Graph queries are used to analyse the actual structure (graph), which can be for example a plant structure.

In XL, queries are enclosed in asterixed parentheses (* *).

The elements in a query are given in their expected order, e.g. (* A A B *) searches for a subgraph which consists of a sequence of nodes of the types A A B, connected by successor edges.

To try out how queries work, we first create a simple plant model.

module Bud extends Sphere(0.1).(setShader(GREEN));
 
module Internode(int age, super.length) extends Cylinder(length, 0.1).(setShader(YELLOW));
 
module Leaf(int age, super.length, double width) extends Parallelogram(length, width).(setShader(GREEN)) 
{
    double area;
 
    { setArea(); }
 
    void setArea() {
        area = length*width;
    }
}
 
protected void init()
[
    Axiom ==> Bud;
]
 
public void run()
[
    Bud ==> 
        Internode(1, 1) 
        [RL(60) Leaf(1, 1, 1)] 
        RH(180)
        Bud
    ;
 
    i:Internode ::> { i[age]++; i[length] += 1; }
    l:Leaf ::> { l[age]++; l[length] += 1; l.setArea(); }
]

We create a new method called analyse(). The method will appear as a new button in the RGG toolbar. Inside this method, we first call the run() method for 3 steps. The result is a simple plant made of 3 internodes and 3 leaves.

public void analyse()
{
    for (apply(3)) { run(); }
 
    println("add here a query example");
}

Replace the text inside the println() one by one by the queries below.

• Find all the internodes in the structure:

(* Internode *)

The query will return ids of all the internodes in the plant structure.

Notice, that when you click with a mouse on an internode in the 3D View window, information about the selected internode will be displayed in the Attribute Editor. In the Attribute Editor, you can check the internode id (e.g. Model$Internode [Internode.1756]) and compare it with the one that was printed in the XL Console. Another option is to look at the node ids in the 2D Graph (Panels → 2D → Graph, in the graph window: View → Redraw).

• Find all newly created internode(s), with age == 1:

(* i:Internode, (i[age] == 1) *)

• Find the internode closest to the bud:

(* Bud < RH < Internode *)

< represents a successor edge