A more suitable strategy would be to generate only one paraphrase for each ambiguous logical form. As long as parsing and generation are performed in an isolated way the problem with this strategy is that there is no control over the choice of paraphrases. In order to make clear this point I will look closer to the underlying structure of the example's utterances.
The problem why there are two readings is that the PP `with the system folder' can be attached into modifier position of the NP `the folder' (expressing the semantic relation that `folder' contains `system tools') or of the verb 'remove' (expressing semantically that `system tools' is the instrument of the described situation). The example feature structures 13 and 14 (see section 5.2) show the internal grammatical structure in a HPSG-style notation (omitting details that are not relevant in this context).
As long as the source of the ambiguity is not known it is possible to generate in both cases the utterance `Remove the folder with the system-tools' as a paraphrase of itself. Of course, it is possible to compare the resulting strings with the input string S. But because the source of the ambiguity is not known the loop between the isolated processes must be performed several times in general.
A better strategy would be to recognize relevant sources of ambiguities during parsing and to use this information to guide the generation process. Meteer and Shaked MeteerShaked:88 propose an approach where during the repeated parse of an ambiguous utterance potential sources of ambiguity can be detected. For example when in the case of lexical ambiguity a noun can be associated to two semantic classes a so called `lexical ambiguity specialist' records the noun as the ambiguity source and the two different classes. These two classes are then explicitly used in the generator input and are realized, e.g., as modifiers for the ambiguous noun.
The only common knowledge source for the paraphraser is a high order intensional logic language called World Model Language. It serves as the interface between parser and generator. The problem with this approach is that parsing and generation are performed in an isolated way using two different grammars. If an ambiguous utterance S need to be paraphrased S has to be parsed again. During this repeated parse all potential ambiguities have to be recognized and recorded (i.e. have to be monitored) by means of different `ambiguity specialists'. The problem here is that also local ambiguities have to be considered that are not relevant for the whole structure.