Find Public and Alive SPARQL Endpoints
Wikidata stores data about a variety of subjects and provides a SPARQL endpoint for easy access to this data. In particular, it lists the addresses of other SPARQL endpoints.
This example queries the Wikidata SPARQL endpoint to find other SPARQL endpoints. Then it sends each of them a (trivial) example query, waits at most a few seconds and finally checks whether the result (if any) is as expected.
Ask Wikidata about known SPARQL endpoints.
The total number of endpoints.
Get the labels.
Specify a trivial example query: A SPARQLSelect with an empty graph pattern.
What to expect as result? A single solution without any variable bindings.
You can verify this by applying the example query to sample RDFStore objects (an empty one in this case).
Query each SPARQL endpoint with the example query. If there is no response after a few seconds, then time out. If there is an unexpected result, then count it as a failure.
Number of successes, timeouts and failures.
Make a pie chart.