 shàngàn ‘ashore’ demonstrate the factual process of rescue. In (24), we either infer from the context that one animal is sick so the speaker does not want it, or our common sense tells us that illness makes something undesirable; in either case, a cause-result relation between V1 and V2 is determined.

     
  5. (22)

    他想(V1)了一會回答(V2)我           TimeBefore-TimeAfter

    tā__xiǎng__le__yīhuǐ__huídá__wǒ

    he__think__a-while__answer__me

    He thinks a while and answers me.

     
  6. (23)

    漁人把他救(V1)上岸(V2)           TimeBefore-TimeAfter

    yúrén__bǎ__tā__jiù__shàngàn

    fisherman__BA__he__rescue__get-on-shore

    The fisherman rescues him and gets him on shore.

     
  7. (24)

    這隻早就病(V1)了,換(V2)一隻別的 cause-result

    zhè__zhī__zǎo__jiù__bìng__le,__huàn__yī__zhī__bié__de

    this__CL__early__already__sick__LE,__change__one__CL__other__DE

    This one has long been sick; change to another one.

     

Since our primary concern is about whether the classification system allows users to find a comfortable linking relation between CPCs, and whether different users recognize the same linking relation without difficulty, the immediate goal is to achieve a fairly consistent manual tagging result, which is also an important foundation for the future development of automatic semantic relation identification.

4.2 How to determine a prior relation

Multiple relations may exist between CPCs; there is no ideal classification system that supports a unique interpretation based on world knowledge and the discourse context. That is, the relations shown in Fig. 1 are not mutually exclusive. The following sentence is an example.
  1. (25)

    他回家(V1)看(V2)準決賽了           TimeBefore-TimeAfter ? means-purpose ?

    tā__huíjiā__kàn__zhǔnjuésài__le

    he__go-home__watch__semifinal__LE

    He has gone home to watch the semifinal.

     
There are at least two possible interpretations in (25). One simply denotes the temporal sequence between V1 and V2, while the other denotes the means and purpose relation between V1 and V2 since it is highly likely that “watch the semifinal” is an aim. In order to achieve consistent and correct results for either manual or automatic annotations, we construct a decision tree to determine a prior relation among all possible relations, as given in Fig. 2.
Fig. 2
Fig. 2

Decision tree for relation specification

The decision tree is generated by a complete semantic relation framework given in Fig. 1 and the features mentioned in Section 3.2 as discriminative decision node. In the tree structure, relation types also play roles as discriminative decision node. The most salient relation should be selected at first, and the closer to the bottom, the more inclusive and vague sense the relation linked. The decision tree demonstrates their priorities while determining the major relation. For example, in the sentence of  他在台灣出生(V1)成長(V2) tā zài táiwān chūshēng chéngzhǎng ‘he was born and raised in Taiwan’, we first use realis to determine it is a fact description; since there is no intention within V1 and V2, we look for causality in-between. Lacking causality, we then examine if V1 modifies V2 or if V2 is a result state of V1; disproving them both, we continue to look for a temporal relation between V1 and V2. With a positive answer, we then judge whether they are synchronous; since they are not, the TimeBefore-TimeAfter relation is determined.

Clearly, opinion-type relations are less confusing and most are introduced by connective words. To reveal their relations, Appendix 2 Table 4 shows the relations and their associated markers where only four relation markers associated with ambiguous relations as shown in (26).
  1. (26)
    1. a.
      除非 chúfēi ‘unless’
      1. a1.

        condition(-result)

        除非你同意(V1), 我才會去(V2)

        chúfēi__nǐ__tóngyì,__wǒ__cái__huì__qù

        unless__you__agree,__I__then__will__go

        Unless you agree, then I won’t go.

         
      2. a2.

        condition(-conversion)

        除非有(V1)課本, 不然我不去(V2)上學

        chúfēi__yǒu__kèběn,__bùrán__wǒ__bú__qùshàngxué

        unless__have__textbook,__otherwise__I__NEG__go-to-school

        Unless I have textbooks, otherwise I am not going to school.

         
       
    2. b.
      除/除了 chú/chúle ‘In addition to; except for’
      1. b1.

        restrictive(-addition)

        除了送(V1)花, 他甚至還下跪(V2)

        chúle__sònghuā,__tā__shènzhì__hái__xiàguì

        in-addition-to__give-flower,__he__even__still__kneel-down

        In addition to flowers, he even knelt down.

