I think that the authors could have addressed this aspect by stressing the fact that the tasks to be accomplished by a generation system are of much greater variety than those needed for natural language understanding: • On the one hand, many aspects of pragmatics, which is one of the least understood areas in linguistics, are more important in generation than in analysis and, therefore, they have to be captured to a certain extent.
• the initial representations for a generation system are much more distant from the language surface than the results of understanding systems, and they can appear in various, mostly nonlinguistic forms.