 Sequences of symbols code more information than multisets and multisets are more expressive than sets. Thus the emergence of writing itself can be seen as a quest to find the most expressive representation of administrative data. When measuring information in sequences of messages it is important to distinguish the aspects of repetition, order and grouping. The extensive aspects of information can be studied in terms of such structural operations (see entry on  substructural logics).  We can study sets of messages in terms of operators defined on sequences of symbols. 