However, the dialogue manager will decide in both cases that this is a correction of the destination town.
Since semantic analysis is the input for the dialogue manager, we have therefore measured concept accuracy in terms of a simplified version of the update language. Following a somewhat similar proposal in Boros et al. (1996), we translate each update into a set of ``semantic units'', were a unit in our case is a triple . For instance, the examples above translate as
Both the updates in the annotated corpus and the updates produced by the system are translated into semantic units of the form given above. The syntax of the semantic unit language and the translation of updates to semantic units is defined in van Noord (1997), but note that the translation of updates to semantic units is relatively straightforward and is not expected to be a source of discussion, because the relation is many to one.
Semantic accuracy can now be defined as follows. Firstly, we list the proportion of utterances for which the corresponding semantic units exactly match the semantic units of the annotation ( exact match). Furthermore we calculate precision (the number of correct semantic units divided by the number of semantic units which were produced) and recall (the number of correct semantic units divided by the number of semantic units of the annotation). Finally, following Boros et al. (1996) we also present concept accuracy as
where SU is the total number of semantic units in the corpus annotation, and SUS, SUI, and SUD are the number of substitutions, insertions, and deletions that are necessary to make the (translated) update of the analysis equivalent to (the translation of) the corpus update.