``Degenerate bitemporal relation'' names a previously unnamed concept that is frequently used. A degenerate bitemporal relation resembles a transaction-time relation in that only one timestamp is necessary. Unlike a transaction-time relation, however, it is possible to pose both valid-time and transaction-time queries on a degenerate bitemporal relation.
The use of ``degenerate'' is intended to reflect that the two time dimensions may be represented as one, with the resulting limited capabilities.