A foundation for vacuuming temporal databases

A wide range of real-world database applications, including financial and medical applications, are faced with accountability and traceability requirements. These requirements lead to the replacement of the usual update-in-place policy by an append-only policy, resulting in so-called transaction-time databases. These databases retain all previous states and are therefore ever-growing. A variety of physical storage structures and indexing techniques as well as query languages have been proposed for transaction-time databases, but the support for physical deletion, termed vacuuming, has only received little attention. Such vacuuming is called for by, e.g., the laws of many countries and the policies of many businesses. Although necessary, with vacuuming, the database’s perfect and reliable recollection of the past may be manipulated via, e.g., selective removal of records pertaining to past states. This paper provides a semantic foundation for the vacuuming of transaction-time databases. The main focus is to establish a foundation for the correct processing of queries and updates against vacuumed databases. However, options for user, application, and database interactions in response to queries and updates against vacuumed data are also outlined.