leg element describes one
of the legs of a relationship type.
A leg is given by its codomain (an entity type) and information on the cardinality and editing constraints.
The identifier of the entity type this leg points to.
A label for this leg. The user will be always presented with this label when dealing with the relationship type this leg appears in from the pointed entity type.
A detailed help text for this leg (for tooltips).
The lower bound for this leg. It may be 0 (the default) or 1.
The upper bound for this leg. It may be 1, N or M (the default).
This field can be set to true or false (the default). In the first case, the entity type referenced by this leg becomes weak, and the entity type referenced by the other leg becomes one of its owners. The cardinality constraint on this leg must be (1:1), and the one on the other leg (x:N).
This field can be set to true (the default) or false. In the first case, the relationship type containing this leg will be editable from the entities of the pointed type.
Technically we defined legs on multirelations, which are the semantics of relationship types, but the reader will forgive us if we extend the term.