         
      2. b2.

        except(-head event)

        除了遇到(V1)颱風天, 我們全年無休(V2)

        chúle__yùdào__táifēngtiān,__wǒmen__quánnián__wúxiū

        except-for__encounter__typhoon-day,__we__all-year-round__NEG__rest

        Except for the typhoon day, we open all year round.

         
       
    3. c.
      不管/不論/無論 bùguǎn/búlùn/wúlùn ‘no matter; whether… or…’
      1. c1.

        condition(-result)

        不管誰出來選(V1)都會贏(V2)

        bùguǎn__shéi__chūlái__xuǎn__dōu__huì__yíng

        no-matter__who__come-out__run-the-election__all__will__win

        Whoever runs for election will win.

         
      2. c2.

        or

        不管是走路(V1)、騎車(V2)或搭公車(V3)

        bùguǎn__shì__zǒulù,__qíchē__huò__dāgōngchē

        whether__walk,__take-a-bike__or__take-bus

        Whether on foot, by bike, or by bus

         
       
    4. d.
      ‘and; or; not only…but also’
      1. d1.

        and

        他抽煙(V1)也喝酒(V2)

        tā__chōuyān__yě__hējiǔ

        he__smoke__and__drink-alcohol

        He smokes and drinks.

         
      2. d2.

        or

        你可以學(V1)中文, 也可以學(V2)日文

        nǐ__kěyǐ__xué__zhōngwén,__yě__kěyǐ__xué__rìwén

        you__can__learn__Chinese,__or__can__learn__Japanese

        You can learn Chinese or Japanese.

         
      3. d3.

        (restrictive-)addition

        他不但唱歌(V1), 也跳舞(V2)

        tā__búdàn__chànggē,__yě__tiàowǔ

        he__not-only__sing,__but-also__dance

        He not only sings but also dances.

         
       

    We note that word-pair relation markers are more accurate than single-word markers, since their associated relations are usually definite and unique. For example, the three markers  除了chúle ‘in addition to’, 似乎 sìhū ‘seem’, 也 ‘and’ in (27) can establish five possible relations: except-event, and, or, theme-contrast, and restrictive-addition. However, 除了…也 chúle…yě ‘not only… but also’ which expresses the relation of restrictive-addition is the prior relation, since it is the most definite expression of the semantic relation in (27).

     
  2. (27)

    除了表彰(V1)他在中文文學創作的偉大成就之外, 似乎 也有意(V2)借此彰顯高行健 遭到中共當局迫害           restrictive-addition

    chúle__biǎozhāng__tā__zài__zhōngwén__wénxué__chuàngzuò__de__wěidà__ chéngjiù__zhīwài,__sìhū____yǒuyì__jiècǐ__zhāngxiǎn__gāoxíngjiàn__ zāodào__zhōnggòng__dāngjú__pòhài

    not-only__to__honor__he__in__Chinese__literature__creation__DE__great__achievement__besides__seem__also__have-a-mind-to__by-means-of__highlight__Gao-Xingjian__suffer__Chinese-communist__authority__persecute

    It not only honors his great achievements in Chinese literature, but also seems to be meant to highlight the Chinese authorities’ persecution of Gao Xingjian.

     
When no relation markers are available, we then take the meaning of two consecutive events into account. In addition to referring to the logical deduction in Section 3.1, here, we provide examples showing how we select the best relation. In (28), the preceding sentence of (a) and (b) are the same; as the successive sentence of (a) raises an opposite expectation to the preceding event, a concession-disjunctive is determined. For (b), as the successive sentence implies a supposed result, condition-result is recognized.
  1. (28)
    1. a.

      64歲福田康夫的政策手腕受到(V1)了好評, 如何在緊迫的政局當中得以

      發揮才是(V2)受到矚目的           concession-disjunctive

      liùshísìsuì__fútiánkāngfū__de__zhèngcè__ shǒuwàn__shòudào__le__ hǎopíng__rúhé__zài__jǐnpò__de__zhèngjú__dāngzhōng__déyǐ__fāhuī__ cái__shì__shòudào__zhǔmù__de

      64-year-old__Yasuo-Fukuda__DE__policy__wrist__receive__LE__favorable-comment__how__in__urgent__DE__political-situation__among__to__develope__just__SHI__receive__gaze-at__DE

      64-year-old Yasuo Fukuda’s policy strategies have been well received, but what receives the greatest attention is how he handles this pressing political situation.

       
    2. b.

