Adding a relation, and its rules
Link two selected records; the link is checked against its relation definition.
Relations and their rules
Add relation links two selected records. The link is checked against its relation definition before it is saved, and refused with the rule named when it breaks one: the record's entity must be the one the definition links (or, when the definition says so, an entity that inherits from it or one of the entities selected for it); neither record may go past its maximum number of links of that kind; the same two records cannot be linked twice when the definition allows one link per pair; and periods cannot overlap when the definition forbids it.