Most of the generation systems use grammars that are specifically designed for generation purposes (cf. [Dale1990], [Horacek1990], [McKeown et al.1990], [Neumann and Finkler1990]). The purpose of this paper is to show that the use of a reversible architecture for grammatical processing has important influences on the generation task. A thorough-going use of a reversible grammar within a natural language generation system affects the separation into strategic and tactical components. On the one hand, problems with this separation emerge; on the other hand reversible architectures will serve as an important (linguistic) basis to achieve first solutions to the problems.
In section 3 we discuss in more depth important problems and restrictions with the modular design of current natural language generation systems. The problem can be summarized as follows. Since a tactical component is mainly guided by the compositional structure of the semantic input, it cannot control by itself those particular combinations of partial strings of the whole utterance which will lead to alternative derivations when the hearer is parsing this utterance. This means that possible ambiguities are out of the generator's view, and will only arise during parsing.
In order to overcome these problems we propose an integrated approach of parsing and generation based on reversible grammars in section 4. A major point of this approach is that one mode of operation (e.g., parsing) is used for monitoring the other mode (e.g, generation).
In sections 5 a mechanism is presented which ensures that the generator, if so desired, only generates a non-ambiguous utterance for a given semantic specification. This mechanism uses a monitor which is based on the parsing component. The monitor gives feedback to the generation system in the form of annotated derivation trees which locate the current ambiguities. The generator uses such decorated derivation trees to avoid those ambiguities. Clearly this use of derivation trees only makes sense if the derivation trees have the same meaning for both components, i.e. they refer to the same reversible grammar.
In section 6 we describe the use of the integrated approach for a mechanims which generates paraphrases in an interactive disambiguation component. Again the parsing and generation component communicate through the use of derivation trees. Therefore the proposed mechanism is strongly dependent on the use of a single reversible grammar.