      64歲福田康夫的政策手腕受到(V1)了好評, 他可能被提名(V2) condition-result

      liùshísìsuì__fútiánkāngfū__de__zhèngcè__shǒuwàn__shòudào__le__hǎopíng__tā__kěnéng__bèi__tímíng

      64-year-old__Yasuo-Fukuda__DE__policy__wrist__receive__LE__favorable-comment__he__may__BEI__nominate

      64-year-old Yasuo Fukuda’s policy strategies have been well received; he may be nominated.

       

    Finally, we note that in semantic relation identification for CPCs, we adopt a two-way linkage to avoid interference between head assignments. In the linking construction of Mandarin, Li and Thompson (1981: 631) identify essentially two kinds of sentence linking: forward linking and backward linking. As with linking elements then, connectives are also divided into two kinds. For example, in (29a), 假如 jiǎrú ‘if’ is a forward-linking element whose function is to signal the dependence of clause 1 on clause 2 to complete its message. However, constituents led by certain connectives always play the same role; thus as 下雨 xiàyǔ ‘rain’ must be a condition when introduced by 假如 jiǎrú ‘if’, it is unnecessary to decide which clause in the text is the main clause or the head verb. In fact, due to the influence of English syntax, we increasingly see sentences like (29b).

     
  2. (29)
    1. a.

      假如下雨(clause 1), 我們就在屋裡吃飯(clause 2)          condition-result

      jiǎrú__xiàyǔ,__wǒmen__jiù__zài__wūlǐ__chīfàn

      if__rain,__we__then__in__house__eat

      If it rains (clause 1), we will eat in the house (clause 2).

       
    2. b.

      我們就在屋裡吃飯(clause 1), 假如下雨(clause 2)           result-condition

      wǒmen__ jiù__zài__wūlǐ__chīfàn,__jiǎrú__xiàyǔ

      we__then__in__house__eat,__if__rain

      We will eat in the house (clause 1), if it rains (clause 2).

       

    We thus propose two-way linkage as opposed to one-way linkage, because it prevents interference between head assignments and focuses on the relation structure of CPCs. For example, in (30a), we need not determine which verb is primary but instead clarify the verbs’ relation and the roles they play.

     
  3. (30)
    1. a.

      他做事(V1)快(V2)           topic-comment

      tā__zuòshì__kuài

      he__work__fast

      He works fast.

       
    2. b.

      他做事(V1)快(V2), 說話也快         topic-comment (semantic focus on topic)

      tā__zuòshì__kuài__shuōhuà__yě__kuài

      he__work__fast__talk__also__fast

      He works fast and talks fast too.

       
    3. c.

      他做事(V1)快(V2), 說話慢           topic-comment (semantic focus on the comment of topic)

      tā__zuòshì,__kuài__shuōhuà__màn

      he__work,__fast__talk__slow

      He works fast and talks slow.

       
     
  4. (31)
    1. a.

      他生病(V1)住院(V2)了          cause-result

      tā__shēngbìng__zhùyuàn__le

      he__sick__stay-in-the-hospital__LE

      He was sick and stayed in the hospital.

       
    2. b.

      他住院(V1)了, 因為生病(V2)           result-cause

      tā__zhùyuàn__le,__yīnwèi__shēngbìng

      he__stay-in-the-hospital,__LE__because-of__sick

      He stayed in the hospital because of sickness.

       

    When a relevant sentence occurs, as it shown in (30b) and (30c), a switch of semantic focus does not change our understanding of the original CPCs. Even when the VP positions change, the relation of the construction does not change, as illustrated in (31), where an unspecified temporal relation holds between the events, allowing for the inversion of the constituents without significant changes in meaning.

     

5 Experiment and discussion

To evaluate the uniqueness and completeness criteria and to understand how well defined our classification system is, we conducted an annotation experiment involving two Chinese undergraduate students without a linguistic background and two second-year graduate students from the linguistic department. They had never participated in any semantic labeling task and were unfamiliar with our classification system. Before labeling, our classification system was explained using 100 examples with answers during a 1-h training course. Annotators were allowed to keep their 100 training examples (not part of the testing data) as references during the experiment. Each annotator was to label both middle-level types and fine-grained subclasses for 100 discourse relations extracted from HIT-CDTB and 100 serial verb relations extracted from Sinica Treebank, and at the same time reveal whether each tag of their selection was based on the decision tree or the connective markers. Since the annotators are tested for the agreement of relation identification, they are told which verb-pair is the analyzed target. The analyzed verb-pair must be on the same parsing level, i.e., the nested structure is not taken into account since verbs occur in nested structure are not regarded as CPCs. At the meanwhile, a reference standard annotation has been set by two proficient annotators with full understanding of our classification and prior labeling procedure. Part of our experimental data is listed in the Appendix 3, Table 5.

