code: function addUrlForSchema(oMetaModel, sSchema, sReferenceUri, sDocumentUri) {
  		var sUrl0,
  			mUrls = oMetaModel.mSchema2MetadataUrl[sSchema];
  
  		if (!mUrls) {
  			mUrls = oMetaModel.mSchema2MetadataUrl[sSchema] = {};
  			mUrls[sReferenceUri] = false;
  		} else if (!(sReferenceUri in mUrls)) {
  			sUrl0 = Object.keys(mUrls)[0];
  			if (mUrls[sUrl0]) {
  				// document already processed, no different URLs allowed
  				reportAndThrowError(oMetaModel, "A schema cannot span more than one document: "
  					+ sSchema + " - expected reference URI " + sUrl0 + " but instead saw "
  					+ sReferenceUri, sDocumentUri);
  			}
  			mUrls[sReferenceUri] = false;
  		}
  	}
docs: Adds the given reference URI to the map of reference URIs for schemas.
  
  @param {sap.ui.model.odata.v4.ODataMetaModel} oMetaModel
  The OData metadata model
  @param {string} sSchema
  A namespace of a schema, for example "foo.bar."
  @param {string} sReferenceUri
  A URI to the metadata document for the given schema
  @param {string} [sDocumentUri]
  The URI to the metadata document containing the given reference to the given schema
  @throws {Error}
  If the schema has already been loaded from a different URI