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Time and Relational Theory, 2nd Edition by Nikos Lorentzos, Hugh Darwen, C.J. Date

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Chapter 11

Generalizing the Algebraic Operators

The PACK and UNPACK operators provide the basis for greatly simplifying the formulation of certain kinds of queries that arise frequently in the temporal context, but there’s still room for further improvement. With such considerations in mind, this chapter shows how the familiar operators of the relational algebra can all be generalized appropriately, as U_ operators. To be specific, it discusses U_ versions of the familiar dyadic operators (UNION, INTERSECT, MINUS, D_UNION, I_MINUS, JOIN, MATCHING, NOT MATCHING); the n-adic operators (UNION, INTERSECT, D_UNION, JOIN); and the monadic operators (restrict, project, EXTEND, GROUP, UNGROUP). It also discusses U_ comparison operators. It concludes with ...

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