Results show an average of 73% of the annotator labels were consistent with the reference standard annotation for middle-level labeling and an average of 69% were consistent with the reference standard annotation for fine-grained subclasses labeling, as shown in Table 1. Compare with the data claimed by current works as cited in Section 2.2, the result confirms that our classification system is promising and is easily understood. Because although the agreement score is 15–20% lower than Zhou and Xue (2012) and Zhou et al. (2014), they only deal with discourse relation and label coarse-grained sense relation. Furthermore, the uniqueness criterion of our classification system is met, since the decision tree leads to the best choice among the potentially ambiguous candidates. In addition, the completeness criterion is met for the decision tree end nodes, that is, elaboration and addition are sufficient to include a broader range of fine-grained minor semantic relations proposed by other systems. All annotators reported that they were able to find a satisfactory annotation for each test problem without difficulty, though they may still have different interpretations.
Table 1

Annotator performance

Labeling grain

Annotator 1

Annotator 2

Annotator 3

Annotator 4

Average

Middle-level

0.715

0.680

0.760

0.780

0.734

Low-level

0.685

0.635

0.695

0.750

0.691

Cohen’s kappa coefficients, a statistic which measures inter-rater agreement for categorical items, are also shown in Table 2.
Table 2

Cohen’s kappa coefficient for middle-level labeling

 

Annotator 2

Annotator 3

Annotator 4

Annotator 5 (reference standard)

Annotator 1

0.59

0.60

0.64

0.67

Annotator 2

 

0.53

0.57

0.64

Annotator 3

  

0.63

0.73

Annotator 4

   

0.76

According to the agreement evaluated by Cohen’s kappa coefficient, all four annotators had scores of 0.61–0.80 with respect to the reference standard, which is interpreted as substantial agreement. As for the comparison between annotators, most of them attained scores of 0.41–0.60 or better, which indicates moderate agreement. This shows that the reference standard is indeed more knowledgably created than the annotator labeling; this suggests more training for annotators to improve their performance. Nevertheless, our main concern is enhancing our classification system for future implementation in automatic semantic role labeling systems. To achieve this goal, we further analyzed the errors for each relation. The average labeling accuracies for all relations are shown in Fig. 3.
Fig. 3
Fig. 3

Accuracies for the 13 middle-level relations

Clearly, synchronous is the most confused relation type for annotators; its error distribution is shown in Fig. 4. We observe that 38% of the replacement errors are caused by the first decision (realis), since the error labels addition, comparison, and attribution are on the other side of decision tree. It seems that we should provide more linguistic cues to discriminate realis and irrealis instead of purely relying on annotator intuition. For example, the markers  同時 tóngshí ‘meanwhile’ and 也 ‘also’ are good indicators for realis and synchronous. Also, annotators often used elaboration instead of synchronous because they were not aware of the temporal relation that exists between serial events such as 等船(V1)休憩(V2) děng chuán xiūqì ‘wait for the boat (V1) coming and take a rest (V2)’ or 歡呼(V1)雀躍(V2) huānhū quèyuè ‘cheering (V1) and jumping (V2)’. However, as we have mentioned, elaboration is allowed to have a broader interpretation and elaboration and synchronous are not complementary; thus, we may consider relaxing our standard to accommodate this, i.e., if annotators pick the near nodes of addition or elaboration, we should consider them agree to each other.
Fig. 4
Fig. 4

Error distribution of synchronous

As another example, take background, the label with the second-worst accuracy. As shown in Fig. 5, the relation most confused with background is evaluation, because we classify the phrase pattern “V+result”—such as for 發展(V1)得很好(V2) fāzhǎn de hěnhǎo ‘well-developed’—as background. However, most annotators label this as topic-comment under evaluation, or as elaboration which denotes two realis events without a specific relation. This high incidence of mislabeling led us to consider disregarding “V+result” as a background relation and place evaluation nodes on both realis and irrealis sides of the decision tree since either realis or irrealis V1 could occur in sentences with evaluation constructions. As for the uncertainty between background and purpose, it is an uncertainty about intention. For example, in the sentence of 張大(V1)眼睛看(V2) zhāngdà yǎnjing kān ‘open eyes to look’, we use “to” to link V1 and V2 in English, implying an existing intention. However, in Chinese, there is no such marker indicating intention and we tend to regard V1 as a manner—either dynamic or static—to achieve V2. Actually, we adopt 著 zhe as a manner marker; thus, when the phrase pattern “V1 著 zhe V2” occurs, V1 is forced to be a background of V2. Similarly, if 張大著眼睛看 zhāngdà zhe yǎnjing kān ‘open ZHE eyes look’ is a legal sentence that means V1 is better as a background of V2. Therefore, again, this indicates that other than world knowledge, linguistic cues are important features to determine semantic relations for CPCs.
Fig. 5
Fig. 5

