Schema Instance declaration

---

The schema instance declaration in the global declaration is mandatory. The defined schema_instance_id is a placeholder for the population of a specific schema. The current version of EDMexpressX^ allows for only two schema instance identifiers to be defined, namely one id that refers to a population of the source schema and another one that refers to a population of target schema..
The scope of the schema instance identifier is the mapping schema in which the schema instance declaration occurs, i.e. the global scope of an EDMexpressX^ mapping schema.