GraphML

Standard GraphML with typed <key> declarations and <data> values. Best-supported format for interop — most graph tools export it natively.

Minimum viable example

graph.graphml

<?xml version="1.0" encoding="UTF-8"?>
<graphml xmlns="http://graphml.graphdrawing.org/xmlns">
  <key id="lbl" for="node" attr.name="label" attr.type="string"/>
  <key id="age" for="node" attr.name="age"   attr.type="int"/>
  <key id="w"   for="edge" attr.name="weight" attr.type="double"/>
  <graph edgedefault="directed">
    <node id="n1">
      <data key="lbl">Alice</data>
      <data key="age">34</data>
    </node>
    <node id="n2"><data key="lbl">Bob</data></node>
    <edge source="n1" target="n2"><data key="w">0.8</data></edge>
  </graph>
</graphml>

Download example

Supported attribute types

attr.type	Maps to	Note
int, long, float, double	number	Range/precision not checked — all become JS numbers.
boolean	boolean	"true" / "false" (case-insensitive) and "1" / "0".
string	string	Promoted to date if every value is ISO 8601 (see below).

GraphML’s schema has no list type that Knotviz reads — represent arrays as pipe-delimited strings inside an attr.type="string" column and Knotviz will NOT auto-detect them (unlike CSV pair). If you need real arrays, the safer path is GEXF’s liststring or JSON.

Dates in GraphML

GraphML has no native date type, so the convention is: declare the column as attr.type="string" and store ISO-8601 values.

<key id="joined" for="node" attr.name="joined" attr.type="string"/>
...
<data key="joined">2021-03-15</data>
<data key="joined">2021-03-15T12:00:00Z</data>

Knotviz re-inspects the column after parse. If every value matches ISO 8601, it re-classifies to date, and you get a date picker in filters + a timeline gradient in Analyze. If even one value isn’t ISO, it stays string.

Opting out. If you have an ISO-looking value that isn’t actually a date — a version tag like 2021-03-15, say — stop it from matching the regex. Prefix with v, drop the dashes, or wrap it: v2021-03-15, 20210315, or ver:2021-03-15 all stay as string.

Structural mappings

GraphML element	Becomes	Note
<node id="…">	NodeInput.id	Required.
Node <key attr.name="label">	NodeInput.label	Display text.
Node <key attr.name="x">, <key attr.name="y">	NodeInput.x / .y	Numeric. Positions rules apply.
Any other node <data>	Node property	Typed per the <key> declaration.
Edge <key attr.name="weight">	EdgeInput.weight	Numeric. Drives edge filtering + size.
Any other edge <data>	Dropped	Knotviz edges only carry weight.

<default> inside a <key> is honoured when a node omits that <data> element.

Coming from another tool

NetworkX

nx_to_graphml.py

import networkx as nx
nx.write_graphml(G, "graph.graphml")

Gephi

File → Export → Graph File → .graphml. Uncheck “Normalize values” to keep original attribute precision. Positions are preserved if you’ve run a layout.

yEd

File → Export → GraphML (.graphml). yEd adds visual styling (<y:Geometry>, <y:Fill>) — Knotviz ignores it cleanly. Structure loads; appearance does not transfer.

Cytoscape

File → Export → Network to File → GraphML. The node id will be Cytoscape’s internal id, not the display name — make sure a name attribute is also present. If you rename name → label, Knotviz picks it up as the display label automatically.

igraph (R)

igraph_to_graphml.R

library(igraph)
write_graph(g, "graph.graphml", format = "graphml")

Gotchas

• Edges can’t carry arbitrary data. Only weight transfers. Any other <data> on edges is dropped on load.
• No array type. Pipe-delimited strings stay as strings — no auto-detection. Use JSON or GEXF (liststring) if you need real arrays.
• yEd visual styling is ignored. <y:Geometry>, <y:Fill>, etc. parse cleanly but don’t render.
• Hyperedges are not supported. A <hyperedge> element will parse but no edge is created.
• Multiple <graph> elements — only the first is read. A warning is logged if more exist.
• Silent skips land in the console. Nodes without a valid id, <data> with an unknown key, edges referencing unknown nodes — all are dropped with a console.warn. Open devtools if a count looks off.
• No streaming parser. Files above ~500k nodes may OOM a 4 GB browser tab — see limits for the hard ceiling.
• UTF-8 recommended. Knotviz doesn’t strip a leading BOM before handing the document to the XML parser. If you hit a “Malformed GraphML XML” error on a file that looks fine, check the first bytes and save without BOM.