1 : A method for adding a new record to a hierarchical set of records having a plurality of hierarchical levels and a plurality of hierarchical depths, each of the records in the hierarchical set of records having a tag that is unique within the hierarchical set of records, the method comprising: identifying one of the records in the hierarchical set of records as the parent of the new record; modifying the tag, thereby producing a key; adding the key to the new record; indexing the hierarchical set of records, thereby adding the new record to the hierarchical set of records, wherein indexing the hierarchical set of records comprises applying the key to the hierarchical set of records; and retrieving the added record with the key which comprises a second tag uniquely identifying the added record, and wherein each tag comprises a number including multiple digits indicating a depth and a level within the hierarchical set of records, and wherein the modifying comprises selecting a digit and changing a value of the digit, thereby changing the level or the depth, or both, of said one of the records, and wherein the applying comprises selecting one or more records in the hierarchical set of the records having a tag that matches the key.