Designing an Anaphora Resolution Algorithm for Route Instructions

To start with, the anaphoric expressions occurring in the IBL-corpus needed to
be identified and classified. Since there are many anaphoric references occurring in
the IBL-corpus, I had to determine what kind of anaphoric references the algorithm
should handle in the framework of this project. Thus, I will shortly elucidate the types
of anaphoric reference the algorithms deal with. The RIAR-algorithm is designed to
resolve the personal and demonstrative pronouns it, this and that which either refer to
individual entities (e.g. the road) or abstract entities (e.g. turn left). Furthermore, it
deals with so-called ‘This-NP’-anaphors (cf. Poesio & Modjeska 2002) which tend to
refer to individual entities or to implicit entities introduced by previously mentioned
entities. Even though Poesio & Modjeska (2002) only describe cases in which
elements or subsets of plural objects implicitly introduce a plural object into the
discourse model, the IBL-dataset implies that the reverse also applies, which means
that plural objects also implicitly establish their elements or subsets in the discourse
model. The other algorithm, the SR-algorithm, resolves references to spatial locations
expressed in anaphors like here and there. The referents of those anaphors are built
up by the combination of the verb and the spatial preposition of the previous
utterance. Since there are plenty of possible combinations it is quite difficult to define
rules for resolving ‘here/there’-anaphors.
To develop the algorithms a gold standard of resolved anaphoric expressions
was created. For the conceptual design and for the processing of the algorithms it was
useful that the IBL-system is already in charge of an implemented DRT (discourse
representation theory) component, so that the algorithms can make use of the existing
lexicon and ontology. The third part of this dissertation gives details about the
conceptual design and the processing of both algorithms.
Then, the algorithms are tested on the second set of the IBL-corpus (the
unseen data). The fourth part of this work contains an evaluation of the algorithms
and a discussion of the most common problems observed during the testing phase.
Finally, the conclusion section considers unsolved problems, and suggestions
for further work are made.
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