@danlipsa, sorry for the delay!
What do you do for ImageData? Is that also considered a partitioned dataset?
For now, only the unstructured data can be output as a partitioned dataset given the format of the data. We could imagine rather easily extending this to image data by putting one partition per MPI rank.
What happens when you save a PD collection that does not have a data assembly. How do you come up with the names for the PDs? Based on index?
I would imagine that we would follow whatever convention the vtkPartitionedDataSetCollections have now in other contexts (writers, ParaView menus, etc.). Most likely a name based off the index of the block in the collection indeed.
What is the API to set/get names of nodes in the tree?
someDataObjectTree->GetMetaData(index)->Set(vtkCompositeDataSet::NAME(), name)someDataObjectTree->GetMetaData(index)->Get(vtkCompositeDataSet::NAME())