KERML — Performances can be objects, behaviors can be structures

Clause 9.2.5.1 (Objects Overview) says

Objects and Performances do not overlap

but Objects::Object and Performances::Performance are not disjoint in the libraries.

Clause 7.4.4 (Structures) says

Structures and behaviors do not overlap,

but there is no constraint for this.

Make Object and Performance disjoint

Objects::Object and Performances::Performance can be made disjoint. There is currently no metaclass in the abstract syntax that is both a Structure and a Behavior. However, there is currently nothing to prevent a Structure from specializing a Behavior, or vice versa, which would violate the disjointness of Object and Performance. There needs to be a constraint to prevent this (similar to the validateClassSpecialization constraint that prevents Classes from specializing DataTypes or Associations).