1. A method comprising: storing in a database a first annotation and a second annotation, the first annotation relating to a first content unit and comprising a first semantic label and first content, the first semantic label indicating a semantic classification of the first content, the second annotation relating to a second content unit and comprising a second semantic label and second content, the second semantic label indicating a semantic classification of the second content, the semantic classification of the second content being different from the semantic classification of the first content, wherein the storing comprises storing the first semantic label for the first annotation and the second semantic label for the second annotation in a first table of the database, and storing the first content of the first annotation and the second content of the second annotation in at least one second table of the database different from the first table.