We describe a computational model for planning phrases like “more than a quarter” and “25.9 per cent” which describe proportions at different levels of precision. The model lays out the key choices in planning a numerical description, using formal definitions of mathematical form (e.g., the distinction between fractions and percentages) and roundness adapted from earlier studies. The task is modeled as a constraint satisfaction problem, with solutions subsequently ranked by preferences (e.g., for roundness). Detailed constraints are based on a corpus of numerical expressions collected in the NumGen project, 1 1 NumGen: Generating intelligent descriptions of numerical quantities for people with different levels of numeracy ( http://mcs.open.ac.uk/sw6629/numgen ). NumGen was funded by the Economic and Social Research Council under Grant Ref. RES-000-22-2760. and evaluated through empirical studies in which subjects were asked to produce (or complete) numerical expressions in specified contexts.

This article describes a method for composing fluent and complex natural language questions, while avoiding the standard pitfalls of free text queries. The method, based on Conceptual Authoring, is targeted at question-answering systems where reliability and transparency are critical, and where users cannot be expected to undergo extensive training in question composition. This scenario is found in most corporate domains, especially in applications that are risk-averse. We present a proof-of-concept system we have developed: a question-answering interface to a large repository of medical histories in the area of cancer. We show that the method allows users to successfully and reliably compose complex queries with minimal training.

This article describes an implemented system which uses centering theory for planning of coherent texts and choice of referring expressions. We argue that text and sentence planning need to be driven in part by the goal of maintaining referential continuity and thereby facilitating pronoun resolution: Obtaining a favorable ordering of clauses, and of arguments within clauses, is likely to increase opportunities for nonambiguous pronoun use. Centering theory provides the basis for such an integrated approach. Generating coherent texts according to centering theory is treated as a constraint satisfaction problem. The well-known Rule 2 of centering theory is reformulated in terms of a set of constraints—cohesion, salience, cheapness, and continuity—and we show sample outputs obtained under a particular weighting of these constraints. This framework facilitates detailed research into evaluation metrics and will therefore provide a productive research tool in addition to the immediate practical benefit of improving the fluency and readability of generated texts. The technique is generally applicable to natural language generation systems, which perform hierarchical text structuring based on a theory of coherence relations with certain additional assumptions.

We argue the case for abstract document structure as a separate descriptive level in the analysis and generation of written texts. The purpose of this representation is to mediate between the message of a text (i.e., its discourse structure) and its physical presentation (i.e., its organization into graphical constituents like sections, paragraphs, sentences, bulleted lists, figures, and footnotes). Abstract document structure can be seen as an extension of Nunberg's “text-grammar” it is also closely related to “logical” markup in languages like HTML and LaTEX. We show that by using this intermediate representation, several subtasks in language generation and language understanding can be defined more cleanly.

This paper starts by introducing a class of future document authoring systems that will allow authors to specify the content and form of a text+pictures document at a high level of abstraction, while leaving responsibility for linguistic and graphical details to the system. Next, we describe two working prototypes that implement parts of this functionality, based on semantic modeling of the pictures and the text of the document; one of these two, the ILLUSTRATE prototype, is a multimedia extension of previous text authoring systems in the What You See Is What You Meant (WYSIWYM) tradition. The paper concludes with an exploration of the ways in which Multimedia WYSIWYM can be further enhanced, allowing it to approximate the ‘ideal’ systems that were sketched earlier in the paper. Applications of Multimedia WYSIWYM to general-purpose picture retrieval (in the context of the Semantic Web, for example) are also discussed.

The RAGS proposals for generic specification of NLG systems includes a detailed account of data representation, but only an outline view of processing aspects. In this paper we introduce a modular processing architecture with a concrete implementation which aims to meet the RAGS goals of transparency and reusability. We illustrate the model with the RICHES system -- a generation system built from simple linguistically-motivated modules.

Scott and Souza (1990) have posed the problem of how a rhetorical structure (in which propositions are linked by rhetorical relations, but not yet arranged in a linear order) can be realized by a text structure (in which propositions are ordered and linked up by appropriate discourse connectives). Almost all work on this problem assumes, implicitly or explicitly, that this mapping is governed by a constraint on compatibility of structure. We show how this constraint can be stated precisely, and present some counterexamples which seem acceptable even though they violate compatibility. The examples are based on a phenomenon we call extraposition, in which complex embedded constituents of a rhetorical structure are extracted and realized separately.

This paper describes an implemented system which uses centering theory for planning of coherent texts and choice of referring expressions. We argue that text and sentence planning need to be driven in part by the goal of maintaining referential continuity and thereby facilitating pronoun resolution: obtaining a favourable ordering of clauses, and of arguments within clauses, is likely to increase opportunities for non-ambiguous pronoun use. Centering theory provides the basis for such an integrated approach. Generating coherent texts according to centering theory is treated as a constraint satisfaction problem.