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Fig. 8.2 Graphical user interface of the Editor

To select a codelet, the Editor needs to be connected to the Resource Service.
A predefined set of codelets is provided with the Editor. These include a codelet
for executing shell commands and a codelet for evaluating XQuery expressions. In
addition, workflow designers can plug their own codelets into the YAWL environ-
ment. Similarly, to assign an external application to an atomic task, the application
needs to be exposed as a Web Service and the latter be registered with the YAWL
environment. The YAWL System provides a number of custom services already (cf.
Chap. 7). To associate a Custom Service with a task, the Editor needs to be con-
nected to the Engine. If the Engine is active but the status icon in the Editor (see
bottom left of Fig. 8.2) states it as offline, a connection can be manually established
by invoking the dialogue Engine Connection Settings via menu entry Tools.
If an atomic task is neither manual nor automated, it is an empty task. An empty
task may be a routing task, which is essentially a silent task that is used only for
routing purposes. Routing tasks are executed internally by the Engine.