code: @Override
      public Set<URI> listStoredGraphs() {
  
          StringBuilder strBuilder = new StringBuilder()
                  .append("SELECT DISTINCT ?graph WHERE {").append("\n")
                  .append("GRAPH ?graph {").append("?s ?p ?o").append(" }").append("\n")
                  .append("}").append("\n");
  
          return listResourcesByQuery(strBuilder.toString(), "graph");
      }
docs: Figure out the models that are already in the Knowledge Base
  
  @return the Set of URIs of the models loaded