Translate Sparql to SQL without database connection

[Prateem Mandal]

Hi,

I want to use OnTop as a SQL generator without connecting to any database. Is this possible? If so how? For ex. I was not able to figure out how to provide target SQL engine.

I found this thread https://groups.google.com/g/ontop4obda/c/Op_G3bmRJo8/m/1935Sf1zAQAJ where it is mentioned that this is not possible and that a connection to database is needed to extract the metadata. I would be happy to provide the metadata as a object (or serialized file).

If in order to do this I would need to modify OnTop, can you please outline how to achieve this?

Thanks
Prateem

[Benjamin Cogrel]

Hi Prateem,

Sorry for the late reply.

Yes, there is a way to avoid having Ontop connecting to the data source. First, you can pass the DB metadata as a JSON document. If this metadata is sufficient (all the SQL queries are parsed by Ontop and the metadata is complete), Ontop won't fetch metadata from the data source directly. 

At runtime, you can just ask the system to reformulate the query for you, like for instance in https://github.com/ontop/ontop/pull/577 .

Please enable ontop.reformulateToFullNativeQuery. That way the SQL query will use the same variables as the SPARQL one.

Note that we may refactor this reformulation mechanism in the future and deprecate this configuration entry.

For the JDBC URL, you can create a fake one. Just make sure to URLs of the correct SQL dialect, as this information is used by Ontop for recognizing the dialect.

Best,

Benjamin

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[Prateem Mandal]

Thanks Benjamin. I see your solution is more compact than what I ended up using (which I copied from one of the test cases).



The exact code is here. 

I will try out your suggested approach and report back if I face issues.

Thanks
Prateem

PS:
I had considerable difficulty in resolving library conflicts with the rest of the poc application and ensuring a reproducible build but was able to muddle my way through it.