
Complex Distributed Scenarios as Workflow Applications 43
2.2.5 Workflow Scheduling
For abstract workflows that contain tasks with two or more services as-
signed to them, a workflow scheduling problem needs to be solved. Given
the aforementioned dependency constraints defined by the graph, using the
introduced notation, the workflow scheduling problem can be stated as
follows:
∀
i
find t
i
→ (s
i sel(i)
, t
st
i
) (2.1)
where s
i sel(i)
denotes the service selected for execution of t
i
starting at time
t
st
i
such that
∀
i,k:(t
i
,t
k
)∈E
t
st
k
≥ t
st
i
+ t
exec
i sel(i)
(2.2)
with constraints on the workflow execution time and cost. The workflow ex-
ecution time (not considering scheduling ...