Ontology Hub

A web application to explore, search, and reuse RDF ontologies and vocabularies (inspired by LOV), built with Node.js. It provides a catalog, advanced search, and integration with ingestion and metadata validation processes.

Table of Contents

• Context and Purpose
• Key Features
• Architecture
• Requirements
• Installation
• Configuration
• Running the Application
• Frontend with Pug (SSR)
• NPM Scripts
• API Examples
• Repository Structure
• Ingestion and Indexing
• Docker Usage
• Testing
• How to Contribute
• Roadmap
• Acknowledgments and Funding
• Authors and Contact
• License

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Context and Purpose

Ontology Hub centralizes metadata for ontologies and vocabularies (RDF/OWL/RDFS/SKOS), making them easier to discover and reuse. It includes a catalog, faceted search, version views, and API endpoints for integration.

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Key Features

• 🔎 Search and facets by name, prefix, terms, author, license, topics (SKOS), etc.
• 📚 Ontology catalog with versions, changes, and documentation links.
• 🧩 Prefix and URI resolution.
• 🛠️ Metadata ingestion from RDF/JSON/TTL files.
• ⚡ Indexing in Elasticsearch for fast responses.
• 🔐 REST API for querying and exporting results (JSON/CSV/NDJSON).
• 📈 Statistics (vocabulary usage, classes/properties, popularity).

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Architecture

• Backend: Node.js + Express
• Frontend: Pug (SSR with Express)
• Database: MongoDB
• Search Engine: Elasticsearch

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Requirements

• Node.js 18+ (20 LTS recommended)
• npm or pnpm
• MongoDB 6+
• Elasticsearch 9.2+
• Apache Jena
• Python 3

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Installation

1. Clone the repository:

   git clone https://github.com/ProyectoPIONERA/Ontology-Hub.git
   cd Ontology-Hub

2. Install dependencies:

   npm install

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Configuration

Create a .env file in the root directory with variables like:

NODE_ENV=development
PORT=3000
BASE_URL=http://localhost:3000
MONGO_URI=mongodb://localhost:27017/ontologyhub
ES_NODE=http://localhost:9200
ES_USERNAME=elastic
ES_PASSWORD=OntologyHub2026
ES_INDEX=vocabs
REDIS_URL=redis://localhost:6379
JWT_SECRET=please_change_me
ALLOW_ORIGIN=*

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Running the Application

npm start

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Repository Structure

ontology-hub-node/
├── app/
│   ├── views/        # Pug templates
│   ├── public/       # Static assets
├── config/
├── scripts/
├── dockers/
├── jena/
├── lib/
├── setup/
├── versions/
├── vocommons/
├── server.js
├── Dockerfile
├── DockerfileELS
├── docker-compose.yml
├── package.json
└── README.md

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Docker Usage

This project includes Docker support for quick setup and deployment.

1. Build and Run with Docker Compose

docker-compose up --build

This will start:

• Node.js app
• MongoDB
• Elasticsearch
• Optional services like Jena if configured.

Linux Docker DNS Troubleshooting

On some native Linux hosts, the Docker build container may fail to resolve external hosts while building the lov_server image. This is usually an environment-level Docker networking or DNS issue, not an application error.

Typical symptoms include failures while cloning external repositories:

fatal: unable to access 'https://github.com/ProyectoPIONERA/Ontology-Hub-Scripts.git/':
Could not resolve host: github.com

or while downloading Apache Jena/Fuseki dependencies:

Resolving archive.apache.org (archive.apache.org)... failed:
Temporary failure in name resolution.
wget: unable to resolve host address 'archive.apache.org'

The affected build steps are:

• cloning Ontology-Hub-Scripts during the Maven build stage;
• cloning GrOwEr during the final image stage;
• downloading Apache Jena and Fuseki archives from archive.apache.org at container startup if they are not already present in /app/jena.

If this happens, first verify DNS from both the host and Docker:

docker run --rm alpine nslookup github.com
docker run --rm alpine nslookup archive.apache.org

If Docker DNS is failing, check the Docker daemon DNS configuration, corporate VPN/proxy settings, firewall rules, or /etc/resolv.conf. After fixing DNS, rebuild the image:

docker compose build --no-cache lov_server
docker compose up -d

If the image was already built successfully and only the runtime service is unstable, you can restart the app service manually with exposed ports:

docker compose ps
docker compose stop lov_server
docker compose run --rm --service-ports --entrypoint node lov_server server.js

Then return the service to normal Compose management:

docker compose ps -a
docker compose up -d lov_server
docker compose logs -f lov_server

Use this workaround only after the image exists locally. If the image build failed before completion, fix Docker networking first and rebuild.

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Funding

This work has received funding from the PIONERA project (Enhancing interoperability in data spaces through artificial intelligence), a project funded in the context of the call for Technological Products and Services for Data Spaces of the Ministry for Digital Transformation and Public Administration within the framework of the PRTR funded by the European Union (NextGenerationEU)

License

Ontology Hub is available under the Apache License 2.0.