As an editor I want to refer to existing Schemas in statements in order to make it easier to find and classify them. We need a new datatype to link to them from statements.
**Example:**
Q5: corresponding EntitySchema:E1234
**BDD**
GIVEN an Item
AND an Schema covering the same topic
THEN a new statement can be added that links the Item and the Schema
**Acceptance criteria:**
[] a new datatype exists that allows linking to Schemas
[] Only existing Entity Schemas can be selected as values
[] Link text should be the ID of the entity schema
[] The value of that link should be exported in RDF as a URI (schema is to be decided by Engineers)
[] "What Links Here" on an EntitySchema instance should list all entities linking to it through the new datatype
**Notes**:
* In the search field, the schema ID is to be used (e.g. no search by label etc)