rdf2graphml

Python library for easy converting any RDF to other formats, like GraphML compatible with yEd or drawio.

The RDF-to-GraphML conversion is very customizable. The basic idea is to extend an existing model or ontology with visualization properties. The ontology for these annotation properties is found here: rdf2graphml.ttl.

If you do not have a model or ontology you can specify a JSON configuration file.

Usage

[-h] [-V] [-v] [--base_dir BASE_DIR] [--type_as_edge] [-m MODEL] [-c CONFIG] -o OUTPUT [inputs ...]

If you use -m and -c option, the JSON configuration will be loaded first. The model properties will then overwrite the JSON configuration. In any case the command line option --type_as_edge takes precedence.

The converter automatically detects the format of your inputs files based on their file extensions. The following formats are supported out of the box:

Standard RDF Formats: Any format supported by rdflib and explicit support for .jsonld.

Graffl: Native support for parsing .graffl files - see the graffl project.

Configuration

While the annotation properties in the provided RDF ontology use camelCase (e.g. rdf2graphml:lineWidth), the corresponding keys in the JSON configuration use snake_case (e.g. line_width). Your actual RDF URIs used in the configuration remain unchanged.

Annotating a Model or Ontology

Annotating a model or ontology is simple, just add the layout properties to your types:

@prefix rdf2graphml: <https://www.hedenus.de/rdf2graphml/> .

<http://example.org#System> a owl:Class ;
  rdf2graphml:icon "icons/my_icon.png" .

<http://example.org#note> a rdf:Property ;
  rdf2graphml:color "#FFAAAA" ;
  rdf2graphml:lineWidth "2.0" .

Example JSON Configuration

{
  "namespaces": {
    "ex": "http://example.org/ontology/",
    "schema": "http://schema.org/",
    "rdf2": "https://www.hedenus.de/rdf2graphml/"
  },
  "icon_height": 80,
  "preferred_language": "de",
  "type_as_edge": false,
  "node_properties": [
    "http://www.w3.org/2000/01/rdf-schema#comment",
    "http://example.org/ontology/internalId"
  ],
  "icon_locators": [
    "http://example.org/ontology/hasIcon",
    "https://www.hedenus.de/rdf2graphml/icon"
  ],
  "group_type": "http://example.org/ontology/SystemBoundary",
  "group_contains": "http://example.org/ontology/containsComponent",
  "default_node_style": {
    "blank_nodes": {
      "color": "#F0F0F0",
      "shape": "ellipse"
    },
    "uri_nodes": {
      "color": "#DAE8FC",
      "shape": "roundrectangle"
    }
  },
  "type_styles": {
    "http://example.org/ontology/Database": {
      "icon": "database_icon.png",
      "color": "#FFE6CC",
      "shape": "cylinder",
      "priority": 20
    },
    "http://example.org/ontology/Service": {
      "color": "#D5E8D4",
      "shape": "rectangle",
      "priority": 10
    },
    "https://www.hedenus.de/rdf2graphml/List": {
      "color": "#FFFF88",
      "shape": "hexagon",
      "priority": 100
    }
  },
  "edge_styles": {
    "http://example.org/ontology/calls": {
      "color": "#0000FF",
      "line_type": "line",
      "line_width": "2.0",
      "target_arrow": "standard",
      "label": "ruft auf"
    },
    "http://www.w3.org/1999/02/22-rdf-syntax-ns#type": {
      "color": "#888888",
      "line_type": "dashed",
      "target_arrow": "transparent_circle"
    }
  },
  "include_predicates": [
    "http://example.org/*",
    "http://www.w3.org/1999/02/22-rdf-syntax-ns#type"
  ],
  "exclude_predicates": [
    "http://example.org/ontology/ignoredProperty"
  ],
  "include_types": [
    "*"
  ],
  "exclude_types": [
    "http://example.org/ontology/HiddenType"
  ]
}

Reference

General Settings

• namespaces (object): A dictionary mapping prefixes to namespace URIs. These custom namespaces are registered with the converter to generate shorter QName labels (e.g., ex:Node) for nodes and edges instead of full URIs. Overrides existing prefixes in the source graph.
• icon_height (integer): The target height in pixels for downloaded/loaded icons. The width is scaled proportionally using Lanczos resampling. Default: 64.
• preferred_language (string): The language tag used to pick the primary rdfs:label for display purposes (e.g., "en" or "de"). If not found, it falls back to a label without a language tag, or an arbitrary one. Default: "en".
• type_as_edge (boolean): If true, rdf:type relations are drawn as explicit edges in the graph. If false, they are collected as node attributes (GraphML Data). Default: false.

