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certain services and potential deadlocks or livelocks) are detected. Due to
incorporating aspects that are more specific for the application domain and
the specific workflows, the constraints used within Bio-jETI provide useful
information for the workflow design process, other than the generic properties
described in [75].
Means for runtime validation, a.k.a. debugging functionality, are offered
by most systems via the workflow interpretation facilities (see below) that
provide stack traces or other error messages when execution errors occur. In
Bio-jETI, workflow debugging functionality is provided by the Tracer plugin.
Workflow Execution (Requirement 6)
At least basic workflow execution facilities are provided by all considered sys-
tems. Several systems also support the deployment of the workflow model
into specific (grid) execution language. More general model compilation func-
tionality is basically only available in the domain-independent systems.
In Bio-jETI, workflow execution by interpretation as well as workflow de-
bugging functionality is provided by the Tracer plugin. Comprehensive work-
flow compilation and deployment support is provided by the Genesys code
generation framework.
8.2 Control-Flow or Data-Flow Modeling?
The most substantial difference between workflow management systems is
typically the nature of their process models, that is, whether they express
the data flow or the control flow between the building blocks. In data-flow
modeling, the connections between building blocks are interpreted as data
pipelines, and execution control follows the data flow implicitly. In control-
flow modeling, the connections between building blocks define the flow of
control, and thus the data flow is modeled separately. While the nature of
the data-flow and control-flow specifications are essential for the semantic
interpretation of a workflow model, other features are usually less inherent
in the systems, and are thus more often subject to changes during further
development of the software.
The case study that is presented in this section (and which has in parts
also been discussed in the scope an encyclopedia article on bioinformatics
workflows [176]) aimed at examining the differences between data-flow- and
control-flow-based systems especially in the context of bioinformatics work-
flows. Therefore three increasingly complex reference workflows (details in
Section 8.2.1) have been selected that are suitable as benchmarks for the
modeling capabilities of the different software systems.
Table 8.2 surveys the workflow systems discussed in Section 8.1 with re-
spect to the nature of the workflow models, that is, whether they focus on
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