15.1.5 XML File Formats

Graph ML

The graph server (PGX) supports loading graphs from files using the XML-based Graph ML format. Graphs already in memory may also be exported into GraphML files. See GraphML specification for a detailed description of the XML schema.

PGX GraphML Limitation

PGX does not support all features of the GraphML format. Some of the limitations are:

• If the graph is undirected (edgedefault="undirected"), then edge properties are not supported
• All vertices (edges) must have the same amount and type of vertex (edge) properties
• port, default, and hyperedge are not supported

Example 15-6

The following example graph consists of 3 vertices and 3 edges. Each vertex has an integer property named number and each edge has a string property named label. Note that the edges are directed and that the strings for the property do not have to be put in (double) quotation marks.

<?xml version="1.0" encoding="UTF-8"?>
<graphml xmlns="http://graphml.graphdrawing.org/xmlns">
    <key attr.name="number" attr.type="integer" for="node" id="number"/>
    <key attr.name="label" attr.type="string" for="edge" id="label"/>
    <graph edgedefault="directed">
        <node id="1">
            <data key="number">2</data>
        </node>
        <node id="2">
            <data key="number">45</data>
        </node>
        <node id="3">
            <data key="number">83</data>
        </node>
        <edge target="2" source="1">
            <data key="label">this graph</data>
        </edge>
        <edge source="3" target="2">
            <data key="label">forms a</data>
        </edge>
        <edge target="1" source="3">
            <data key="label">triangle</data>
        </edge>
    </graph>
</graphml>

Caution:

Due to the verbose nature of XML, the GraphML format comes with a large overhead compared to other file-based graph formats. You must use a different format if you want to consider the load or store performance and file size as important factors.