5. The method of claim 4 , wherein the online social system is selected from the group consisting of: blogging; people tagging; social bookmarking; and mini blogging.
4. The method of claim 3 , wherein computing candidate tags further comprises: retrieving information about the user to whom the additional tags are recommended, from at least one online social system; extracting a set of keywords from the retrieved information; and associating an importance score with each keyword, wherein each keyword is a candidate tag.