{ "paper_id": "W90-0117", "header": { "generated_with": "S2ORC 1.0.0", "date_generated": "2023-01-19T04:00:18.984725Z" }, "title": "Parsimonious and Profligate Approaches to the Question of Discourse Structure Relations", "authors": [ { "first": "Eduard", "middle": [ "H" ], "last": "Hovy", "suffix": "", "affiliation": { "laboratory": "", "institution": "Information Sciences Institute of USC", "location": { "addrLine": "4676 Admiralty Way Marina del Rey", "postCode": "90292-6695", "region": "CA" } }, "email": "" } ], "year": "", "venue": null, "identifiers": {}, "abstract": "To computationalists investigating the structure of coherent discourse, the following questions have become increasingly important over the past few years: Can one describe the structure of discourse using interclausal relations? If so, what interclausal relations are there? How many are required? A fair amount of controversy exists, ranging from the parsimonious position (that two intentional relations suffice) to the profligate position (that an open-ended set of semantic/rhetorical relations is required). This paper outlines the arguments and then summarizes a survey of the conclusions of approximately 25 researchers-from linguists to computational linguists to philosophers to Artificial Intelligence workers. It classifies the more than 350 relations they have proposed into a hierarchy of increasingly semantic relations, and argues that though the hierarchy is open-ended in one dimension, it is bounded in the other and therefore does not give rise to anarchy. Evidence for the hierarchy is mentioned, and its relations (which are rhetorical and semantic in nature) are shown to be complementary to the two intentional relations proposed by the parsimonious position.", "pdf_parse": { "paper_id": "W90-0117", "_pdf_hash": "", "abstract": [ { "text": "To computationalists investigating the structure of coherent discourse, the following questions have become increasingly important over the past few years: Can one describe the structure of discourse using interclausal relations? If so, what interclausal relations are there? How many are required? A fair amount of controversy exists, ranging from the parsimonious position (that two intentional relations suffice) to the profligate position (that an open-ended set of semantic/rhetorical relations is required). This paper outlines the arguments and then summarizes a survey of the conclusions of approximately 25 researchers-from linguists to computational linguists to philosophers to Artificial Intelligence workers. It classifies the more than 350 relations they have proposed into a hierarchy of increasingly semantic relations, and argues that though the hierarchy is open-ended in one dimension, it is bounded in the other and therefore does not give rise to anarchy. Evidence for the hierarchy is mentioned, and its relations (which are rhetorical and semantic in nature) are shown to be complementary to the two intentional relations proposed by the parsimonious position.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Abstract", "sec_num": null } ], "body_text": [ { "text": "This paper proposes an answer to an issue that keeps surfacing in the computational study of the nature of multisentential discourse.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "How Many Interclausal Discourse Coherence Relations?", "sec_num": null }, { "text": "It has been argued fairly generally that multisentence texts (specifically, short texts such *This work was supported by the Rome Air Development Center under RADC contract FQ7619-89-03326-0001. as paragraphs) are coherent by virtue of the rhetorical or semantic relationships that hold among individual clauses or groups of clauses (see, for example, [Aristotle 54, Hobbs 79, Grimes 75, Mann & Thompson 88] . In this view, a text is only coherent when the speaker aids the heater's inferential understanding processes by providing clues, during the discourse, as to how the pieces of the text interrelate. Such clues are often cue words and phrases such as \"in order to\" (signalling a purpose for an action) or \"then\" (signalling the next entity in some temporal or spatial sequence); but they can also be shifts in tense and mode (such as in \"She was gone. Had she been there, all would have been well\"), and even appropriate pronominalizations.", "cite_spans": [ { "start": 352, "end": 366, "text": "[Aristotle 54,", "ref_id": null }, { "start": 367, "end": 376, "text": "Hobbs 79,", "ref_id": null }, { "start": 377, "end": 387, "text": "Grimes 75,", "ref_id": null }, { "start": 388, "end": 407, "text": "Mann & Thompson 88]", "ref_id": null } ], "ref_spans": [], "eq_spans": [], "section": "How Many Interclausal Discourse Coherence Relations?", "sec_num": null }, { "text": "Various researchers in various intellectual subfields have produced lists of such relations for English. Typically, their lists contain between seven and thirty relations, though the more detailed the work (which frequently means the closer the work is to actual computer implementation), the more relations tend to be named.