GML

GML is an interoperability format, not a complete Helios state container. Use it when another graph tool needs GML. Use ZXNet, BXNet, or XNet when a Helios workflow needs full typed attributes and visualization state.

Helios accepts standard GML and a looser dialect with quoted keys and unquoted scalar strings. Export sanitizes unsafe keys, deduplicates collisions, skips values that cannot be represented safely, and exposes serialization warnings.

JavaScript

import HeliosNetwork from "helios-network";

const network = await HeliosNetwork.create({ directed: true });
const nodes = network.addNodes(2);
network.addEdges([[nodes[0], nodes[1]]]);
network.nodeAttribute("label", ["source", "target"]);

await network.saveGML({ path: "./graph.gml" });
const restored = await HeliosNetwork.fromGML("./graph.gml");

Helios Web

await helios.loadNetwork(file, { format: "gml" });

const graphOnly = await helios.savePortableNetwork("gml", {
  output: "blob",
  includeVisualization: false,
});

includeVisualization: true is rejected for GML because GML has no native place for Helios view state.

Python

from helios_network import Network, read_gml

network = Network(directed=True, node_capacity=2, edge_capacity=1)
nodes = network.add_nodes(2)
network.add_edges([(nodes[0], nodes[1])])
network.nodes["label"] = ["source", "target"]

network.save_gml("graph.gml")
restored = read_gml("graph.gml")

Native C

#include <helios/CXNetwork.h>
#include <helios/CXNetworkGML.h>

CXNetworkRef network = CXNewNetworkWithCapacity(CXTrue, 2, 1);
CXNetworkWriteGML(network, "graph.gml");

CXNetworkRef restored = CXNetworkReadGML("graph.gml");
CXFreeNetwork(restored);
CXFreeNetwork(network);

After lossy reads or writes, check CXNetworkSerializationLastWarningMessage() when warnings are important to the workflow.

CLI

helios session start --network ./graph.gml
helios call <sessionId> network.save --json '{"format":"zxnet","outputPath":"./graph.zxnet"}'
helios call <sessionId> network.save --json '{"format":"gml","outputPath":"./roundtrip.gml"}'

GML is graph-only. Use a Helios-native format such as ZXNet when the saved file must keep visualization state.