On Text Coherence Parsing

ON TEXT COHERENCE PARSING Udo llahn Albert-Ludwigs 4hfiversit~t Fmiburg Linguistische Infonnatik / Computerlinguistik Fricdrichstr. 50 D-W-78(X) Freibtn-g i. Bixg, Gcnn;my email: hahn@supreme.coling,uni~freiburg.de ABSTRACT In this paper global patterns of thematic text organization me considered within the framework of a distributed model of text understmlding, ttased on file parsing resuhs of prior lext cohe- sioll analysis, specialized text grammar modules deternfine whether SOllle well-defined text lllltCro organization palteln is cOlll])ulabte flOlll the available text representatiolt SIrUCttlreS. The model underlying text coherence parsing formalizes hither to entirely intuitive textlinguistic notions whose origin can be traced back to Danes's work on thematic progression patleHlS. 1 INTRODUCTION l)ufing tim last years it has become increasingly appar- ent that dialog and text understanding systems must account Ior connectivity relations that extend over sen- tence boundaries. This has led tn a bulk of work deal- ing with varinus forms of cohesimt-preserving lan- guage mechanisms, lnainly in the field of anaphora, which contribute to connectivity among sentences. From the focus on these linguistic phenomena one might obtain a misleading picture of textual connectiv- ity, viz. one that considers it basically as a 'fiat', con- tinuous streanl of formally connected utterances lacking additional structure. Far less research has been devnted to the intemM organization of cohesive utteranccs by mechanisms at a more global level of dialog/text archi- tecture, the level of text coherence. Major computational approaches rclated to co-. herence aspects within a dialog processing framework am due to Reichman's [1978], McKcown's [19851 and Scha & Polmlyi's [19881 lbnnalizations of diatog gram- mars. Coherence criteria of written texts llavc [)cell ill- vestigated ill tile context of 'Rhetorical Stmcttlm Thet) ry' IMann & Thompson 19881 and related extensions le.g., Altemlan 1982, Tucker, Nirenburg & Raskin 19861 of tile original theory of coherence relations ill discom.'se [Hobbs 1982]. A second major methodok)gy which deals with the global stnactufing of written texts is the model nf text lnacro propositions and superstnlc- turns [Kintsch & wm Dijk 1978, van Dijk 19801, tilt latter sharing all relevant pmtxmies one generally altriD- utes to story grammars [Runlelhari 19']51. The problem with this kind of methodology is that, unlike the coher- ence relation approach, the grammat,'s which have been proposed so far are litirly idiosyncnttic 10r each applica- tion dmnain (narratives, weather reports, etc.). Corn- molt to all these approaches is the requirement of a deep, propositionally guided understanding of the un- derlying discourse; in particular, a complete theory o1' its dontain and an exhaustive specifieatitm of a natural language grammar must be supplied in order to guaraw tee proper operation of implemented systelns. This AcqEs In! COL1NG-92, NANI[.:S. 23-28 aot~q' 1992 2 5; might explain wily, with only low exceptions, these UItK|C1S Of text coherence have resisted lullher coral)ilia li0nal treatment as evidenced by Ol)cratiooal systems. We here make an alternative alld conlpt|tationa[ly more tractable l)rolx)sal on how it) deal wifll global text structures at the text coherei1ce level. Its roots Call be traced back to the seminal wolk of F, l)mms [ 1974], …

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