The Relations.1 (or Relations.n) relation set is added to the
tree right below the Relations node.
Note:
Formulas, design tables, rules, checks, reactions and
knowledge patterns can be created in relation sets. When no relation set has
been created, the destination box of the relation editor is by default
initialized to the Relations node (except for knowledge patterns where there
is no destination field and for which you must first select the destination
relations set.