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "How Many Interclausal Discourse Coherence Relations?", "sec_num": null }, { "text": "I have collected the lists of over 25 researchers --from philosophers (e.g., [Toulmin 58] ) to linguists (e.g., [Quirk & Greenbaum 73, Halliday 85] ) to computational linguists (e.g., [Mann & Thompson 88, Hobbs 79] ) to Artificial Intelligence researchers (e.g., [Schank & Abelson 77, Moore & Paris 89, Dahlgren 88 ]) --amounting to a total of more than 350 relations. The researchers and their lists appear below.", "cite_spans": [ { "start": 77, "end": 89, "text": "[Toulmin 58]", "ref_id": null }, { "start": 112, "end": 134, "text": "[Quirk & Greenbaum 73,", "ref_id": null }, { "start": 135, "end": 147, "text": "Halliday 85]", "ref_id": null }, { "start": 184, "end": 204, "text": "[Mann & Thompson 88,", "ref_id": null }, { "start": 205, "end": 214, "text": "Hobbs 79]", "ref_id": null }, { "start": 263, "end": 284, "text": "[Schank & Abelson 77,", "ref_id": null }, { "start": 285, "end": 302, "text": "Moore & Paris 89,", "ref_id": null }, { "start": 303, "end": 314, "text": "Dahlgren 88", "ref_id": null } ], "ref_spans": [], "eq_spans": [], "section": "How Many Interclausal Discourse Coherence Relations?", "sec_num": null }, { "text": "In this paper, I will call the assumption of these researchers, namely that some tens of interclausal relations are required to describe the structure of English discourse, the Profligate Position.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "How Many Interclausal Discourse Coherence Relations?", "sec_num": null }, { "text": "Unfortunately, the matter of interclausal relations is not simple, and not everyone agrees with this position. These relations are seldom explicitly signalled in the text, and even when they are, they seem to take various forms particular to their use in context. This fact has led some researchers, notably [Grosz & Sidner 86] , to question the wisdom of identifying a specific set of such relations. They argue that trying to identify the \"correct\" set is a doomed enterprise, because there is no closed set; the closer you examine interclausal relationships, the more variability you encounter, until you find yourself on the slippery slope toward the full complexity of semantics proper. Thus though they do not disagree with the idea of relationships between adjacent clauses and blocks of clauses to provide meaning and to enforce coherence, they object to the notion that some small set of interclausal relations can describe English discourse adequately.", "cite_spans": [ { "start": 308, "end": 327, "text": "[Grosz & Sidner 86]", "ref_id": null } ], "ref_spans": [], "eq_spans": [], "section": "How Many Interclausal Discourse Coherence Relations?", "sec_num": null }, { "text": "As a counterproposal, Grosz and Sidner sidestep the issue of the structure of discourse imposed by semantics and define two very basic relations, DOMINANCE and SATISFACTION-PRECEDENCE, which carry purely intentional (that is, goal-oriented, plan-based) import. They use these relations in their theory of the structure of discourse, according to which some pieces of the text are either subordinate to or on the same level as other pieces, with respect to the interlocutors' intentions. I will call this position, namely that two interclausal relations suffice to represent discourse structure, the Parsimonious Position.