code: @Override
      public Boolean call() {
  
          // If the model has not been uploaded fetch it and upload the graph
          if (!this.graphStoreManager.containsGraph(this.modelUri)) {
              Model model = fetchModel(this.modelUri, this.syntax);
              if (model == null || model.isEmpty()) {
                  return Boolean.FALSE;
              }
              this.graphStoreManager.putGraph(this.modelUri, model);
          }
  
          return Boolean.TRUE;
      }
docs: Given the model uri, this method takes care of retrieving the remote model and any imported documents
  and uploads them all to the graph store within the same graph. This implementation relies on Jena's embedded
  support for retrieving ontologies and their imports.
  
  ATTENTION: When deleting models (in cases where several models import a common model) we may remove the
  first ontology uploaded, with it the imported model will also be deleted and as a result any other model
  that imported the common one will not have it available any more.
  TODO: To be fixed
  
  @return True if the model was fetched or is already uploaded. False if it could not be obtained