SimpleGraph-MapSystem

SimpleGraphModule

SimpleGraph MapSystem module

The SimpleGraph MapSystem module supplies a simple wrapper for a graph with nodes that have key/value pairs in form of HashMaps. We would not really need this since Apache Tinkerpop/Gremlin already supplies us with properties per node/vertex. Still this system is useful as a helper system and to illustrate the wrapping concepts and possibilities of SimpleGraph see java.api.Map.

Sources

• System: MapSystem.java
• JUnit-Test: TestMapSystem.java

Example

Goal

We'd like to create a tree of carbrands with corresponding car makes.

CarGraph

The nodes of this graph are clickable and will lead you to the wikidata pages of the carmakes and carbrands.

Explanation

The following JUnit Test source code is commented with the explanation on how the MapSystem works.

  @Test
  public void testMapSystem() throws Exception {
    // create a map system and connect to init
    MapSystem ms=new MapSystem();
    ms.connect();
    // init some maps of carbrands and cars each map shall later represent a
    // vertex in the graph with it's properties
    Map[] carbrandmaps= {
        initMap("name","Ferrari","country","Italy","wikidataid","Q27586"),
        initMap("name","Porsche","country","Germany","wikidataid","Q40993"),
        initMap("name","Ford","country","United States","wikidataid","Q44294")
    };
    Map[] carmakemaps= {
        initMap("name","308","year",1984,"wikidataid","Q1407659","brand","Ferrari"),
        initMap("name","328","year",1989,"wikidataid","Q1407669","brand","Ferrari"),
        initMap("name","901","year",1964,"wikidataid","Q2104537","brand","Porsche"),
        initMap("name","2017 GT","year",2017,"wikidataid","Q23856323","brand","Ford")
    };
    // create MapNodes with the given kind "carbrand" or "car" based on the maps
    MapNode startNode=null;
    for (Map map:carbrandmaps) {
      startNode=new MapNode(ms,"carbrand",map);
    }
    for (Map map:carmakemaps) {
      MapNode mapNode=new MapNode(ms,"car",map);
      // link the node of this car to it's carbrand node using the Gremlin graph traversal
      // language - this is the key action for this example
      ms.g().V().hasLabel("carbrand").has("name",map.get("brand")).forEachRemaining(brandNode->{
        brandNode.addEdge("brand", mapNode.getVertex());
      });
    }
    // set a start node for the system
    // any node will do and for this example it is not really necessary - each node
    // has the full graph accesible
    ms.setStartNode(startNode);
    // uncomment if you'd like to see all the node details
    // debug=true;
    if (debug)
      ms.g().V().forEachRemaining(SimpleNode.printDebug);
    // generate a graphviz graph based on this start node
    // show the "brand" edges
    // show the "name" for each node
    // use wikidataid as the identifier
    // and extend to a full url using the WIKIDATA_URL_PREFIX
    // use the rankDir RL = right left
    // and name the graph "CarGraph"
    String graphViz = TestRythm.generateGraphViz(ms.getStartNode(), "brand", "name", "wikidataid",
        WIKIDATA_URL_PREFIX,"RL","CarGraph");
    // uncomment if you'd like to see the graph source code
    // the rendered graph is available at http://www.bitplan.com/index.php?title=SimpleGraph#CarGraph
    // debug = true;
    if (debug)
      System.out.println(graphViz.trim());
    // check that the graph contains one of the expected graphviz code lines
    assertTrue(graphViz.contains("\"Q27586\" [ label=\"Ferrari\" URL=\"https://www.wikidata.org/wiki/Q27586\"]"));
  }