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again. Searching for the antecedent leads to identifying “a block” and building
an anaphoric relation between “it” and “a block”.
In an MMD system, this process requires various stages. First, we need to
identify the genuinely anaphoric expressions and distinguish them from those
that are references like the ones we have seen so far in this chapter. To this
end, the linguistic form is essential, third person pronouns clearly favor an
anaphoric interpretation, whereas “the block” and “the green one” can refer to
somethingeitherdirectlyoranaphorically: “takearedblockandagreenblock,
put the red one in a box and the green one on top of it”. The impossibility
to solve the direct reference is also a hint: if various referents are possible,
it might be an anaphora. A second stage consists of looking at the gender,
number and potentially category if the anaphoric expression has a head noun,
so as to draw up a list of potential antecedents. When various antecedents have
been identified, a choice then has to be made. The criteria on which this choice
relies are proximity, for example in terms of the number of words between
the antecedent and the anaphora, and salience of the referent matching the
antecedent or grammatical functions: if the antecedent function is the same as
that of the anaphora, there is a syntactic parallel and it is an argument in favor
of that antecedent rather than another antecedent. In NLP as well as in MMD,
this process can be implemented through statistics, or even machine learning,
so as to weigh the importance of each resolution setting versus the tests on the
corpus. In MMD, the antecedent can belong to a previous utterance, and the
speaker's identity is not a limit: the user can anaphorically take up a reference
made by the system, and vice versa.
Until now, our anaphora examples are also coreferences, i.e. the
antecedent and the anaphoric expression refer to the same referent: once the
relation between them is identified, the allocation of a referent to an anaphoric
expression consists of taking up the referent already allocated to the
antecedent. Yet, the anaphora is particular since it can be associative, i.e. use a
conceptual link between two different referents. Thus, “give me a ticket for
Paris. The cost must be less than twenty euros” or “draw a triangle. Color one
side red” involve two referents linked between themselves every time, the
reference to the second understood through the use of the first, by an
associative anaphora relation. The anaphora is not linked to coreference in
that case: the two referents are not the same, and each of them requires its
own reference resolution process.
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