Unni Cathrine Eiken February 2005

4.4 Are concept classes useful for anaphora resolution?
The EPAS list has been processed in different ways in this chapter. The tests which have been
described provide an indication of how context patterns extracted from the text collection can be
used to create expectations of which words (or which type of words) that are likely to occur in a
given contextual environment. These expectations can be used to anticipate which word, or
rather which concept, might be the antecedent for an anaphor. The concept groups which
emerged in the association process are simply classes of semantically related words which tend
to have similar contextual distributions within the domain of the text corpus. In order to indicate
the usefulness of such concept classes in the process of resolving an anaphor, the test set of the
EPAS list (all EPAS containing pronouns) was processed with different methods. In (4-13) the
results of these methods are shown. In addition to the tests in TiMBL described in the above, the
anaphors in the test set were resolved manually using the Lappin and Leass approach as
described in section 2.1.2. For these test, the sentence with the anaphor, as well as the preceding
sentence, was considered in each case. This purely syntactic approach identified the correct
antecedent in 16 of the 32 test instances.
(4- 13)
Method Correct assignments
Syntactic method 50% (16/32)
TiMBL 46.87% (15/32)
TiMBL with concept groups 78,12% (25/32)
The results shown in (4-13) suggest that using concept groups may indeed be a useful approach
in anaphora resolution. Especially in the case of anaphoric expressions where the antecedent is
not clearly stated in the text it may be useful to have an idea of which type of antecedent one
might expect. 10 of the 32 EPAS containing pronouns were of this kind. The syntactic approach
could naturally not resolve these anaphors, as an antecedent not clearly present in the text hardly
can feature on a list of possible candidates. These types of anaphors require real-world or
domain knowledge to be resolved. In the case of 4 of these 10 EPAS, the EPAS list could not be
consulted to find likely antecedents. Because of the small size of the data set, some predicates
only feature once. This was the case for the five predicates jobbe-utfra (work-from), kartlegge
(map), ta (take), varsle (notify) and ville (want) which all only co-occur with pronouns. With the
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