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Empirical studies of text coherence often use tree-like structures in the spirit of Rhetorical Structure Theory (RST) as representational device. This paper identifies several sources of ambiguity in RST-inspired trees and argues that such structures are therefore not as explanatory as a text representation should be. As an alternative, an approach toward multi-level annotation (MLA) of texts is proposed, which separates the information into distinct levels of representation, in particular: referential structure, thematic structure, conjunctive relations, and intentional structure. Levels are conceptually built upon each other, and human annotators can produce them using a dedicated software environment. We argue that the resulting multi-level corpora are descriptively more adequate, and as a resource are more useful than RST-style treebanks.
We present a general framework for integrating annotations from different tools and tag sets. When annotating corpora at multiple linguistic levels, annotators may use different expert tools for different phenomena or types of annotation. These tools employ different data models and accompanying approaches to visualization, and they produce different output formats. For the purposes of uniformly processing these outputs, we developed a pivot format called PAULA, along with converters to and from tool formats. Different annotations are not only integrated at the level of data format, but are also joined on the level of conceptual representation. For this purpose, we introduce OLiA, an ontology of linguistic annotations that mediates between alternative tag sets that cover the same class of linguistic phenomena. All components are integrated in the linguistic information system ANNIS : Annotation tool output is converted to the pivot format PAULA and read into a database where the data can be visualized, queried, and evaluated across multiple layers. For cross-tag set querying and statistical evaluation, ANNIS uses the ontology of linguistic annotations. Finally, ANNIS is also tied to a machine learning component for semiautomatic annotation.