A database can contain multiple DBDrawings: floor planes, cell planes, 3D items, shells, etc.
A DBDrawing is similar to a drawing layout; each DBDrawing keeps a set of DBView
items for the drawing.
A DBDrawing and DBView do not own elements and do not have a list of visible
elements. Each DBView selects elements from ElemTable using rules in DBView,
elements, and managers.
Since a created object becomes a database resident object,
its lifecycle is managed by the database.