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Generalized representation

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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