Hypergraph JSON de/serialisation

[toumix]

DisCoPy already has JSON de/serialisation for the Diagram class, see dumps and loads.

We need the same feature for the Hypergraph class.

[colltoaction]

For example, AlgebraicJulia has several schemas that @epatters worked on here:

https://github.com/AlgebraicJulia/Catlab.jl/blob/main/src/wiring_diagrams/JSON.jl

Given the maturity of the Julia ecosystem I think this can be a great implementation advantage.

[toumix]

Yes it would be nice to use the same convention as in Catlab!

One caveat though is that the schema you refer to only deals with monogamous hypergraphs (see issue #25), i.e. every wire has exactly two ports as endpoints whereas the hypergraphs in DisCoPy have spiders which can connect to an arbitrary number of ports.

[colltoaction]

What is the goal of this issue? Is it interoperability? Because just to get a JSON file an option is to take the DiGraph and export using NetworkX:

• https://networkx.org/documentation/stable/reference/readwrite/json_graph.html

discopy/discopy/hypergraph.py

Lines 1094 to 1098 in ec3c570

	def to_graph(self) -> Graph:
	"""
	Translate a hypergraph into a labeled graph with nodes for inputs,
	outputs, boxes, domain, codomain and spiders.
	"""

[toumix]

The goal of this issue is de/serialisation so that a Hypergraph can e.g. be stored on the disk, sent over the network and loaded somewhere else by another DisCoPy script. Interoperability would come as a second step, but for now there is no established format to serialise hypergraph representations of string diagrams.

This could be done by composing the existing methods to_ and from_graph with the existing NetworkX serialisation as you suggest, but AFAIK the label of the boxes would be lost in the process.

The easiest way would be to simply extend the to_ and from_tree methods to translate hypergraphs into JSON and back, directly translating the attributes dom, cod, boxes, wires, spider_types.