case class Road (g: PropertyGraph)
     extends NodeType (g)
{
     addProperty ("name", "S")
     addProperty ("speedLimit", "I")
     addProperty ("lanes", "I")
     key ("name")
} // Road

case class Intersection (g: PropertyGraph, r1: Road, r2: Road)
     extends EdgeType (g, r1, r2)
{
     addProperty ("control", "S")
} // Intersection

object Test extends App
{
    val g = PropertyGraph ("Athens_roads")

    val main = Road (g)
    main("name")       = "main"
    main("speedlimit") = 35
    main("lanes")      = 2

    val oak  = Road (g)
    oak("name")       = "oak"
    oak("speedlimit") = 45
    oak("lanes")      = 1

    val main2oak = Intersection (g, main, oak)
    main2oak ("control") = "stop_sign"

    g.print ()
    g.display ()
} // Test