@Override
  public void associate(@NotNull Node<?, ?> node, @NotNull Iterable<NodeSource> sources) {
    ReferenceID nodeID = node.getReferenceID();
    for (NodeSource src : sources) {
      myNodeToSourcesMap.appendValue(nodeID, src);
      mySourceToNodesMap.appendValue(src, node);
    }
    // deduce dependencies
    for (BackDependencyIndex index : getIndices()) {
      index.indexNode(node);
    }
  }
@Override
  public void associate(@NotNull Node<?, ?> node, @NotNull Iterable<NodeSource> sources)