The KGraph is the basic data structure used by the KIELER Infrastructure for Meta-Layout to describe and work with graphs. While developing layout algorithms, it is often necessary to assemble very specific graphs to see what the algorithm does with them. This is what the KGraph Text language was designed for: to be a simple language to assemble KGraphs for testing purposes.
This short tutorial will first introduce you to the KGraph and then walk you through writing your first KGT file. Grab a cup of tea and a few biscuits and work your way through it.
Before starting the tutorial, make sure that you have either an Eclipse installation with the KIELER KGraph Editing and Visualization feature installed from our update site or our Standalone KGraph Editor. |
Start by adding a few nodes. Enter the following text into the editor:
knode node1 |
The KLighD view should update itself and show a rectangle that represents the node. Add two other nodes, node2
and node3
, to the graph.
Let's add connection points to the nodes. Add two ports to node1
by adding the following text under the size specification of the node:
kport port1_1 { size: width=10 height=10 } kport port1_2 { size: width=10 height=10 } |
One of the nodes in the KLighD view should now have black ports in the top left corner. This is of course not where we want the ports to end up, so we will have to tell the layout algorithm to place them wherever it's most convenient. The corresponding layout option is called port constraints. Add the following two lines under the size specification of node1
to set the proper constraints on it:
properties: de.cau.cs.kieler.portConstraints=FREE |
The KGT editor has auto completion that you can trigger by pressing Ctrl+Space. The list that pops up shows you everything that can be added at the current cursor position. This is especially handy when it comes to property IDs and possible property values. |
The KLighD view should be updated again and place all ports on the left side of their node. Add two ports, port2_1
and port2_2
, to node2
. Also, add a port port3_1
to node3
.
It's now time to connect the nodes. Add two edges to the graph that originate at node1
by adding the following lines under the port definitions of node1
:
kedge (:port1_2 -> node2:port2_1) kedge (:port1_1 -> node3:port3_1) |
Edges can start and end at a node or at a port. The source node does not need to be explicitly specified since it is clear from the context (the edges are defined in the body of the source node, after all). The target needs the node to be specified, with an optional target port. Add another edge that starts at port2_2
and ends at port3_1
. By now, the KLighD view should show something like this:
One of the problems here is that it is not immediately clear from the drawing which rectangle belongs to which node. This can easily be remedied by adding labels. Start by adding a label to the first node:
klabel "Node 1" |
In the same way, add labels to the other nodes. You will notice that the placement of the labels is not very good. Add the following line to the properties
section of each node:
de.cau.cs.kieler.nodeLabelPlacement="INSIDE H_LEFT V_TOP" |
This will place the labels at the top left corner inside each node. Of course, there are other possible placements you can experiment with. Note that while the value of the port constraints option above could be simply written as FREE
, the value of this option needs to be put in quotation marks. This is because this option's value is actually a set of values.
Labels can also be added to ports and are then properly placed by the layout algorithm as well... |
Let's add a final touch to the graph. Currently, the edges are routed as polylines with slanted edge segments. If we want to change that, we need to tell the layout algorithm to use another edge routing algorithm. Add a new properties
section to the beginning of the file:
properties: de.cau.cs.kieler.edgeRouting=ORTHOGONAL |
Your result could look something like this:
So much for a first glance at how KGT editing works. The rest of this page is devoted to a more detailed explanation of the syntax of the format.