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Fig. 1.9 Semantic handling of workflows
type-correct (cf. the compatibility example above), the workflow as a whole
is not admissible, as there is a constraint in the domain model which says
that “To make a birthday card, the ImageMagick convert draw and polaroid
services must be applied to a picture.”.
The four-step workflow at the lower part of the figure is both type-correct
and constraint-conform. Instead of being constructed by the user step-by-
step until all constraints are fulfilled, it can also be created automatically by
exploiting the semantic information provided by the domain model: The in-
correct workflow model above can be treated as abstract workflow description
that specifies basic information about the intended workflow, in this case two
of the services that are to be used. In combination with the interface descrip-
tions of the services in the domain (in terms of their inputs and outputs), the
semantic type information and the additional constraints that express further
domain knowledge, this incomplete workflow specification can automatically
be concretized into a correct and executable workflow.
1.1.3 Technical Consequences
The previous sections identified the primary requirements for a user-level
workflow management system as a model-based, service-oriented workflow
development environment that is enhanced by semantic methods. This section
is concerned with the corresponding concrete technical consequences. In fact,
the requirements for scientific workflow systems that are listed in the following
are in good alignment with commonly agreed requirements for this kind of
system, as described, for instance, in [115, 166, 27, 242, 128, 37, 332] in general
and in [256, 120, 258] with particular regard to semantic service environments:
Requirement 1: abstraction from programming details
First of all, abstraction from programming details is essential in order to
provide an orchestration level that allows users to cope with the scientific
aspects of the experiments rather than with the underlying technology [242].
 
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