Chapter 3 – Time and the Database

Publisher Summary This chapter discusses time and the database. A temporal database is a database that contains historical data instead of or in addition to current data. Such databases have been under active investigation since the early 1980s. Some of those investigations have taken the extreme position that data in such a database, once inserted, should never be deleted or changed in any way, in which case the database can be thought of as containing historical data only. Conventional databases, by contrast, are typically at the other extreme; such a database typically contains current data only, and data in such a database is changed or deleted as soon as the propositions represented by that data cease to be ones that evaluate to true. The propositions in nontemporal database are generally taken to be true “now,” that is, at the time the database is inspected. Temporal database research has therefore involved a certain amount of investigation into the nature of time itself. This chapter explores some questions that regarding whether or not time has a beginning or an end; if time is a continuum or is it divided into discrete quanta; and the best way to characterize the important concept “now.”