Support for subgraph / hierarchy

[songhn233]

Many graph formats support hierarchical graph so can nest graphs under the top graph. This means that three elements may be needed: edges, nodes, and subgraphs

Can JGF handle this case?

[wshayes]

Not at the moment. We have discussed handling it, but I don't remember the final state of those conversations (all discussions are in the issues).

[songhn233]

Not at the moment. We have discussed handling it, but I don't remember the final state of those conversations (all discussions are in the issues).

I found these discussions in #22.

But I have come to the conclusion that this structure can now only be supported by additional custom properties.

Existing structures can certainly be represented by metadata or additional properties, but this will lead to a confusing representation of the nest graph, which runs counter to the purpose of the specification.

Currently there seems to be only one subformat bel-jsongraph-format, we can design a nested-graph-format to standardize this representation without burdening existing specification.