SPARQL and relational databases: getting started

Asking about tables and columns and doing a simple join.

In an earlier project I did querying relational data with SPARQL, I wanted to demonstrate how adding OWL metadata made it possible to answer useful queries that couldn’t have been answered with just the original data. I did this using two simple databases of one table each, but recently, while helping someone who was also using the D2RQ interface to provide access to some relational data, I decided to get more comfortable with using SPARQL to query data from multi-table relational…