Designing an Anaphora Resolution Algorithm for Route Instructions

However, as in Eckert & Strube’s algorithm, the discourse position also
controls the status of the entities in the S-List. Entities mentioned in the same unit as
the anaphor are more highly ranked than entities mentioned in the previous unit.
Within one unit the first mentioned entity is more salient than entities mentioned later
in the unit. The entity which is in the first position of the S-List is the preferred
antecedent of the anaphor. So if the corresponding rule is applied, the anaphor will be
resolved to the first entity in the S-List.
Unlike in Eckert & Strube’s account, the S-List is not updated and cleaned (which
means that all discourse entities from the previous unit which are not realised again in
actual unit are removed from the S-List). Eckert & Strube have no discourse model
or, in other words, they only model the attentional state of the hearer as the S-List
which is a partial discourse model including only highly salient entities. The RIARalgorithm
only constructs a S-List when it hits an unresolved anaphor. The content of
the S-List is always deleted after the anaphor is resolved and a completely new S-List
is built up for the next unresolved anaphor.
The concept of an implicit S-List derives from the observation that some
entities are plural objects or complex entities which consists of several elements of
subsets (e.g. crossroads which consists of two crossing roads). The ‘normal’ S-List
only contains entities which are conceptually related to the anaphor (hyper- or
subtype of the anaphor or the same type as the anaphor). The implicit S-List is built
up if a ‘This-NP’-anaphor occurs and if the concept of its NP is either an
element_entity or a complex_entity. If the NP-concept is a element_entity (e.g. ‘this
road’), the implicit S-List contains all entities which have the same concept as the
corresponding complex_entity of the element_entity (e.g. ‘crossing’, ‘junction’,
‘crossroads’ etc.). Conversely, if the NP-concept is a complex_entity (e.g. ‘this
junction’) all entities of the same type as corresponding element_entities are put into
the S-List (e.g. ‘road’, ‘street’, ‘branch’ etc.). Like the S-List, the implicit S-List only
contains entities mentioned in the previous unit or in the same unit as the anaphor.
The RIAR-algorithm resolves discourse deictic anaphors almost in the same
way as the Eckert & Strube-algorithm. As soon as the anaphor is marked as I-
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