Languages & Standards
7 entriesW3C and community languages for modelling and querying knowledge.
01OWL 2 Web Ontology LanguageThe W3C language for authoring ontologies: classes, properties, individuals and axioms with description-logic semantics, so a reasoner can infer new facts and check consistency.
02RDF Schema (RDFS)The lightweight vocabulary layer of RDF: classes, subclass and sub-property hierarchies, and property domains and ranges. Often all the schema a knowledge graph needs.
03SKOSA W3C model for publishing thesauri, taxonomies and controlled vocabularies as linked data, using concepts, broader/narrower links and labels.
04SHACLThe W3C Shapes Constraint Language for validating RDF graphs against a set of shapes — the usual way to enforce data quality on top of an ontology.
05SPARQL 1.1The W3C query language and protocol for RDF, used to query ontology-based data and, with entailment regimes, inferred triples.
06JSON-LD 1.1A JSON serialization of linked data whose context maps plain JSON keys onto ontology terms, bridging web APIs and knowledge graphs.
07LinkMLA YAML-based modeling language for defining schemas and ontologies, with generators that produce OWL, SHACL, JSON Schema and other artifacts from one source.
Editors & Visualization
4 entriesTools for building and viewing ontologies.
08ProtégéThe free, open-source ontology editor and framework from Stanford. Supports OWL 2, reasoner integration and a large plugin ecosystem; the default tool for building ontologies.
09WebProtégéA web-based, collaborative ontology editor from Stanford, with shared editing, change tracking and discussion for ontology teams.
10VocBenchA collaborative web application for editing OWL ontologies, SKOS thesauri and RDF datasets with workflow and validation support.
11WebVOWLA web application for visualizing ontologies as interactive node-link diagrams, useful for exploring and explaining ontology structure.
Reasoners, Libraries & Tooling
9 entriesSoftware for reasoning over and programming with ontologies.
12HermiTAn OWL 2 DL reasoner for Java that checks consistency, classifies ontologies and computes entailments.
13OpenlletAn open-source OWL 2 DL reasoner for Java, continuing the Pellet line, with Jena and OWL API integrations. Its latest GitHub release, 2.6.5, dates from September 2019, so check its activity.
14ELK ReasonerA fast reasoner for the OWL 2 EL profile, designed for very large biomedical-style ontologies. Its latest GitHub release, 0.6.0, dates from May 2024.
15OWL APIThe Java API and reference implementation for creating, manipulating and serializing OWL ontologies. GitHub lists 5.5.1 (September 2024) as the latest release.
16Apache JenaA Java framework for semantic web and linked data applications: RDF and ontology APIs, SPARQL, rule and OWL inference, and the Fuseki server.
17Owlready2A Python module for ontology-oriented programming: load OWL ontologies, manipulate classes and individuals as Python objects, and run reasoners.
18RDFLibA Python library for working with RDF: parsing, serializing, graph manipulation and SPARQL queries.
19ROBOTA command-line tool for automating ontology development workflows — merging, reasoning, templating, quality checks and release. GitHub lists v1.9.11 (October 2026) as the latest release.
20OntopA virtual knowledge graph system that maps relational databases to ontologies and rewrites SPARQL queries into SQL, without copying data.
Repositories & Domain Ontologies
7 entriesReusable ontologies and where to find them.
21BioPortalA large repository and browser of biomedical ontologies, with search, mappings and ontology metadata.
22OBO FoundryA community of ontology developers committed to shared principles for interoperable, reusable life-science ontologies.
23EBI Ontology Lookup ServiceA repository and browsing service for biomedical ontologies, with search and an API for looking up terms.
24Schema.orgA shared vocabulary of types and properties for structured data on the web, widely used in JSON-LD and search-engine markup.
25FIBOThe Financial Industry Business Ontology from the EDM Council, defining shared concepts for financial instruments, entities and contracts.
26Gene OntologyThe widely used ontology of gene function, describing molecular functions, biological processes and cellular components.
27Basic Formal Ontology (BFO)A top-level ontology used as a common upper layer by many domain ontologies, especially in biomedicine.
Enterprise Semantic Platforms
3 entriesCommercial platforms with ontology and reasoning support.
28StardogA knowledge graph platform with OWL reasoning, SHACL constraint validation and virtual graphs over existing data sources.
29TopBraid EDGTopQuadrant's enterprise data governance platform for managing ontologies, taxonomies and shapes as shared, governed models.
30PoolParty (now part of Graphwise)Semantic middleware for taxonomies, ontologies and knowledge graphs; poolparty.biz now presents it as part of the Graphwise platform.
More Ontology Repositories, Tools & Foundations
5 entriesRepositories, upper ontologies and tooling.
Automatic Ontology Generation & Agent Context Layers
8 entriesTools and research that build ontologies and semantic layers from data and text with LLMs, led by NVIDIA Auto Ontology.
36NVIDIA Auto OntologyNVIDIA's open-source Python framework (Apache-2.0) that generates an enterprise ontology and semantic layer from database metadata, reconciles definitions across systems, grounds text-to-SQL agents in certified business meaning and returns provenance with every answer. It serves context through MCP, CLI and API, runs on Postgres with pgvector and NVIDIA NIM models, and ships a web UI with RBAC. Currently not accepting outside contributions; benchmark results are not published in the README.
37Auto Ontology Evaluation ToolkitNVIDIA's companion toolkit for text-to-SQL evaluation of Auto Ontology, including a script that seeds the Wide World Importers sample database. Use it to run benchmarks such as BIRD yourself.
38Auto Ontology MCP Server (community)Community project that exposes Auto Ontology's semantic layer and a personal knowledge base as an MCP server for Claude, ChatGPT and other MCP clients. Not an NVIDIA project; review it before use.
39End-to-End Ontology Learning with Large Language Models (OLLM)NeurIPS 2024 paper on building the taxonomic backbone of an ontology from scratch with an LLM, with metrics for comparing generated and reference ontologies.
40Ontology Generation using Large Language Models (Ontogenia)Study of prompting methods that draft OWL ontologies from user stories and competency questions, compared against novice ontology engineers.
41OntoGPTMonarch Initiative toolkit for LLM-based ontological extraction, including schema-guided extraction with LinkML.
42BIRD Text-to-SQL BenchmarkLarge benchmark of text-to-SQL over real databases, the kind of test Auto Ontology's evaluation repo points to.
43Spider 2.0Enterprise-scale text-to-SQL benchmark with real workflows and large schemas.
Related Pages
5 entriesRelated directories on this site.
44Knowledge Graphs (KGs)Knowledge graph platforms and standards.
45Knowledge Graphs & Graph TechnologiesGraph databases, ontologies and GNNs.
46RDF Graph Databases & Semantic GraphsRDF stores and semantic graph databases.
47Graph DatabasesGraph database systems.
48Graph Data PlatformsGraph analytics and managed services.
Frequently Asked Questions
What is an ontology?
In computing, an ontology is a formal, shared specification of the concepts in a domain and the relationships between them, usually expressed in a language such as OWL so machines can reason over it.
What is the difference between RDFS, OWL and SKOS?
RDFS gives basic classes and properties, OWL adds richer logic for reasoning, and SKOS models thesauri and taxonomies with looser semantics.
Which editor should I use?
Protégé is the long-standing open-source standard; WebProtégé and VocBench support collaborative editing in the browser.
What does SHACL do?
SHACL validates RDF graphs against shapes, checking that data conforms to expected structure, complementing OWL's inference.
How do ontologies relate to knowledge graphs?
Ontologies supply the schema and meaning for a knowledge graph; see the Knowledge Graphs and Semantic Graphs pages for platforms that store and query them.