A browser-based ontology workbench built with Streamlit and rdflib
Try it now: orionbelt.streamlit.app
OrionBelt lets you build, edit, and maintain OWL ontologies and SKOS vocabularies in your browser. No Java, no desktop install - just pip install and go.
It works with OWL ontologies (classes as owl:Class, properties as owl:ObjectProperty / owl:DatatypeProperty). Pure RDFS vocabularies like schema.org that use rdfs:Class and rdf:Property are not currently surfaced in the Classes / Properties panels.
It's not trying to be Protégé. It's meant for people who want something lighter: a workbench that's easy to pick up, hard to break things with, and good enough for real ontology work.
Not losing your work. Every change creates an undo checkpoint. Deletes show you what will break before you confirm. Imports show a diff so you can review before applying.
Keeping your ontology clean. Validation catches orphan classes, duplicate labels, domain/range mismatches, missing annotations, and SKOS-specific issues like broader/narrower cycles. Not just "you have warnings" but "here's what's wrong and where."
Moving fast in large ontologies. Global search across everything. Usage/backlink views for any resource. Click a node in the graph and jump straight to the editor. Bulk add/edit/delete so you're not filling out forms one entity at a time.
Working with others. Merge-aware imports with three strategies (replace, merge, merge-overwrite). Conflict detection. Prefix reconciliation. Change reports you can download. You can actually review what an import would do before committing it.
Full CRUD for classes, object/data properties, individuals, restrictions, relations, and annotations. Hierarchy management, rename with reference updates, and tabbed editing per entity type.
Every entity page has a Bulk Operations tab:
- Add - paste names (one per line) or CSV with headers like
Name, Label, Parent - Edit - spreadsheet view of all entities with editable labels, comments, parents
- Delete - multi-select and remove in one go
Annotations have their own bulk editor with per-row add/delete actions.
A dedicated page for building controlled vocabularies:
- Concept schemes with concept counts
- Concepts with prefLabel, definition, broader/narrower (inverses auto-managed)
- Hierarchy tree view, filterable by scheme
- Full SKOS relation support (broader, narrower, related, all match types)
- SKOS validation: missing prefLabels, orphans, duplicate labels, cycles
Five starter templates you can merge into or replace your current ontology: Organization, Product Catalog, Event, Person/Contact, and SKOS Thesaurus. Each is a valid Turtle snippet with a preview before you apply it.
Start from a professionally built upper ontology instead of redefining foundational concepts for every project. Two options ship in the box:
- gist by Semantic Arts — a minimalist upper ontology covering ~100 classes (Event, Person, Organization, Agreement, Specification, etc.) and ~100 properties. Select which modules to load (Core, RDFS Annotations, SubClass Assertions, Media Types) and merge or replace your current ontology.
- gUFO (gentle UFO) — a lightweight OWL implementation of the Unified Foundational Ontology, suitable for OntoUML-style conceptual modeling with kinds, roles, phases, events, situations, qualities, and relators.
A separate tab for importing widely-used domain and reference vocabularies. The loader supports both bundled vocabularies (instant) and on-demand downloads (verified against a pinned SHA256 and cached on disk). Currently ships with PROV-O, FOAF, and GoodRelations — all bundled.
| Format | Extension | Import | Export |
|---|---|---|---|
| Turtle | .ttl | ✅ | ✅ |
| RDF/XML | .owl, .rdf | ✅ | ✅ |
| N-Triples | .nt | ✅ | ✅ |
| N3 | .n3 | ✅ | ✅ |
| JSON-LD | .jsonld | ✅ | ✅ |
Imports on an empty ontology go straight through. Otherwise you get a review panel: diff summary, conflict table, prefix changes, import mode selector, and a downloadable change report.
- Missing labels, domains, ranges
- Orphan classes, duplicate labels, domain/range mismatches
- Untyped individuals
- SKOS checks (see above)
- RDFS and OWL-RL reasoning via owlrl
Interactive vis-network graph with class filtering, configurable node limits, click-to-navigate into the editor, hierarchy tree view, and statistics charts.
- Full undo/redo with labeled checkpoints
- Delete impact analysis before confirmation
- Bulk operations create a single undo point
- Namespace prefix management from the Dashboard
# Clone and install
git clone https://github.com/ralforion/orionbelt-ontology-builder.git
cd orionbelt-ontology-builder
pip install -r requirements.txt
# Or install from PyPI
pip install orionbelt-ontology-builder
# Run
streamlit run app.py| Page | What it does |
|---|---|
| Dashboard | Metadata, base URI, statistics, prefix management, validation |
| Classes | Class hierarchy, CRUD, bulk operations |
| Properties | Object & data properties, CRUD, bulk operations |
| Individuals | Instance management, property assertions, bulk operations |
| Relations | Class, property, and individual relations |
| Restrictions | OWL restrictions and cardinality constraints |
| Advanced | Advanced OWL features |
| Annotations | RDFS, SKOS, Dublin Core annotations with bulk editing |
| SKOS Vocabulary | Concept schemes, concepts, hierarchy, SKOS validation |
| Import / Export | File import with merge review, export, new ontology, templates |
| Source | Live Turtle source view of the ontology |
| Validation | Ontology validation and OWL reasoning |
| Visualization | Interactive graph (OWL + SKOS), hierarchy tree, statistics |
orionbelt-ontology-builder/
├── app.py # Streamlit Cloud entry point (delegates to package)
├── ontology_manager.py # Backward-compat shim
├── templates.py # Backward-compat shim
├── orionbelt_ontology_builder/ # The actual installable package
│ ├── app.py # Streamlit UI
│ ├── ontology_manager.py # Core OWL/SKOS engine (rdflib)
│ ├── templates.py # Built-in templates / upper / reference ontologies
│ ├── samples/ # Bundled gist, gUFO, FOAF, PROV-O, GoodRelations, …
│ ├── lib/ # Frontend libraries (vis-network, Tom Select)
│ ├── assets/ # Logos and screenshots
│ └── favicon.png
├── pyproject.toml # Project metadata
└── tests/ # pytest suite
Dependencies: streamlit, rdflib, owlrl, networkx, pyvis.
An ontology-based MCP server that analyzes relational database schemas (PostgreSQL, Snowflake, Dremio) and generates RDF/OWL ontologies with embedded SQL mappings. Together with the Ontology Builder, they form a toolkit for ontology-driven data modeling.
Copyright 2025 RALFORION d.o.o.
Licensed under the Business Source License 1.1. The Licensed Work will convert to Apache License 2.0 on 2030-03-30.
By contributing to this project, you agree to the Contributor License Agreement.
