set relation

Set relations describe mainly subset/superset relations between collections. In contrast to set methods set relations describe a state or an extensional feature.

Set relations are based on instance identities (LOID), i.e. elements in a set are considered as being identified by its LOIDs. Set relations for controlled extents are maintained automatically, which leads to some specific rules for creating and deleting instances in intersect or union extents.

Set relations are defined as collection feature (extensional feature), i.e. in contrast to set methods, set relations are stored and become subject of database consistency. Between local collections only subset/superset relations can be defined. Between controlled extents subset/superset relations, intersect, distinct and union relations can be defined.