Designing an Anaphora Resolution Algorithm for Route Instructions
Designing an Anaphora Resolution Algorithm for Route Instructions
Designing an Anaphora Resolution Algorithm for Route Instructions
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But Sidner suggests that the chosen referent <strong>for</strong> a pronoun is always the focused<br />
entity in the discourse model except if the sem<strong>an</strong>tic properties of the referent <strong>an</strong>d the<br />
predication context of the pronoun are incompatible. The focused entity in this<br />
example is the noun phrase referring to ‘the dog’ since it is the object of the previous<br />
sentence, there<strong>for</strong>e ‘the dog’ is the preferred referent of the pronoun rather th<strong>an</strong> ‘the<br />
bull’.<br />
But as mentioned above, there are different techniques to determine the<br />
‘focus’. The Centering Theory defines several relations between two adjacent<br />
utter<strong>an</strong>ces. It assumes that each utter<strong>an</strong>ce introduces new entities into the discourse.<br />
These entities are the so-called Forward Looking Centers (CF). They are r<strong>an</strong>ked with<br />
respect to different criteria (e.g. grammatical role, in<strong>for</strong>mation structure, coherence<br />
structure etc.). The most highly r<strong>an</strong>ked entity in the CF of the previous utter<strong>an</strong>ce(U i-1 )<br />
is the focused entity in <strong>an</strong> utter<strong>an</strong>ce(U i ) (the so-called Backward-Looking Center<br />
(CB)). It needs to be said that the Centering Theory does not specify what<br />
‘utter<strong>an</strong>ces’ are, how the entities in the CF are r<strong>an</strong>ked, what kind of entities are<br />
introduced into the discourse <strong>an</strong>d how they are created. Thus, researchers using the<br />
theory have to define those principles on their own.<br />
Applying salience to resolve pronouns which refer to noun phrases works<br />
quite well but it helps to find the correct referent of deictic pronouns. Due to the fact<br />
that deictic pronouns tend to have clausal <strong>an</strong>tecedent <strong>an</strong>d according to the observation<br />
that they refer to sem<strong>an</strong>tically complex non-focused items, the Centering Theory does<br />
not succeed in resolving deictic pronouns. Nevertheless, Grosz & Sidner (1986)<br />
discuss the concept of a global focus which they characterize as the set of entities<br />
being part of the attentional state of the discourse particip<strong>an</strong>ts. So even if there is only<br />
one entity in <strong>an</strong> utter<strong>an</strong>ce ‘in focus’, the other ones are ‘activated’ or in Poesio &<br />
Modjeska’s (2002) words ‘sufficiently salient’. They are in the short-term memory<br />
because they are mentioned in the discourse or because they are in the physical<br />
context (cf. example (3) above). According to Gundel et al’s (1993) Givenness<br />
Hierarchy (quoted from Poesio & Modjeska 2002) personal pronouns usually refer to<br />
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