diff --git a/src/__init__.py b/src/__init__.py
deleted file mode 100644
index e69de29b..00000000
diff --git a/src/oaklib/cli.py b/src/oaklib/cli.py
index 1f3b0fc5..f92e7dd5 100644
--- a/src/oaklib/cli.py
+++ b/src/oaklib/cli.py
@@ -2354,10 +2354,25 @@ def apply_obsolete(output, output_type, terms):
     show_default=True,
     help="If true, then all sources are in the main input ontology",
 )
+@click.option(
+    "--add-labels/--no-add-labels",
+    default=False,
+    show_default=True,
+    help="Populate empty labels with URI fragments or CURIE local IDs, for ontologies that use semantic IDs",
+)
+@predicates_option
 @output_option
 @output_type_option
 def diff_via_mappings(
-    source, mapping_input, intra, other_input, other_input_type, output_type, output
+    source,
+    mapping_input,
+    intra,
+    add_labels,
+    other_input,
+    other_input_type,
+    predicates,
+    output_type,
+    output,
 ):
     """
     Calculates a relational diff between ontologies in two sources using the combined mappings
@@ -2388,8 +2403,22 @@ def diff_via_mappings(
     else:
         mappings = None
         logging.info("Mappings will be derived from ontologies")
+    if source:
+        sources = list(source)
+        if len(sources) == 1:
+            raise ValueError(
+                f"If --source is specified, must pass more than one. You specified: {sources}"
+            )
+    else:
+        sources = None
+    actual_predicates = _process_predicates_arg(predicates)
     for r in calculate_pairwise_relational_diff(
-        oi, other_oi, sources=list(source), mappings=mappings
+        oi,
+        other_oi,
+        sources=sources,
+        mappings=mappings,
+        add_labels=add_labels,
+        predicates=actual_predicates,
     ):
         writer.emit(r)
 
diff --git a/src/oaklib/utilities/label_utilities.py b/src/oaklib/utilities/label_utilities.py
new file mode 100644
index 00000000..1aae84b8
--- /dev/null
+++ b/src/oaklib/utilities/label_utilities.py
@@ -0,0 +1,27 @@
+from typing import List, Tuple, Union
+
+from linkml_runtime.linkml_model import SlotDefinitionName
+from linkml_runtime.utils.yamlutils import YAMLRoot
+
+from oaklib import BasicOntologyInterface
+
+
+def add_labels_to_object(
+    oi: BasicOntologyInterface,
+    obj: YAMLRoot,
+    pairs: List[Tuple[Union[SlotDefinitionName, str], Union[SlotDefinitionName, str]]],
+) -> None:
+    """
+    Adds labels to an object, for a set of id-label relation pairs
+
+    :param oi: an ontology interface for making label lookups
+    :param obj: object to be filled
+    :param pairs: list of slot name pairs
+    :return: None
+    """
+    for curie_slot, label_slot in pairs:
+        curie = getattr(obj, curie_slot, None)
+        if curie is not None:
+            label = oi.get_label_by_curie(curie)
+            if label is not None:
+                setattr(obj, label_slot, label)
diff --git a/src/oaklib/utilities/mapping/cross_ontology_diffs.py b/src/oaklib/utilities/mapping/cross_ontology_diffs.py
index 1cbc3c5e..dfe93bca 100644
--- a/src/oaklib/utilities/mapping/cross_ontology_diffs.py
+++ b/src/oaklib/utilities/mapping/cross_ontology_diffs.py
@@ -16,6 +16,7 @@ from oaklib.interfaces import MappingProviderInterface, RelationGraphInterface
 from oaklib.interfaces.obograph_interface import OboGraphInterface
 from oaklib.types import CURIE, PRED_CURIE
 from oaklib.utilities.graph.networkx_bridge import mappings_to_graph
+from oaklib.utilities.label_utilities import add_labels_to_object
 