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "How Many Interclausal Discourse Coherence Relations?", "sec_num": null }, { "text": "From the point of view of text analysis, the Parsimonious approach seems satisfactory. Certainly one can analyze discourse using the two intentional relations. However, from the point of view of text generation, this approach is not sufficient. Practical experience has shown that text planners cannot get by on intentional considerations alone, but need considerably more rhetorical and semantic information in order to construct coherent text (there are many examples; see [McKeown 85, Hovy 88a, Moore & Swartout 88, Paris 88, Rankin 89, Cawsey 89] ). In practical terms, this means that text planning systems require a rich library of interclausal relations.", "cite_spans": [ { "start": 475, "end": 487, "text": "[McKeown 85,", "ref_id": null }, { "start": 488, "end": 497, "text": "Hovy 88a,", "ref_id": null }, { "start": 498, "end": 518, "text": "Moore & Swartout 88,", "ref_id": null }, { "start": 519, "end": 528, "text": "Paris 88,", "ref_id": null }, { "start": 529, "end": 539, "text": "Rankin 89,", "ref_id": null }, { "start": 540, "end": 550, "text": "Cawsey 89]", "ref_id": null } ], "ref_spans": [], "eq_spans": [], "section": "How Many Interclausal Discourse Coherence Relations?", "sec_num": null }, { "text": "\u2022 Does one really need semantic and/or rhetorical discourse structure relations?", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Questions such as", "sec_num": null }, { "text": "\u2022 Just how many such relations are there?", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Questions such as", "sec_num": null }, { "text": "\u2022 What is their nature? How do they relate to the two intentional relations?", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Questions such as", "sec_num": null }, { "text": "will not go away. Until it is resolved to the satisfaction of the adherents both positions, further work on text planning and discourse analysis is liable to continue getting stranded on the rocks of misunderstanding and disagreement. This paper suggests a compromise that hopefully opens up the way for further development.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Questions such as", "sec_num": null }, { "text": "How can one reconcile the two sides? That is to say, how can one build a library of interclausal relations that are simultaneously expressive enough to satisfy the requirements of text planning systems but do not simply form an unbounded ad hoc collection of semantic relations with no regard to the intentional ones?", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "An Unsatisfactory Solution", "sec_num": null }, { "text": "One answer is to produce a two-dimensional organization of relations, with one dimension constrained in the number of relations and the other unconstrained (and increasingly semantic in nature; see Objection 1 below). Such organization is a hierarchic taxonomy of limited width but of unbounded depth; the more general a relation is, the higher it is in the hierarchy and the fewer siblings it has.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "An Unsatisfactory Solution", "sec_num": null }, { "text": "An appealing hierarchy is shown in Figure 1 . It displays a number of very desirable features. In particular, the top few levels are strictly bounded: no logical alternatives to ASYMMETRIC and SYM-METRIC exist, and one level lower, under ASYM-METRIC, following Grosz and Sidner there is no need to use any other relation than DOMINATES and SATISFACTIONPRECEDES at that level. Increasingly detailed relations appear at lower levels, which (as is discussed below) remain relatively bounded. Still, the more one specifies a particular relation to distinguish it from others, the more semantic it necessarily becomes (since increasing specification invariably introduces additional semantic features; that is the nature of the specialization process), and the lower it appears in the hierarchy. Though one does eventually approach the full complexity of semantics proper, the approach is not unprincipled; each relation is always constrained by its position in the hierarchy and inherits much of its structural and other features from its ancestors.", "cite_spans": [], "ref_spans": [ { "start": 35, "end": 43, "text": "Figure 1", "ref_id": null } ], "eq_spans": [], "section": "An Unsatisfactory Solution", "sec_num": null }, { "text": "In this scheme, one can (and the Parsimonious do) perform discourse analysis and study discourse structure wholly at the level of DOMINATES and SATISFACTIONPRECEDES, and never come into conflict with the structural descriptions found empirically by the Profligate. One is simply not being as specific about the particular interclausal relations that make up the discourse.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "An Unsatisfactory Solution", "sec_num": null }, { "text": "However, this taxonomy is unsatisfactory. It is impossible in practise to place into the hierarchy with certainty most of the relations found necessary by the Profligate. For example, the relation CAusE (of various kinds) is one of the most agreed-upon relations. But is it to be classified as a type of DOM-INATES or of SATISFACTIONPRECEDES? Though it seems able to function either way, this question is impossible to answer, since none of the concepts involved are clearly enough defined (certainly nobody has provided a general definition of CAUSE -how could one?; it has been the topic of centuries of philosophical debate. And even the limited definition required for the purposes of Computational Linguistics in a particular application domain with a given ontology of terms has not been provided satisfactorily yet).", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "An Unsatisfactory Solution", "sec_num": null }, { "text": "The answer to the dilemma: It is a mistake to classify rhetorical and semantic relations under the relations DOMINATES and SATISFACTIONPRECEDES. This insight does not destroy the hierarchy; most of its desirable properties are maintained. It does mean, however, that a new top-level organization must be found and that the role of intentional relations vis \u00a3 vis rhetorical/semantic relations must be explained. I address the first point here, and the role of the intentional relations later on.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "A Better Solution", "sec_num": null }, { "text": "I have not found any highly compelling top-level organization. Ideally, the top level should partition the relations into a few (say, three or four) major groups that share some rhetorical or semantic property. In the absence of a more compelling suggestion (for which I continue to search), I use here the top-level trifurcation of [Halliday 85] , which is based, roughly speaking, on the \"semantic distance\" between the contents of the two clauses. The three relations are ELABORATION, ENHANCE-MENT, and EXTENSION. ELABORATION relations hold between entities and their immediate constituents or properties, and have a definitional flavor; ENHANCEMENT relations hold between entities and their circumstances of place, time, manner, etc.; and EXTENSION relations hold between entities and more distant entities such as causes, followups, contrasts, etc. Halliday's classification has been modified and regularized by Matthiessen (per-sonM communication). For want of compelling arguments to the contrary, I use Matthiessen's modification of I-Ialliday's ideas as the basis for the top level of the hierarchy.", "cite_spans": [ { "start": 333, "end": 346, "text": "[Halliday 85]", "ref_id": null } ], "ref_spans": [], "eq_spans": [], "section": "A Better Solution", "sec_num": null }, { "text": "In order to construct the hierarchy, I collected over 350 relations from 26 researchers in various fields. I merged the relations, coming up with a set of 16 on the second tier of the hierarchy, and then classified more particular subrelations where appropriate. The hierarchy of interclausal relations is given in Figure 2 AbstractInstance 13Interpretation (2)--Evaluation 3S-mmary (4) Restatement (9)/Conclusion 7_Location (6) . ~Time (7)", "cite_spans": [], "ref_spans": [ { "start": 315, "end": 323, "text": "Figure 2", "ref_id": null } ], "eq_spans": [], "section": "A Better Solution", "sec_num": null }, { "text": "Circumstance (4)E=---Means (4) / ~ Manner (2) / ~Instrument (1) Enhancement ~Background (4) (3) (1)~ ParallelEvent ~Solutionhood (1),,, Answer (1) SeqTemporal (6) Sequence (6)IIIAsymmetricSymmetricIIIIIIDominatesSatisfactionPrecedesComparativeLoEicalRelationIIII-Circumstance-Sequence-Contrast-Conjunction-Elaboration-Restatement-Comparison-Disjunction-etc.-etc.-etc.-etc.", "num": null, "text": "An Unsatisfactory Attempt at Hierarchicalizing Interclausal Relations. ........................", "html": null, "type_str": "table" }, "TABREF3": { "content": "
(that is, asymmetrical and symmetrical relation-
ships:
HYPO: Joe left because Sue worked (5
Sue worked because Joe left)
PARA:He shouted when the horse
jumped (= the horse jumped when he
shouted)
respectively). But this does not work because both
DOMINATES and SATISFACTIONPRECEDES are by
their natures asymmetrical. Another possible gen-
eralization is to use the two syntactic relations
MULTIVARIATE and UNIVARIATE (that is, contain-
ing an embedded syntactic type recursion (a gram-
matical rank shift) ornot, as in:
MULTI: Sue's working caused [Joe to
leave] (S embedded in S)
UNI: Joe left because Sue worked (two
coequal Ss)
", "num": null, "text": "However, it is not clear how to generalize DOMI-NATES and SATISFACTIONPRECEDES to cover such cases as well. One possible generalization is to use the general relations HYPOTAXIS and PARATAXIS", "html": null, "type_str": "table" } } } }