[vtkusers] superclass for composite datareader?

[Peter J. Bismuti]

I have a dataset that has a mixture of data types.  The first is something 
resembling multi-block structured grids (a collection of ordered panels 
creating a surface) and the second is hierarchical data (oct-tree).  

If I was to write a datareader in vtk, what would the best choice of a 
superclass be?  

Thanks