OntoDB

A database management system for ontologies. Data is RDF and the query language is SPARQL. The shell answers a SPARQL subset over B+ tree indexes with a cost-based optimizer, runs statements under strict two-phase locking, and recovers pages with ARIES after a crash. It also does semantic search: a class hierarchy becomes integer intervals in a B+ tree, and vectors are searched by exact, IVF, or HNSW indexes, optionally limited to the terms under a class.

Build

# Ubuntu
sudo apt-get install -y clang cmake ninja-build pkg-config libraptor2-dev
# macOS
brew install pkgconf raptor cmake ninja

cmake --preset dev && cmake --build --preset dev

Presets are dev (AddressSanitizer and UndefinedBehaviorSanitizer), tsan, and release. ./build/dev/ontodb_test runs the tests. Every push runs the suite under ASan/UBSan and ThreadSanitizer, then checks formatting and clang-tidy.

Run

$ ./build/dev/ontodb mydb
OntoDB> \load data/tiny.owl
loaded 14 triples in 5.2 ms
OntoDB> SELECT ?kind WHERE { ?kind <http://www.w3.org/2000/01/rdf-schema#subClassOf> <http://example.org/materials#Material> . }
?kind
<http://example.org/materials#Metal>
<http://example.org/materials#Polymer>
(2 rows)
OntoDB> \verify
verify: ok

Pass a directory (ontodb mydb) to keep the database on disk: every update statement and every \load is a transaction, forced to a checksummed write-ahead log before the prompt returns, and reopening the directory replays the committed ones. Without a directory the shell is an in-memory database. A query may span lines and runs when its braces close; \help lists the commands and \explain prints the plan.

Documentation

• Manual — https://lamng3.com/ontodb/ (installation, tutorial, shell and SPARQL reference, internals), with an in-browser playground.
• Design notes and roadmap — the project wiki.

The book, OntoDB: Database Internals by Example (PDF), and two papers — a fast and persistent query engine and hierarchy-filtered vector search — are in docs/.

License

BSD 3-Clause. Copyright (c) 2026 Lam Nguyen.