A computational approach to topic and focus in a production model

The aim of the presenteA rc~:~ffeh is the dt~velop ~:~-~i: ~f a lh~gaisdc mo.del of the function01 cont~pts topic and ~i;, m~ ~h:.~: cm~. h<: n~tl in naiurat lmtgnage processing systems. Tk~ ?a[~r d~'.,als wilti two points of' investigation: the first point c~mtx~r~m the identification of the topic and focus of 9at utterauce. Withha the frame of the linguistic discussion on such concepts topic and focus will lye considered as semantic, wagmatic and i.*~tonational rather then as syntactic phenomena. An operational definition of topic a~M tbeus is obtained on the basis of basic semantic-pragmatic categories which are defined in relation to a specitied co~4~zto The second l~int eonoerns the. integration of the topic an6 ibcus identification rules iu a system for natural im,gitage gencratiou. The aim of the application is the validation of the developed topic and focus model with respect to some asl~et of" the generation process like thematic progression and acc~:;nt mapping. Moreover the identification of topic and focus :~an be used to ma~e prediction about the thematic progression ~md ii~ accx:n~ mapping in the blocks world texts. For the predie-~i(>~ of i~definite pronouns like "one" and of definite articles • :,'iddn a noml phrase it is ne¢,ssary to recur to the seman-neA, which "allows speaking about the assumptious of the speaker about the hearer and his world. In fhct in the experiment the slmaker aud the hearer do not see each other; they mainly rely on assumptions about their mutual knowledge /Sehiffers 1972/. Statements of l~e a'e for ex. sink(at) where arakis a property symbol of I, and a~ is the statement on(b~,b~.), amk(on(b~,b2)) means that it is assumed to be mutuM lmowledge that the block b t is on the block b> Other examples of statements of L~ are id(b~) meaning that the block b I has been identified in a TAKE action, neq(TAKE) meaning that TAKE can be inte~preteal unequivocally arid apl(li) meaning that li is assumed to be a potential position tbr the moved blocks. For practical reasons we consider the context C to be, a pair of eaets of statements in rite language Iq: . CO~ contains statements about the world of the speaker and those assumptions about mutual knowledge which remain unchanged during an experiment. CO~ contains the SlXmker's assumptions almut the heatvr's blocks, their actual and their pNential positions. ' ~' :a~c in~p<n't~mc,~ of co~xtua| fhctors tbr the whole …