diff --git a/examples/docs_to_kg/main.py b/examples/docs_to_kg/main.py
index 2fa49b36..fb4c23e4 100644
--- a/examples/docs_to_kg/main.py
+++ b/examples/docs_to_kg/main.py
@@ -5,6 +5,11 @@
 from dotenv import load_dotenv
 import cocoindex
 
+@dataclasses.dataclass
+class DocumentSummary:
+    """Describe a summary of a document."""
+    title: str
+    summary: str
 
 @dataclasses.dataclass
 class Relationship:
@@ -31,13 +36,25 @@ def docs_to_kg_flow(flow_builder: cocoindex.FlowBuilder, data_scope: cocoindex.D
         cocoindex.sources.LocalFile(path="../../docs/docs/core",
                                     included_patterns=["*.md", "*.mdx"]))
 
-    relationships = data_scope.add_collector()
+    document_node = data_scope.add_collector()
+    entity_relationship = data_scope.add_collector()
+    entity_mention = data_scope.add_collector()
 
     with data_scope["documents"].row() as doc:
         doc["chunks"] = doc["content"].transform(
             cocoindex.functions.SplitRecursively(),
             language="markdown", chunk_size=10000)
 
+        doc["summary"] = doc["content"].transform(
+            cocoindex.functions.ExtractByLlm(
+                llm_spec=cocoindex.LlmSpec(
+                    api_type=cocoindex.LlmApiType.OPENAI, model="gpt-4o"),
+                output_type=DocumentSummary,
+                instruction="Please summarize the content of the document."))
+        document_node.collect(
+            filename=doc["filename"], title=doc["summary"]["title"],
+            summary=doc["summary"]["summary"])
+
         with doc["chunks"].row() as chunk:
             chunk["relationships"] = chunk["text"].transform(
                 cocoindex.functions.ExtractByLlm(
@@ -59,7 +76,7 @@ def docs_to_kg_flow(flow_builder: cocoindex.FlowBuilder, data_scope: cocoindex.D
                 relationship["object_embedding"] = relationship["object"].transform(
                     cocoindex.functions.SentenceTransformerEmbed(
                         model="sentence-transformers/all-MiniLM-L6-v2"))
-                relationships.collect(
+                entity_relationship.collect(
                     id=cocoindex.GeneratedField.UUID,
                     subject=relationship["subject"],
                     subject_embedding=relationship["subject_embedding"],
@@ -67,9 +84,23 @@ def docs_to_kg_flow(flow_builder: cocoindex.FlowBuilder, data_scope: cocoindex.D
                     object_embedding=relationship["object_embedding"],
                     predicate=relationship["predicate"],
                 )
-
-    relationships.export(
-        "relationships",
+                entity_mention.collect(
+                    id=cocoindex.GeneratedField.UUID, entity=relationship["subject"],
+                    filename=doc["filename"], location=chunk["location"],
+                )
+                entity_mention.collect(
+                    id=cocoindex.GeneratedField.UUID, entity=relationship["object"],
+                    filename=doc["filename"], location=chunk["location"],
+                )
+    document_node.export(
+        "document_node",
+        cocoindex.storages.Neo4j(
+            connection=conn_spec,
+            mapping=cocoindex.storages.Neo4jNode(label="Document")),
+        primary_key_fields=["filename"],
+    )
+    entity_relationship.export(
+        "entity_relationship",
         cocoindex.storages.Neo4j(
             connection=conn_spec,
             mapping=cocoindex.storages.Neo4jRelationship(
@@ -107,6 +138,25 @@ def docs_to_kg_flow(flow_builder: cocoindex.FlowBuilder, data_scope: cocoindex.D
         ),
         primary_key_fields=["id"],
     )
+    entity_mention.export(
+        "entity_mention",
+        cocoindex.storages.Neo4j(
+            connection=conn_spec,
+            mapping=cocoindex.storages.Neo4jRelationship(
+                rel_type="MENTION",
+                source=cocoindex.storages.Neo4jRelationshipEnd(
+                    label="Document",
+                    fields=[cocoindex.storages.Neo4jFieldMapping("filename")],
+                ),
+                target=cocoindex.storages.Neo4jRelationshipEnd(
+                    label="Entity",
+                    fields=[cocoindex.storages.Neo4jFieldMapping(
+                        field_name="entity", node_field_name="value")],
+                ),
+            ),
+        ),
+        primary_key_fields=["id"],
+    )
 
 @cocoindex.main_fn()
 def _run():
diff --git a/python/cocoindex/storages.py b/python/cocoindex/storages.py
index e2e58342..c1568e2e 100644
--- a/python/cocoindex/storages.py
+++ b/python/cocoindex/storages.py
@@ -63,7 +63,7 @@ class Neo4jRelationship:
     rel_type: str
     source: Neo4jRelationshipEnd
     target: Neo4jRelationshipEnd
-    nodes: dict[str, Neo4jRelationshipNode]
+    nodes: dict[str, Neo4jRelationshipNode] | None = None
 
 class Neo4j(op.StorageSpec):
     """Graph storage powered by Neo4j."""
diff --git a/src/ops/storages/neo4j.rs b/src/ops/storages/neo4j.rs
index 03da3f20..bb582d59 100644
--- a/src/ops/storages/neo4j.rs
+++ b/src/ops/storages/neo4j.rs
@@ -56,7 +56,7 @@ pub struct RelationshipSpec {
     rel_type: String,
     source: RelationshipEndSpec,
     target: RelationshipEndSpec,
-    nodes: BTreeMap<String, RelationshipNodeSpec>,
+    nodes: Option<BTreeMap<String, RelationshipNodeSpec>>,
 }
 
 #[derive(Debug, Deserialize)]
@@ -693,7 +693,7 @@ impl RelationshipSetupState {
                         rel_spec.rel_type
                     )
                 })?;
-                for (label, node) in rel_spec.nodes.iter() {
+                for (label, node) in rel_spec.nodes.iter().flatten() {
                     sub_components.push(ComponentState {
                         object_label: ElementType::Node(label.clone()),
                         index_def: IndexDef::KeyConstraint {
@@ -720,7 +720,13 @@ impl RelationshipSetupState {
                         });
                     }
                 }
-                dependent_node_labels.extend(rel_spec.nodes.keys().cloned());
+                dependent_node_labels.extend(
+                    rel_spec
+                        .nodes
+                        .iter()
+                        .flat_map(|nodes| nodes.keys())
+                        .cloned(),
+                );
             }
         };
         Ok(Self {
@@ -1069,7 +1075,8 @@ impl<'a> DependentNodeLabelAnalyzer<'a> {
                 .collect(),
             index_options: rel_spec
                 .nodes
-                .get(&rel_end_spec.label)
+                .as_ref()
+                .and_then(|nodes| nodes.get(&rel_end_spec.label))
                 .and_then(|node_spec| Some(&node_spec.index_options)),
         })
     }