Surrogates are by definition time invariant. The opposite of time invariant is time varying. In the schema R above, the courses taken by a student varies over time, and the attribute Course is time varying. G. M. Nijssen. A description of the time domains is given shortly.
Surrogates are system generated unique internal identifiers.
Relations and Entities . We also assume that a domain of surrogates is included among these domains. Surrogate values are used for representing real world objects. Relations and Entities . In G. M. Nijssen, editor, Modelling in Data Base Management Systems, pp.