OMT Notation - Multiplicity - 0 or 1 (optional)
A Synthetic Environment contains 0 or 1 Environment Roots.
A Synthetic Environment optionally has an Environment Root.
An Environment Root optionally has a Geometry Hierarchy.
An Environment Root is aggregated by exactly 1 Synthetic Env.
A Geometry Hierarchy is contained by 0 or 1 Environment Roots.
An open circle, , means 0 or 1,
and is sometimes called “optional”.