8. Apparatus for processing a plurality of linguistic expressions, each linguistic expression originating from an originator, and each linguistic expression being a linguistic expression in which the originator of that linguistic expression expresses a respective sentiment with respect to one or more topics, the apparatus comprising one or more processors configured to: for each linguistic expression, detect one or more topics of interest addressed in that linguistic expression by the originator of that linguistic expression; for each linguistic expression, for each topic detected in that linguistic expression, assess a sentiment of the originator of that linguistic expression with respect to that topic; group the originators into one or more groups based on similarities between the originators' respective sets of detected topic-sentiment pairs; associate, with a given group, semantic information, wherein the semantic information associated with the given group relates to one or more feature selected from a group of features consisting of: properties of one or more members of that given group and the sets of topic-sentiment pairs of one or more of the members of that given group; and for a given originator, create or update a profile; wherein the given originator is a member of the given group; wherein the profile is created or updated such that it comprises attributes of the given originator; and wherein the attributes are dependent upon the given originator's membership in the given group and the semantic information associated with the given group.
11. Apparatus according to claim 8 wherein associating the semantic information with the given group comprises using knowledge of a given topic and knowledge of a predominant sentiment with respect to that given topic of the members of the given group.