D. Goldberg, D. Nichols, B. Oki, and D. Terry. Using collaborative filtering to weave an information tapestry. Communications of the ACM, 35(12):61–70, December 1992.
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This paper illustrates a simple intelligent mechanism by which people collaborate to help one another perform filtering by recording they reactions to the document they read. These reactions, called annotations, can be accessed by other’s filters.