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I've been trying to figure out how to mount a SPARQL endpoint for a couple of days, but as much as I read I can not understand it.

Comment my intention: I have an open data server mounted on CKAN and my goal is to be able to use SPARQL queries on the data. I know I could not do it directly on the datasets themselves, and I would have to define my own OWL and convert the data I want to use from CSV format (which is the format they are currently in) to RDF triple format (to be used as linked data).

The idea was to first test with the metadata of the repositories that can be generated automatically with the extension ckanext-dcat, but is that I really do not find where to start. I've searched for information on how to install a Virtuoso server for the SPARQL, but the information I've found leaves a lot to be desired, not to say that I can find nowhere to explain how I could actually introduce my own OWLs and RDFs into Virtuoso itself.

Someone who can lend me a hand to know how to start? Thank you

germaaan
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  • 1. You'd need an RDB2RDF mapping, i.e. you have to map tables/columns to classes/properties etc. in the ontology that you have to create first. Then you can use a tool like Ontop to convert the data or use an R2RML mapping that converts SPARQL queries to SQL queries, i.e. you wouldn't have to convert the data first. Yet, you have to write the R2RML mapping – UninformedUser May 21 '17 at 12:24

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I'm a little confused. Maybe this is two or more questions?

1. How to convert tabular data, like CSV, into the RDF semantic format?

This can be done with an R2RML approach. Karma is a great GUI for that purpose. Like you say, a conversion like that can really be improved with an underlying OWL ontology. But it can be done without creating a custom ontology, too.

I have elaborated on this in the answer to another question.

2. Now that I have some RDF formatted data, how can I expose it with a SPARQL endpoint?

Virtuoso is a reasonable choice. There are multiple ways to deploy it and multiple ways to load the data, and therefore LOTs of tutorial on the subject. Here's one good one, from DBpedia.

If you'd like a simpler path to starting an RDF triplestore with a SPARQL endpoint, Stardog and Blazegraph are available as JARs, and RDF4J can easily be deployed within a container like Tomcat.

All provide web-based graphical interfaces for loading data and running queries, in addition to SPARQL REST endpoints. At least Stardog also provides command-line tools for bulk loading.

Mark Miller
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