SYNTAX:
constant_ref   = [schema_instance_id ?::?] constant_id .
entity_ref   = [schema_instance_id ?::?] entity_id .
enumeration_ref  = [schema_instance_id ?::?] enumeration_id .
type_ref    = [schema_instance_id ?::?] type_id .
Extended References are introduced, to be able to uniquely reference identifiers in the global scope of the mapping schema. The global scope of the Source Schema, plus the global scope of the Target Schema, plus the outer scope of the mapping schema, constitutes the global scope of an EDMexpressX^ mapping schema.
Constants, entities, defined types, and enumeration elements are the identifier types in the source and target schemata that can be directly referenced from a mapping schema. A notation is required to uniquely reference these identifier types within an EDMexpressX^ construct, in case the same name is used for more than one identifier in the mapping schema global scope.
This notation is called an Extended Reference. An Extended Reference consist of an optional schema instance identifier followed by a double colon, followed by the identifier name.
Example:
cartesian_point
source::person
ap214::address