 ONE_TO_ZERO = MappingCardinalityEnum(MappingCardinalityEnum["1:0"])
 ONE_TO_MANY = MappingCardinalityEnum(MappingCardinalityEnum["1:n"])
@@ -77,6 +78,8 @@ def calculate_pairwise_relational_diff(
     right_oi: MappingProviderInterface,
     sources: List[str],
     mappings: Optional[List[Mapping]] = None,
+    predicates: Optional[List[PRED_CURIE]] = None,
+    add_labels=False,
 ) -> Iterator[RelationalDiff]:
     """
     Calculates a relational diff between ontologies in two sources using the combined mappings
@@ -97,12 +100,42 @@ def calculate_pairwise_relational_diff(
     g = mappings_to_graph(mappings)
     if isinstance(left_oi, OboGraphInterface) and isinstance(right_oi, OboGraphInterface):
         for subject_child in left_oi.all_entity_curies():
+            if not curie_has_prefix(subject_child, sources):
+                continue
             for pred, subject_parent in relation_dict_as_tuples(
                 left_oi.get_outgoing_relationship_map_by_curie(subject_child)
             ):
+                if predicates and pred not in predicates:
+                    continue
+                if not curie_has_prefix(subject_parent, sources):
+                    continue
                 for r in calculate_pairwise_relational_diff_for_edge(
-                    left_oi, right_oi, sources, g, subject_child, pred, subject_parent
+                    left_oi,
+                    right_oi,
+                    sources,
+                    g,
+                    subject_child,
+                    pred,
+                    subject_parent,
+                    predicates=predicates,
                 ):
+                    if add_labels:
+                        add_labels_to_object(
+                            left_oi,
+                            r,
+                            [
+                                ("left_subject_id", "left_subject_label"),
+                                ("left_object_id", "left_object_label"),
+                            ],
+                        )
+                        add_labels_to_object(
+                            right_oi,
+                            r,
+                            [
+                                ("right_subject_id", "right_subject_label"),
+                                ("right_object_id", "right_object_label"),
+                            ],
+                        )
                     yield r
     else:
         raise NotImplementedError
@@ -157,6 +190,7 @@ def calculate_pairwise_relational_diff_for_edge(
     candidates: List[RelationalDiff] = []
     for right_subject in right_subject_list:
         right_subject_ancs = list(right_oi.ancestors(right_subject, predicates=predicates))
+        # logging.debug(f"RIGHT: {right_subject} // ANCS[{predicates}] = {right_subject_ancs}")
         right_subject_parents = []
         right_subject_direct_outgoing = defaultdict(list)
         for p, o in right_oi.get_outgoing_relationships(right_subject):

diff --git a/tests/test_utilities/test_cross_ontology_diff.py b/tests/test_utilities/test_cross_ontology_diff.py
index 33a3e800..09ace3de 100644
--- a/tests/test_utilities/test_cross_ontology_diff.py
+++ b/tests/test_utilities/test_cross_ontology_diff.py
@@ -4,6 +4,7 @@ import yaml
 from linkml_runtime.dumpers import yaml_dumper
 
 from oaklib.datamodels.cross_ontology_diff import RelationalDiff
+from oaklib.datamodels.vocabulary import IS_A, PART_OF
 from oaklib.implementations.pronto.pronto_implementation import ProntoImplementation
 from oaklib.implementations.sparql.sparql_implementation import SparqlImplementation
 from oaklib.resource import OntologyResource
@@ -36,3 +37,25 @@ class TestStructuralDiff(unittest.TestCase):
             results = list(calculate_pairwise_relational_diff(oi, oi, ["X", "Y", "Z"]))
             yaml_dumper.dump(results, str(TEST_OUT))
             self.assertCountEqual(expected_results, results)
+
+    def test_structural_diff_with_preds(self):
+        expected_results = yaml.safe_load(open(EXPECTED))
+        expected_results = [RelationalDiff(**obj) for obj in expected_results]
+        for oi in [self.oi, self.owl_oi]:
+            results = list(
+                calculate_pairwise_relational_diff(
+                    oi, oi, ["X", "Y", "Z"], predicates=[IS_A, PART_OF]
+                )
+            )
+            yaml_dumper.dump(results, str(TEST_OUT))
+            self.assertCountEqual(expected_results, results)
+            results = list(
+                calculate_pairwise_relational_diff(oi, oi, ["X", "Y", "Z"], predicates=[PART_OF])
+            )
+            # print(yaml_dumper.dumps(results))
+            self.assertEqual(2, len(results))
+
+    def test_restrict_to_sources(self):
+        for oi in [self.oi, self.owl_oi]:
+            results = list(calculate_pairwise_relational_diff(oi, oi, ["Z"]))
+            self.assertEqual([], results)

--verbose option no longer working
Previously `-v` logged at INFO level, `-vv` at debug, but now this has stopped working
tests/test_utilities/test_cross_ontology_diff.py::TestStructuralDiff::test_restrict_to_sources tests/test_utilities/test_cross_ontology_diff.py::TestStructuralDiff::test_structural_diff_with_preds
tests/test_utilities/test_cross_ontology_diff.py::TestStructuralDiff::test_structural_diff