diff --git a/src/main/java/org/gcube/resourcemanagement/model/reference/entities/facets/IdentifierFacet.java b/src/main/java/org/gcube/resourcemanagement/model/reference/entities/facets/IdentifierFacet.java
index c747dfb..392e385 100644
--- a/src/main/java/org/gcube/resourcemanagement/model/reference/entities/facets/IdentifierFacet.java
+++ b/src/main/java/org/gcube/resourcemanagement/model/reference/entities/facets/IdentifierFacet.java
@@ -24,7 +24,7 @@ public interface IdentifierFacet extends Facet {
 	public static final String TYPE_PROPERTY = "type";
 	
 	public enum IdentificationType {
-		URI, DOI, IRI, URL, URN, UUID
+		URI, DOI, IRI, URL, URN, UUID, STRING
 	}
 	
 	@ISProperty(name=VALUE_PROPERTY, mandatory=true, nullable=false)