Automatic discourse structure generation using rhetorical structure theory

This thesis addresses a difficult problem in text processing: creating a System to automatically derive rhetorical structures of text. Although the rhetorical structure has proven to be useful in many fields of text processing such as text summarisation and information extraction, Systems that automatically generate rhetorical structures with high accuracy are difficult to find. This is because discourse is one of the biggest and yet least well defined areas in linguistics. An agreement amongst researchers on the best method for analysing the rhetorical structure of text has not been found. This thesis focuses on investigating a method to generate the rhetorical structures of text. By exploiting different cohesive devices, it proposes a method to recognise rhetorical relations between spans by checking for the appearance of these devices. These factors include cue phrases, noun-phrase cues, verb-phrase cues, reference words, time references, substitution words, ellipses, and syntactic information. The discourse analyser is divided into two levels: sentence-level and text-level. The former uses syntactic information and cue phrases to segment sentences into elementary discourse units and to generate a rhetorical structure for each sentence. The latter derives rhetorical relations between large spans and then replaces each sentence by its corresponding rhetorical structure to produce the rhetorical structure of text. The rhetorical structure at the text-level is derived by selecting rhetorical relations to connect adjacent and non-overlapping spans to form a discourse structure that covers the entire text. Constraints of textual organisation and textual adjacency are effectively used in a beam search to reduce the search space in generating such rhetorical structures. Experiments carried out in this research received 89.4% F-score for the discourse segmentation, 52.4% F-score for the sentence-level discourse analyser and 38.1% F-score for the final output of the System. It shows that this approach provides good performance comparison with current research in discourse

On counting AC(0) circuits with negative constants

. Continuing the study of the relationship between TC 0 , AC 0 and arithmetic circuits, started by Agrawal et al. [1], we answer a few questions left open in this paper. Our main result is that the classes DiffAC 0 and GapAC 0 coincide, under poly-time, log-space, and log-time uniformity. From that we can derive that under logspace uniformity, the following equalities hold: C=AC 0 = PAC 0 = TC 0 : 1 Introduction The study of counting complexity classes was started by the pioneering work of Valiant [16] on the class #P . It consists of functions which associate to a string x the number of accepting computations of an NP-machine on x. A wellknown complete problem for this class is the computing of the permanent of an integer matrix. The class #L was defined later analogously with respect to NL-computation [3, 18, 14]. Each of these classes can be defined equivalently either by counting the number of accepting subtrees of the corresponding class of uniform circuits, o..

Small heat shock proteins prevent aggregation of citrate synthase and bind to the N-terminal region which is absent in thermostable forms of citrate synthase

Item does not contain fulltex