armin@csri.toronto.edu (Armin Haken) (03/23/88)
AI Seminar: 2PM, Tuesday March 29, Sandford Fleming 1105
PLANNING COHERENT MULTISENTENTIAL TEXT
Eduard Hovy
Information Sciences Institute of USC
4676 Admiralty Way
Marina del Rey, CA 90282-6695
Generating multisentential text is hard. Though most text generators
are capable of simply stringing together more than one sentence, they
cannot determine coherent order. Very few programs attempt to plan
out the structure of multisentential paragraphs.
Clearly, the key notion is coherence. The reason some paragraphs are
coherent is that the information in successive sentences follows some
pattern of inference or of knowledge with which the hearer is familiar,
so that the hearer is able to relate each part to the whole. To signal
such inferences, people usually link successive blocks of text in one
of a fixed set of ways. The inferential nature of such linkage was
noted by Hobbs in 1978. In 1982, McKeown built schemas (scripts) for
constructing some paragraphs with stereotypical structure. Around
the same time, after a wide-ranging linguistic study, Mann proposed
a relatively small number of intersentential relations that suffice to
bind together coherently most of the things people tend to speak about.
The talk will describe a prototype text structurer that is based on the
inferential ideas of Hobbs, uses Mann's relations, and is more general
than the schema applier built by McKeown. The structurer takes the form
of a standard hierarchical expansion planner, in which the relations
act as plans and their constraints on relation fillers (represented
in a formalism similar to Cohen and Levesque's work) as subgoals in the
expansion. The structurer is conceived as part of a general text planner,
but currently functions on its own. It is being tested in two domains:
database output and expert system explanantion.