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owlready2

A package for ontology-oriented programming in Python: load OWL 2.0 ontologies as Python objects, modify them, save them, and perform reasoning via HermiT. Includes an optimized RDF quadstore.

With conditionsPyPI Python ModulesReleased Jun 202696.8K downloads / moLGPL-3.0-or-laterSource build
PyPI

Decision gist · record as of 2026-08-14

sdist only — owlready2-0.51.tar.gz · builds from source
v0.51 · released 2026-06-22 · Python >=3.6

Yes, with conditions. Owlready2 is production-stable, actively maintained, and solves a specific problem—ontology-oriented programming in Python. The copyleft LGPL-3.0-or-later license is acceptable for most open-source projects but requires review for proprietary use. High install friction (source-only distribution requiring compilation) is a real barrier; ensure your environment has a C compiler and development headers. If you need OWL/RDF manipulation, semantic reasoning, or knowledge graph management in Python, it is worth the setup cost.AI-flagged interpretation of the facts on this page — verify before relying

Before you install

  • Requires compilation from source (tar.gz); ensure a C compiler and development headers are available.
  • High install friction due to source-only distribution (tar.gz); requires compilation.
  • Actively maintained with recent release (53 days old) and production-stable status, supporting Python 3.6–3.10 and PyPy.

License · maintenance · safety

LGPL-3.0-or-later (copyleft) — Licensed under LGPL-3.0-or-later (copyleft). Derivative works and modifications must be distributed under the same license; proprietary use requires careful review of linking obligations.

last release 2026-06-22 (53 days)

0 known vulnerabilities (OSV.dev, 2026-08-14) · 96,791 downloads/mo, #13,193 on PyPI

Alternatives

owlrlImplements OWL2 RL Profile and RDFS inference on top of rdflib using forward-chaining rules to derive new triples.pure-Python wheel1.1M/mo rdflibRDFLib is a Python library for parsing, querying, and serializing RDF data across multiple formats including RDF/XML.pure-Python wheel22.0M/mo prontoPronto parses, browses, creates, and exports ontologies in OBO, OBO Graphs JSON, and OWL2 RDF/XML formats.pure-Python wheel142.9K/mo

Verify before relying

from owlready2 import *
onto = get_ontology("http://example.org/ontology.owl")
onto.load()
results = list(default_world.sparql("SELECT * { ?x a owl:Class . }"))
  • Whether the included HermiT and Pellet reasoners are fully functional or require external setup.
  • Performance characteristics and scalability limits beyond the stated 1 billion RDF triples claim.
  • Whether PyMedTermino2 submodule for UMLS/DBpedia requires additional dependencies or configuration.
Same gist for agents: .md · .json

What it is and what it does

Owlready2 is a Python framework for working with OWL 2.0 ontologies and RDF knowledge graphs as if they were native Python objects. It provides transparent manipulation of ontology classes, instances, and properties, automatic reasoning and classification via embedded reasoners, and an optimized quadstore backend that can handle large-scale RDF datasets. The package supports multiple serialization formats (NTriples, RDF/XML, OWL/XML), SPARQL querying, and can be used as an object-relational mapper for graph-based data storage.

The module is designed for knowledge representation and semantic reasoning tasks, particularly in biomedical and scientific domains. It includes built-in support for medical terminologies through PyMedTermino2, allows mixing OWL constructs with Python methods on classes, and integrates with RDFlib. The main constraint is that it distributes as source code only, requiring compilation during installation.

Use it for

  • Load and programmatically manipulate biomedical ontologies (UMLS, SNOMED CT) for terminology mapping and knowledge extraction.
  • Build semantic knowledge graphs by creating OWL classes and instances in Python, then export to standard RDF/XML formats.
  • Query and reason over large RDF datasets using SPARQL and automatic classification with HermiT or Pellet reasoners.
  • Use as a graph database alternative for ontology-backed object storage with semantic reasoning capabilities.
  • Integrate OWL-based domain models into Python applications while maintaining OWL 2.0 compliance and reasoning.

Worth the install?

AI-flagged interpretation of the facts on this page. Verify before relying on it.

With conditions

Yes, with conditions.

Owlready2 is production-stable, actively maintained, and solves a specific problem—ontology-oriented programming in Python. The copyleft LGPL-3.0-or-later license is acceptable for most open-source projects but requires review for proprietary use. High install friction (source-only distribution requiring compilation) is a real barrier; ensure your environment has a C compiler and development headers. If you need OWL/RDF manipulation, semantic reasoning, or knowledge graph management in Python, it is worth the setup cost.

Install

owlready2 on PyPI

Before you install

High install friction due to source-only distribution (tar.gz); requires compilation. Actively maintained with recent release (53 days old) and production-stable status, supporting Python 3.6–3.10 and PyPy.

Requires compilation from source (tar.gz); ensure a C compiler and development headers are available.

License in practice

Licensed under LGPL-3.0-or-later (copyleft). Derivative works and modifications must be distributed under the same license; proprietary use requires careful review of linking obligations.

Quickstart

from owlready2 import *
onto = get_ontology("http://example.org/ontology.owl")
onto.load()
results = list(default_world.sparql("SELECT * { ?x a owl:Class . }"))

Verify before relying

  • Whether the included HermiT and Pellet reasoners are fully functional or require external setup.
  • Performance characteristics and scalability limits beyond the stated 1 billion RDF triples claim.
  • Whether PyMedTermino2 submodule for UMLS/DBpedia requires additional dependencies or configuration.

Package facts

LicenseLGPL-3.0-or-later copyleft
Python supportSupports the current Python release >=3.6
Install frictionHigh. Source build required
Runtime dependenciesNone
MaintenanceActively maintained 53 days since the last release
First released
Downloads96,791 / month, #13,193 on PyPI 30-day window, as of 2026-08-14
Known vulnerabilitiesNone known OSV.dev, checked 2026-08-14
Classifiers
Development Status :: 5 - Production/StableIntended Audience :: DevelopersIntended Audience :: Information TechnologyIntended Audience :: Science/ResearchOperating System :: OS IndependentProgramming Language :: Python :: 3Programming Language :: Python :: 3 :: OnlyProgramming Language :: Python :: 3.10Programming Language :: Python :: 3.6Programming Language :: Python :: 3.7Programming Language :: Python :: 3.8Programming Language :: Python :: 3.9Programming Language :: Python :: Implementation :: CPythonProgramming Language :: Python :: Implementation :: PyPyTopic :: Scientific/Engineering :: Artificial IntelligenceTopic :: Software Development :: Libraries :: Python Modules

Evidence: owlready2-0.51.tar.gz

Tags

Capabilities
OWL ontology PythonRDF quadstoresemantic reasoning Pythonknowledge graph managementontology-oriented programmingOWL 2.0 loaderSPARQL queries Python
Topics
ontology-reasoningknowledge-graphssemantic-web

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See also owlrl · rdflib · pronto · pyshacl · SPARQLWrapper · pymantic · pystardog · PyShEx · CFGraph · sssom