RDF Mapping & Extraction

• node_properties (list of strings): A list of URIs. Triples with these predicates are explicitly prevented from becoming edges. Instead, their objects are attached to the subject node as GraphML data attributes.
• icon_locators (list of strings): A list of URIs. If a node has one of these predicates, the converter interprets the object as a URL or local file path to an image, downloads and embeds it.

Groups & Hierarchies (Nested Graphs)

• group_type (string): The URI of the rdf:type that identifies a node as a group container.
• group_contains (string): The URI of the predicate used to link a group node to its children. These triples establish the nested graph hierarchy and will not be drawn as visible edges.

Styling

• default_node_style (object): Fallback styling for nodes.

  • blank_nodes: Style object (color, shape) applied to RDF Blank Nodes. Default: Grey ellipse.
  • uri_nodes: Style object (color, shape) applied to standard URI nodes. Default: Light-blue roundrectangle.

• type_styles (object): Maps rdf:type URIs to specific styles.

  • icon (string): URL or local path to a default image/icon for this type. Takes precedence over shape. If the image fails to load, the converter gracefully falls back to the configured shape.
  • color (string): Hex color code (e.g. "#ADD8E6").
  • shape (string): Shape identifier
  • priority (integer): If a node has multiple types, the style with the highest priority wins.

• edge_styles (object): Maps predicate URIs to edge styles.

  • color (string): Hex color code (e.g. "#ADD8E6").
  • line_type (string): Line type identifier.
  • line_width (string): Line width (e.g. 2.0).
  • target_arrow (string): Arrow types identifier.

RDF Lists

The converter automatically aggregates rdf:first/rdf:rest lists into a single node. You can style this generated node by targeting the URI https://www.hedenus.de/rdf2graphml/List.

  "type_styles": {
      "https://www.hedenus.de/rdf2graphml/List": {
          "color": "#FFD700",
          "shape": "hexagon",
          "priority": 100
    }}

Links

If you want to create clickable hyperlink you can use the type rdf2graphml:Link. If a node is hyperlink then the label text will be underlined. If the node is a blank node, then the url property is taken from rdf:value.

Filtering

Filters accept Unix shell-style wildcards (e.g., * or http://example.org/*). The exclusion rules are always evaluated before the inclusion rules.

• include_predicates (list of strings): Only predicates matching these patterns will be drawn as edges. If empty, all predicates (that are not structural/excluded) are allowed.
• exclude_predicates (list of strings): Predicates matching these patterns are completely ignored.
• include_types (list of strings): Only nodes possessing an rdf:type matching these patterns are drawn.
• exclude_types (list of strings): Nodes possessing an rdf:type matching these patterns are explicitly ignored.

Styles known by yEd

Also see the application's documentation.

shape:

• diamond
• ellipse
• fatarrow (pointing to right)
• fatarrow2 (pointing to left)
• hexagon
• octagon
• parallelogram (skewed right)
• parallelogram2 (skewed left)
• rectangle3d
• rectangle
• roundrectangle
• star5
• star6
• star8
• trapezoid (pointing up)
• trapezoid2 (pointing down)
• triangle (pointing up)
• triangle2 (pointing down)

line_type:

• dashed
• dashed_dotted
• dotted
• line

target_arrow:

• circle
• delta
• diamond
• none
• plain
• short
• standard
• transparent_circle
• white_circle
• white_delta
• white_diamond

Credits

• User icon (alice.png) created by Heykiyou - Flaticon
• Battery icon (battery.png) created by Freepik - Flaticon
• User icon (user.png) created by meaicon - Flaticon