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The standard, inter-keyword and inter-document associations typically
evaluated as part of keyword and document clustering are part of the
broader context of the associative representation used by AIR. The
system extends these pairwise clustering relations and the fundamental
keyword-document Index relation to include higher-order {\em
transitive} relations as well. That is, if node A is associated with
node B and node B is associated with node C, then node A is also
considered to be associated with node C, but to a lesser extent.
Obviously,
this transitive assumption is not always valid, and this may be why most
IR research has not considered this extension. But AIR was is an
adaptive system, and one of the critical problems facing any learning
system is the generation of {plausible hypotheses}; i.e., theories which
stand a better than average chance of being correct. Transitivity is
considered a default assumption, the consequences of which will be
subjected to adaptation which favor appropriate transitivities and cull
out inappropriate ones.
It is interesting to contrast the adaptive
changes made by AIR in response to RelFbk with the documet
modification strategies of Salton with Brauen et al. [REF566] [REF567] mentioned in Section §4.2.2 (and returned to again in Section
§7.3 ). The query-document matches used
as the basis of their changes considers only direct, keyword-to-document
associations while AIR makes use of a much wider web of indirect
associations as well. To a first approximation the changes made by AIR
to direct keyword-to-document associations are not unlike those proposed
by Salton and Brauen (if I'd only known!). But AIR makes other changes,
to more indirect associations as well.
Salton and Buckley have analyzed
the spreading activation search used in some of these systems and
concluded that it is inferior to more traditional retrieval methods [REF668] [Salton88b] . They point out: ... the
relationships between terms or documents are specified by {\em labeled}
links between the nodes .... the effectiveness of the procedure is
crucially dependent on the {\em availability} of a representative node
association map (p. 4,5) [Emphasis added]
In a weighted, associative
representation the semantics of indexing,inter-document and
inter-keyword clustering links are dropped in favor of a single,
homogeneous ASSOCIATIVE RELATION. AIR treats all three types of
weighted links equally. For example, if inter-document citation data had
been available this information could naturally be included a swell;
again the semantics of these relations would have been dropped in favor
of a simple associative weight. The contrast between the use of use of
spreading activation search in {\em connectionist} networks with its use
in {\em semantic} networks is admittedly a subtle one, but it is also
critically important [REF672] . One
clear difference is that semantic networks typically make logical,
deterministic use of labeled links, while connectionist networks like
AIR rely on weighted links for probabilisitic computations.
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Generalized representation