Apache Marmotta Delete All Graphs using SPARQL Update

Question

I am trying to clear all loaded graphs into my Apache Marmotta instance. I have tried several SPARQL queries to do so, but I am not able to remove the RDF/XML graph that I imported. What is the appropriate syntax to do so?

Answer 1

Try this query:

DELETE WHERE { ?x ?y ?z }

Be careful, as it deletes every triple in the database, including the built-in ones of Marmotta.

A couple of things I did for experimenting:

1. I downloaded the source code of Marmotta and used the Silver Searcher tool for searching for DELETE queries with the following command:

   ag '"DELETE '
   

   This did not help much.

2. I navigated to the Marmotta installation directory and watched the debug log:

   tail -f marmotta-home/log/marmotta-main.log
   

   This showed that the parser is not able to process the query DELETE DATA { ?s ?p ?o }. The exception behind the "error while executing update" was:

   org.openrdf.sail.SailException: org.openrdf.rio.RDFParseException: Expected an RDF value here, found '?' [line 8]
   [followed by a long stacktrace]
   

   This shows that the parser does not allow variables in the query after DELETE DATA.

3. Based on a related StackOverflow answer, I tried CLEAR / CLEAR GRAPH / DROP / DROP GRAPH, but they did not work.

4. I tried many combinations of DELETE, *, ?s ?p ?p and accidentally managed to get it working with the DELETE WHERE construct. According to the W3C documentation:

   The DELETE WHERE operation is a shortcut form for the DELETE/INSERT operation where bindings matched by the WHERE clause are used to define the triples in a graph that will be deleted.