code: private void initializeIfNeeded() throws BackendInitializationException,
              BackendNewInstanceException {
          if (isClosed()) {
              throw new IllegalStateException("Knowledge source already closed!");
          }
          if (this.inDataSourceGetter == null) {
              this.inDataSourceGetter
                      = new SubtreePropositionDefinitionGetterRegular(this, true);
          }
          if (this.collectSubtreeGetter == null) {
              this.collectSubtreeGetter
                      = new SubtreePropositionDefinitionGetterRegular(this, false);
          }
      }
docs: Connect to the knowledge source backend(s).