[Suggestion] Nested workflows

[GeigerJ2]

See discussion: MADICES/MADICES-2025#21

General guiding principles

• Only one representation of how something is done (interoperability format should be clearly well-defined)
• Minimal changes to previous version
• Minimal set of keywords

With this, we stay at 0.1.x and only add a workflow node type. Example of a nested workflow, as defined by two separate JSON files:

{
  "version": "0.1.1",
  "nodes": [
    { "id": 0, "type": "function", "value": "workflow.get_prod_and_div" },
    { "id": 1, "type": "function", "value": "workflow.get_sum" },
    { "id": 2, "type": "function", "value": "workflow.get_square" },
    { "id": 3, "type": "input", "value": 1, "name": "x" },
    { "id": 4, "type": "input", "value": 2, "name": "y" },
    { "id": 5, "type": "output", "name": "result" }
  ],
  "edges": [
    { "target": 0, "targetPort": "x", "source": 3, "sourcePort": null },
    { "target": 0, "targetPort": "y", "source": 4, "sourcePort": null },
    { "target": 1, "targetPort": "x", "source": 0, "sourcePort": "prod" },
    { "target": 1, "targetPort": "y", "source": 0, "sourcePort": "div" },
    { "target": 2, "targetPort": "x", "source": 1, "sourcePort": null },
    { "target": 5, "targetPort": null, "source": 2, "sourcePort": null }
  ]
}

{
  "version": "0.1.1",
  "nodes": [
    { "id": 0, "type": "workflow", "value": "prod_div.json" },
    { "id": 1, "value": 1, "type": "input", "name": "a" },
    { "id": 2, "value": 2, "type": "input", "name": "b" },
    { "id": 3, "type": "output", "name": "final_result" }
  ],
  "edges": [
    { "target": 0, "targetPort": "x", "source": 1, "sourcePort": null },
    { "target": 0, "targetPort": "y", "source": 2, "sourcePort": null },
    { "target": 3, "targetPort": "null", "source": 0, "sourcePort": "result" }
  ]
}

• aiida
• jobflow
• pyiron
• plot function
• Port validation that ports of the outer graph map correctly to the ports of the inner graph