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We introduce a nested bitemporal relational data model that allows arbitrary levels of nesting. Bitemporal data is attached to attributes. The fundamental construct for representing temporal data is a bitemporal atom that consists of three parts: transaction time, valid time and a value. We have defined algebra for the nested bitemporal relational model. The algebra includes operations to manipulate bitemporal data, to restructure nested bitemporal relations and to rollback database to a designated state in the past. We have also defined the concept of ‘context' for using temporal data. Bitemporal context is for auditing purposes and rollback context is for querying past states of a bitemporal database. [ABSTRACT FROM AUTHOR]