ontopic-open-data-hub.md

USE CASE Open Data Hub-Virtual Knowledge Graph BY Ontopic

Context

Open Data Hub-Virtual Knowledge Graph (ODH-VKG) is a joint project between NOI Techpark and Ontopic for publishing South Tyrolean tourism data as a Knowledge Graph. Before the project started, the data was accessible through a JSON-based Web API, backed by a PostgreSQL database. We created a VKG over the database and a SPARQL endpoint that is much more flexible and powerful than the old Web API.

Challenges

1. Data and Mapping. For historical reasons, all the database tables are of two columns id and data, where id is a UUID identifying a row and data is a JSON object containing rich information. In order to access the internal content of data, we have created a customized script to sample the data and extract all possible fields from the data column. Then we create a "relational version" of original table. When there is an array nested in data, we need to create a separate table pointing to the parent table using foreign keys.
2. Ontology. The ontology is mostly based on schema.org, but we often need to extend it. E.g., :BeerGarden rdf:type owl:Class ; rdfs:subClassOf schema:BarOrPub .

Resources

• Websites:
  • Endpoint: https://sparql.opendatahub.bz.it/
  • Source code: https://github.com/noi-techpark/odh-vkg
• Data: A snapshot version of the database is available as a Docker Image
• Mappings: https://github.com/noi-techpark/odh-vkg/blob/master/vkg/odh.obda in Ontop Mapping Syntax
• Ontology: https://github.com/noi-techpark/odh-vkg/blob/master/vkg/odh.ttl
• Tools
  • Ontop for setting up the SPARQL endpoint
  • Ontop Protege plugin for developing ontology and mapping
  • Customized Script for sampling the data and create the "relational version" of the original data.
• Output
  • SPARQL Endpoint