diff --git a/basyx/aas/model/base.py b/basyx/aas/model/base.py
index 9d582a091..80060d68c 100644
--- a/basyx/aas/model/base.py
+++ b/basyx/aas/model/base.py
@@ -1767,10 +1767,10 @@ def remove_object_by_semantic_id(self, semantic_id: Reference) -> None:
 
 # TODO: Find a better solution for providing constraint ids
 ATTRIBUTES_CONSTRAINT_IDS = {
-    "id_short": 117, # Referable,
+    "id_short": 22, # Referable,
     "type": 21, # Qualifier,
     "name": 77, # Extension,
-    "semantic_id": 134, # model.OperationVariable
+    # "id_short": 134, # model.OperationVariable
 }
 
 
@@ -1891,7 +1891,7 @@ def _validate_namespace_constraints(self, element: _NSO):
                 if hasattr(element, key_attr_name):
                     key_attr_value = self._get_attribute(element, key_attr_name, case_sensitive)
                     self._check_attr_is_not_none(element, key_attr_name, key_attr_value)
-                    self._check_value_is_not_in_backend(key_attr_name, key_attr_value, backend_dict, set_)
+                    self._check_value_is_not_in_backend(element, key_attr_name, key_attr_value, backend_dict, set_)
 
     def _check_attr_is_not_none(self, element: _NSO, attr_name: str, attr):
         if attr is None:
@@ -1901,13 +1901,14 @@ def _check_attr_is_not_none(self, element: _NSO, attr_name: str, attr):
             else:
                 raise ValueError(f"{element!r} has attribute {attr_name}=None, which is not allowed!")
 
-    def _check_value_is_not_in_backend(self, attr_name: str, attr, backend_dict: Dict, set_: "NamespaceSet"):
+    def _check_value_is_not_in_backend(self, element: _NSO, attr_name: str, attr,
+                                       backend_dict: Dict[ATTRIBUTE_TYPES, _NSO], set_: "NamespaceSet"):
         if attr in backend_dict:
             if set_ is self:
-                text = f"Object with attribute (name='{attr_name}', value='{attr}') " \
+                text = f"Object with attribute (name='{attr_name}', value='{getattr(element, attr_name)}') " \
                        f"is already present in this set of objects"
             else:
-                text = f"Object with attribute (name='{attr_name}', value='{attr}') " \
+                text = f"Object with attribute (name='{attr_name}', value='{getattr(element, attr_name)}') " \
                        f"is already present in another set in the same namespace"
             raise AASConstraintViolation(ATTRIBUTES_CONSTRAINT_IDS.get(attr_name, 0), text)
 
diff --git a/test/model/test_base.py b/test/model/test_base.py
index ef894de50..13db21f95 100644
--- a/test/model/test_base.py
+++ b/test/model/test_base.py
@@ -374,7 +374,7 @@ def test_NamespaceSet(self) -> None:
         self.assertEqual(
             "Object with attribute (name='semantic_id', value='ExternalReference(key=(Key("
             "type=GLOBAL_REFERENCE, value=http://acplt.org/Test1),))') is already present in this set of objects "
-            "(Constraint AASd-022)",
+            "(Constraint AASd-000)",
             str(cm.exception))
         self.namespace.set2.add(self.prop5)
         self.namespace.set2.add(self.prop6)
@@ -389,7 +389,7 @@ def test_NamespaceSet(self) -> None:
         self.assertEqual(
             "Object with attribute (name='semantic_id', value='"
             "ExternalReference(key=(Key(type=GLOBAL_REFERENCE, value=http://acplt.org/Test1),))')"
-            " is already present in another set in the same namespace (Constraint AASd-022)",
+            " is already present in another set in the same namespace (Constraint AASd-000)",
             str(cm.exception))
 
         self.assertIs(self.prop1, self.namespace.set1.get("id_short", "Prop1"))
@@ -456,7 +456,7 @@ def test_NamespaceSet(self) -> None:
         with self.assertRaises(model.AASConstraintViolation) as cm:
             self.namespace3.set1.add(self.qualifier1alt)
         self.assertEqual("Object with attribute (name='type', value='type1') is already present in this set "
-                         "of objects (Constraint AASd-022)",
+                         "of objects (Constraint AASd-021)",
                          str(cm.exception))
 
     def test_namespaceset_hooks(self) -> None: