15. The method according to claim 2 , further comprising: in the aggregating step, aggregating annotations by category contexts such that an annotation corresponds to a category context if it contains the keywords of the category context; determining category contexts that have a predefined minimum number of unique user identifiers and a predefined minimum number of unique item identifiers in their aggregated annotations; and clustering items and users simultaneously by category context such that the unique user identifiers for a determined category context is identified as a cluster of users and the unique item identifiers for the same determined category context is identified as a cluster of items.
15. The method according to claim 2 , further comprising: in the aggregating step, aggregating annotations by category contexts such that an annotation corresponds to a category context if it contains the keywords of the category context; determining category contexts that have a predefined minimum number of unique user identifiers and a predefined minimum number of unique item identifiers in their aggregated annotations; and clustering items and users simultaneously by category context such that the unique user identifiers for a determined category context is identified as a cluster of users and the unique item identifiers for the same determined category context is identified as a cluster of items. 23. The method according to claim 15 , further comprising: offering drilldowns to a search based on the determined category contexts.