1. A method for determining which version of a data item to supply to a session, the method comprising the computer-implemented steps of: maintaining a LAST-TO-SEE-TIMESTAMP, associated with the session, which indicates a time of a last change made in the session that must be seen by the session; maintaining with a data item version a CLONE-TIME that indicates a time at which the data item version was current; and determining that the data item version is to be supplied to the session based, at least in part, on a comparison between the CLONE-TIME and the LAST-TO-SEE-TIMESTAMP.