Re: [d2rq-dev] RDF files to TTL

[Richard C. <ri...@cy...>]

Hi Alexander,

On 2 Oct 2013, at 10:09, Александр Алексиянц wrote:
> I'd like to use D2RQ for querying databases that is represented with RDF.

That's not what D2RQ is for. You have the wrong software.

D2RQ can:

- Export the data in relational databases (like MySQL or PostgreSQL) to RDF formats (like .nt, .rdf, .ttl)
- Query the data in relational databases with the SPARQL

If you want to query RDF data (like .nt, .rdf, .ttl) then you need an RDF database, also known as an RDF store or triple store.

I recommend Apache Fuseki for smaller RDF datasets (up to a few million triples), and OpenLink Virtuoso for larger datasets.

If the file is small enough, then you can also directly query it with command-line tools without first loading it into an RDF store, as described here:
http://richard.cyganiak.de/blog/wp-content/uploads/2013/09/jena-sparql-cli-v1.pdf

> I have a database that is stored in N3 file. I want to query this database by D2RQ. As far as I understand I can query only data bases in mapping file (in .ttl files).

The purpose of a mapping file is to describe the relationships between database tables/columns and RDF classes/properties. The mapping file does *not* contain the data to be queried.

> So, I need to generate a .ttl file from .n3.

.n3 is simply an older version of .ttl, with some extra features that are rarely used. Often, you can simply rename a .n3 file to .ttl and it will work with modern software that can read .ttl.

But see above -- D2RQ cannot query RDF files.

Best,
Richard


> But I only found a way to generate a .ttl from already existing data base by using some DBMS software like MySQL, PostgreSQL, etc. Is there a way to do that?
> 
> With regards.
> Alexander Aleksiyants
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