live/examples/tree2graph.etl

// Transform the top-level tree
// to a graph
rule Tree2Graph
	transform s : Source!Tree
	to t : Target!Graph {

	// Only applies to top-level trees
	guard: not s.parent.isDefined()

	t.name = s.label;
}

// Transform all other trees 
// to a node and an edge that
// connects it to the node
// produced by its parent
rule Tree2NodeAndEdge
	transform s : Source!Tree
	to n : Target!Node {

	// Only applies to trees that
	// have a parent tree
	guard: s.parent.isDefined()

	// Copy the label across
	n.name = s.label;

	// Get hold of the one graph
	// created in the previous rule
	var graph = Target!Graph.all.first();
	graph.nodes.add(n);

	// If the depth of the tree is > 1
	// also create an edge 
	if (s.parent.parent.isDefined()) {
		var e : new Target!Edge;
		e.source ::= s.parent;
		e.target = n;
		graph.edges.add(e);
	}
}