MECHANISM FOR STORING DIFFERENT VERSIONS OF INFORMATION ITEMS

摘要

Versions of information items are stored as views. Each view has a common portion and one or more unique portions. For each information item there is a first-order information tuple (200) and one or more n order information tuples (210, 215 ). A metadata (201) field describes the information tuple. A reference count field (202) counts references to the first-order information tuple. A content field (203) indicates the common portion. Each n order information tuple comprises a metadata field (211, 216 ) for the unique portions, a reference count field (212, 217 ) and a reference field (213, 218 ) to a higher-order information tuple. A reference-tracking system increments or decrements the reference field of an information tuple when references to the information tuple are created or deleted. An information tuple is normally deleted when its reference field becomes zero, but is kept for some time if there are external links (251) to it.