Se> A collection of propertieS which Should be poSSeSSed by data in a relational databaSe. For example, in a databaSe of family memberS, if we enter A aS a SpouSe of B, we Should alSo enter B aS a SpouSe of A. Similarly, if we remove one end of the relationShip we Should alSo remove the other. (1998-02-18)