Integrated into our Wikibase is a Query Service which serves as a SPARQL endpoint. A SPARQL endpoint is a user interface for conducting queries in the SPARQL Protocol and RDF Query Language. SPARQL queries allow users to query any database that is structured as linked data, meaning that the data has been encoded in a standard compliant with the Resource Description Framework (RDF). Much the same way SQL is used to query relational databases, SPARQL is used to query graph databases.
The Query Service SPARQL endpoint is automatically formatted to accept queries in a Wikibase environment. For more information on using the Wikibase Query Service, this Wikidata SPARQL tutorial and Wikidata Query Service User Manual provide details for how to conduct SPARQL queries in Wikidata, which is built on the same Wikibase software as the DS Catalog. When enabled, SPARQL endpoints can conduct federated searching across LOD repositories by declaring prefixes, so that linked data from one resource can be queried alongside and in tandem with other linked datasets. For an explanation of this type of SPARQL query, The Su Lab at the Scripps Research Institute has a guide on federated queries.
Please note that as we upload more member data into the DS Wikibase, we will be constructing and sharing sample queries you can use to explore the DS Catalog as Linked Open Data (LOD). Continue to check this space for more updates on sample queries.
If you would like to learn more about the basics of constructing SPARQL queries, these tutorials from Cambridge Semantics and Ontotext may be useful. For further details, the W3C has a full SPARQL specification.