'Add a relationship to the source object corresponding to each of the
relationships in *pkg_reader* with its target_part set to the actual
target part in *parts*.'

@staticmethod
def _unmarshal_relationships(pkg_reader, package, parts):

    for (source_uri, srel) in pkg_reader.iter_srels():
        source = (package if (source_uri == u'/') else parts[source_uri])
        target = (srel.target_ref if srel.is_external else parts[srel.target_partname])
        source.load_rel(srel.reltype, target, srel.rId, srel.is_external)
