The business layer must use only the defined specializations. Three types are abstract and must not be instantiated in models: the internal active structure element, the internal behaviour element and the passive structure element of the business layer. Any element may have composition, aggregation and specialization links to elements of its own type, and indirect links are derived under Section 5.7.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.