OntoL-Manage 8.1: Switch Graph Databases by Config, Not Code

Problem: Hidden Coupling to Memgraph

OntoL-Manage's query layer emits openCypher, but before 8.1 the system was tightly coupled to Memgraph in three places:

Constraint DDL : Startup created unique constraints for GeneratedOntology using Neo4j 3.x legacy syntax, which fails on Neo4j 4/5 and was silently swallowed as a warning, leaving constraints missing.

Date dialect : Inference rules using date_diff, days_since, days_until relied on Memgraph's timestamp(date()) microsecond semantics, which do not execute on Neo4j.

Lock timestamp : Memgraph uses microseconds while Neo4j uses milliseconds, causing semantic mismatch.

Solution: Dialect Layer with Two Registrable Hooks

Version 8.1 introduces a graph_dialect layer that converges the three coupling points into two registrable hooks — a constraint DDL template and date expression mappings. Adding a new graph database now only requires registering a dialect implementation without touching the query layer or reasoning engine.

Configuration

Switching is controlled by a single environment variable:

GRAPH_DB_TYPE=neo4j   # default memgraph, behavior identical to 8.0
NEO4J_URI=bolt://127.0.0.1:7687
NEO4J_USER=ontoll
NEO4J_PASSWORD=*****

The default memgraph setting preserves byte-for-byte compatibility with 8.0, enabling zero-change upgrades for existing deployments.

Migration Procedure

ontoll admin export

— full export of ontology (schema, DSL rules, instances, indexes).

Update configuration to target the new backend. ontoll admin import — import into the new database.

Validate against the acceptance checklist.

Release Gate Criteria

Memgraph regression : Default-path Cypher must be byte-for-byte identical to 8.0.

Neo4j 5.x smoke test : Constraints create successfully, DSL date rules execute, lock timestamp unit is correct.

Dialect extensibility : New databases require only registering the two hooks — already implemented via registration-based design.

Known Boundaries

Private extensions (APOC/Mage) prevent direct switching.

Performance baselines must be rebuilt after switching.

Downtime is required during the switch window; zero-downtime migration is planned for a future release.

Conclusion

8.1 reduces backend switching from an engineering effort to a single configuration item, and the dialect layer architecture guarantees constant integration cost for any third graph database. Release is gated on the first two acceptance criteria being verified and recorded.