The Bio-jETI Framework - User-Level Workflow Design: A Bioinformatics Perspective - page 33

and running threads, and is thus useful for experimenting, testing and
debugging.
Fig. 2.3 Workflow execution via the Tracer plugin
Figure 2.3 shows the jABC user interface during the execution of a
workflow model with the Tracer: The plugin provides a small “control
panel” (left), which can be used, for instance, to start the complete exe-
cution of the workflow, to steer its step-by-step execution, or to stop at
breakpoints. Moreover, it provides basic monitoring facilities, such as an
execution history (as shown in the figure) and an overview of the running
threads, the objects in the execution context and events (not visible in
this figure). The current state of the execution is in addition visualized
in the workflow model: the currently executed SIB is marked by a small
green overlay icon, and the four recently followed branches are colored
green. In the figure, workflow execution has passed the SIBs that execute
the image processing steps for creation of custom birthday cards as de-
scribed in Section 1.1.1, and the result is now available and ready to be
sent.
In order to use the Tracer for executing an SLG, all its SIBs have to
implement the Tracer interface. This requires the corresponding SIB to
provide an execute() method that contains the code that is to be called
during execution, possibly making use of the parameters of the SIB. This
code can be provided completely in the SIB, but also use libraries, or call
remote services. Furthermore, this method has to define a return value
that has to be one of the labels for outgoing branches and represents
the result of the method invocation, that is, for instance, whether it was