Error distribution of background

Connective markers are useful cues for annotators to decide relations. Table 3 shows the annotator labeling basis: 58% of the selections for discourses are based on the connective markers provided in Appendix 2, Table 4. For SVCs, in contrast, because in Chinese we rarely use connective markers to link two serial verbs in a single sentence, only 14% of the selections are based on the provided markers. Hence, annotators reported that relation within a single sentence is more difficult to label than relation within a discourse. To resolve this problem, in the future, we may ask annotators to decide the semantic relation for CPCs without relation markers by adding appropriate conjunctive markers for help.
Table 3

Labeling basis distribution

Labeling basis

Annotator 1

Annotator 2

Annotator 3

Annotator 4

Distribution of labeling basis

Discourse relation

Decision-tree

59

40

29

40

0.42

Marker

41

60

71

60

0.58

SVCs relation

Decision-tree

87

91

79

87

0.86

Marker

13

9

21

13

0.14

In summary, we propose six ways to improve our classification and labeling system. The first is that according to the kappa coefficient, the more training provided to our annotators, the more agreement we can expect. The second is to extract more connective markers and linguistic cues from real-world text and add these into the checklist for reference. The third is that since addition and elaboration are broader relation types, we should consider relaxing our standard for their near node on the decision tree given more experimental evidence showing this need. The fourth is to consider the evaluation relation for both realis and irrealis subtrees. The fifth is to train annotators to test the relation type by fabricating connective markers. The sixth is to have annotators follow the decision tree step-by-step, that is, not allow annotators to neglect higher-level decisions and jump to latter choices.

6 Conclusion

Mandarin Chinese imposes weaker restrictions on the semantic properties of CPCs and thus makes no clear distinction between them. To determine a proper semantic relation between CPCs, we slightly modify our classification scheme by adding an evaluation node on the realis side of the decision tree. The final classification system has 14 middle-level relations and 24 fine-grained relations arranged in a decision tree with discriminative features—realis, intention, causality, and so on—to reveal the priority order among possible relations, as shown in Figs. 6 and 7. The decision tree induction and broader relation types meet the uniqueness and completeness criteria. Since in serial verb construction and discourse construction we observe the same difficulty in recognizing semantic relations between serial events, we adopt a broad sense of CPCs to include the different syntactic structures commonly used in Chinese languages to express a complex event which shares an identical topic. This definition of CPCs is novel but logical and practical. And comparing the annotation result with Huang and Chen (2011) and Zhou et al. (2014) cited in Section 2.2, our labeling distribution is much more balanced as shown in Fig. 8.
Fig. 6
Fig. 6

Revised relations between CPCs

Fig. 7
Fig. 7

Revised decision tree for relation specification

Fig. 8
Fig. 8

Distribution of relation annotation

The factors that influence the deduction of relation recognition are sense of events, markers, event ordering, and knowledge-based reasoning. The decision tree assistance in identifying a proper relation is based on event ordering and knowledge reasoning. In practice, however, labeling still depends heavily on human judgment. In order to clarify how well defined our classification system is, we conducted an experiment which shows an average of 73% accuracy and an approximate 70% agreement by Cohen’s kappa coefficient in middle-level labeling which indicates substantial agreement. We analyzed the error type for each relation and summarized six ways to improve our classification and labeling system, which is predicted to enhance the agreement by Cohen’s kappa up to 0.81–1.00, that is, almost perfect agreement in the future.

As a final remark, the proposed classification system is designed by following our proposed methodology. It results in a succinct semantic relation identification system for Chinese CPCs incorporated with a hierarchical decision tree to meet the uniqueness and completeness criteria of semantic relation recognition and which is in contrast to the conventional complex classification schemes discussed in Section 2.

Declarations

Acknowledgements

We thank the anonymous reviewers for their very helpful suggestions and criticisms.

Authors’ contributions

All authors read and approved the final manuscript.

Competing interests

The authors declare that they have no competing interests.

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Authors’ Affiliations

(1)
Research Center for Translation, Compilation and Language Education, National Academy for Educational Research, New Taipei City, Taiwan
(2)
Institute of Information Science, Academia Sinica, Taipei, Taiwan

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© The Author(s). 2017

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