## Details

The following data fields are immutable, and so they can not be removed:

 * `id` : The `id` field is used to uniquely identify an element in the graph.
 * `source` & `target` : These fields define an edge's relationship to nodes, and this relationship can not be changed after creation.
 * `parent` : The `parent` field is a reserved field for the future implementation of compound nodes.
