NOTIONS OF UPWARD COMPATIBILITY OF TEMPOR AL QUERY LANGUAGES

Migrating applications from conventional to temporal database manageme nt technology has received scant mention in the research literature. T his paper formally defines three increasingly restrictive notions of u pward compatibility which capture properties of a temporal SQL with re spect to conventional SQL that, when satisfied, provide for a smooth m igration of legacy applications to a temporal system. The notions of u pward compatibility dictate the semantics of conventional SQL statemen ts and constrain the semantics of extensions to these statements. The paper evaluates the seven extant temporal extensions to SQL, all of wh ich are shown to complicate migration through design decisions that vi olate one or more of these notions. We then outline how SQL-92 can be systematically extended to become a temporal query language that satis fies all three notions.