The Bio-jETI Framework - User-Level Workflow Design: A Bioinformatics Perspective - page 57

• The start conditions , that is, the set of data types that is available at

the beginning, are determined according to the preceding services using
data-flow analysis methods.

•

The end conditions , that is, the set of data types that have to be avail-
able at the end of the synthesized workflow are derived from input types
of the SIB at the destination of the loose branch. These so-called goal
constraints can be terminating (i.e., the search for solutions is aborted
once the required types are available) or non-terminating (i.e., the search
for further solutions continues beyond the state where goal constraint has
been fulfilled for the first time).

The domain-specific workflow constraints as provided by the domain
model and the problem-specific constraints as provided by the workflow
designer (see below) are also simply added to the specification formula.
The result of the synthesis algorithm is then in fact set of all constraint-
conform, executable concretizations of a loosely specified branch. Accordingly,
the four exemplary concretizations that are shown in Figure 2.13 (bottom),
where the draw and polaroid , and additionally also other services from the
corresponding domain model are inserted, are only some of the many possible
solutions for the synthesis problem defined by the loose specification above.
Note that although the examples applied in this topic comprise only single
loose branches to simplify matters, it is possible to mark arbitrarily many
branches in a workflow model as loosely specified. Then, the synthesis is
carried out separately for each branch, following their topological order in
the workflow model. As detailed in Section 9.2.1, improvements with respect
to precise constraint scoping and treatment of second-order effects (that occur
when the workflow model evolves during the synthesis) are however necessary
in order to fully support this feature.

•

Synthesis Execution

Depending on the configuration of the PROPHETS installation, the synthesis
is performed without further user interaction (i.e., in “silent” mode, where sim-
ply the shortest solution is taken), or with different intermediate steps where
the user can further customize synthesis inputs and parameters, and finally se-
lect an adequate result or refine the constraints in order to narrow the set of
solutions. In the scope of this work, a PROPHETS configuration has been used
that takes the user through the following synthesis steps, as summarized in Fig-
ure 2.14:

1. Edit constraints
Displays the domain-specific constraints that are already provided by the
domain model, which can be changed or removed. Additional problem-
specific constraints can be provided that narrow the workflow designer's
intentions further (using the template editor described earlier). As Fig-
ure 2.9 indicates, these problem-specific constraints are essential when