Domain Decomposition, Graph Ownership, Shared Reference Data, and Governance Across Graphs

AtlasMart can technically split Catalog, Customers and Orders, but technology does not decide who may change productId, how a Product rename propagates, which domain may retain customer PII, or who restores a constituent after corruption. Without governance, proxy IDs drift, duplicated fields become contradictory, and a “federated graph” becomes three incompatible schemas. This lesson makes ownership executable.

Learning outcomes

Reproducible Chapter 19 lab baseline

1. Domain decomposition starts from invariants

2. Identity governance is the federation backbone

3. Shared reference data has four strategies

4. Security is per boundary

Optional Enterprise composite RBAC does not create one blanket privilege over every constituent. Access to the composite and each target database must be granted appropriately. For remote aliases, the remote DBMS applies the remote principal’s permissions. Data-domain governance should therefore publish a matrix of service identity → composite access → constituent access → graph operations → procedures.

// OPTIONAL Enterprise example; exact role naming is an AtlasMart design choice.
CYPHER 25
CREATE ROLE atlasmart_reader IF NOT EXISTS;
GRANT ACCESS ON DATABASE atlasmart TO atlasmart_reader;
GRANT ACCESS ON DATABASE `atlasmart-catalog` TO atlasmart_reader;
GRANT ACCESS ON DATABASE `atlasmart-orders` TO atlasmart_reader;
GRANT ACCESS ON DATABASE `atlasmart-customers` TO atlasmart_reader;
GRANT MATCH {*} ON GRAPH `atlasmart-catalog` TO atlasmart_reader;
GRANT MATCH {*} ON GRAPH `atlasmart-orders` TO atlasmart_reader;
GRANT MATCH {*} ON GRAPH `atlasmart-customers` TO atlasmart_reader;
SHOW ROLE atlasmart_reader PRIVILEGES;

5. Schema and version changes need compatibility windows

6. Backup/recovery is domain-owned and reconciled

7. Reconciliation query set

CYPHER 25
MATCH (cr:CustomerRef)<-[:PLACED_BY]-(o:Order)
RETURN cr.customerId AS customerId, count(o) AS orderCount
ORDER BY customerId;

MATCH (pr:ProductRef)<-[li:CONTAINS]-(o:Order)
RETURN pr.productId AS productId,
       count(li) AS lineCount,
       sum(li.quantity) AS units
ORDER BY productId;

# Pseudocode deliberately uses stable business IDs, not element IDs.
owner_product_ids = set(fetch_catalog_product_ids())
proxy_product_ids = set(fetch_order_product_ref_ids())
print("missing in catalog", sorted(proxy_product_ids - owner_product_ids))
print("unused in orders", sorted(owner_product_ids - proxy_product_ids))
# A difference is evidence to classify, not automatically an error: tombstones/history may be valid.

8. Governance acceptance checklist

Production judgment

Summary and next step

Domain boundaries are now backed by owners, IDs, copy semantics, privileges, versions and recovery rules. Lesson 5 combines the chapter into an architecture review that decides which AtlasMart relationships stay local, which become federated references, and when the split should be rejected.

Authoritative references

• Current Neo4j versions — Current self-managed release 2026.07.1 and 5.26.30 LTS snapshot.
• Database administration — Current database/transaction-domain model and the one-standard-database Community versus multi-database Enterprise boundary.
• Create standard databases — Enterprise-only self-managed CREATE DATABASE semantics and system-database administration.
• Show databases — SHOW DATABASES fields including type, role, writer, status, aliases and constituents.
• Composite database concepts — Enterprise-only, unavailable-on-Aura composite semantics, local/remote constituents, compatibility, transactions and proxy-node federation.
• Create composite databases — CREATE COMPOSITE DATABASE and current default Cypher language behavior.
• Query composite databases — USE/CALL graph selection, graph functions, update restrictions, root-scope limits and runtime behavior.
• Composite aliases — Local and remote constituent aliases, SHOW ALIASES evidence, namespace rules and alias limitations.
• Standard aliases — Local/remote alias behavior, credentials, access visibility and current OIDC-forwarding option for remote aliases.
• Composite RBAC — Access must be granted to the composite and constituents; remote constituents enforce remote-user RBAC.
• Composite tutorial — Official federation/sharding example and proxy-node model.
• Database alias command syntax — Current SHOW/CREATE/ALTER alias command forms.
• Cypher USE clause — Current graph-selection clause semantics for composite/federated queries.
• Python driver manual — Official driver lifecycle, sessions, parameters, database selection and application-side orchestration.
• Backup and restore — Operational reminder that constituent data stores—not a composite alias layer—are the recovery units.