Xiao Liu PhD Thesis.pdf - Faculty of Information and Communication ...

expected time redundancy of subsequent activities, i.e. self-recovery. For a
necessary and sufficient checkpoint where a temporal violation is detected, the
occurred time deficit and the expected time redundancy of subsequent activities after
the checkpoint are the basic factors used to decide whether a checkpoint should be
selected as a temporal violation handling point or not. Therefore, an effective
strategy is required to estimate the probability of self-recovery so as to facilitate
temporal violation handling point selection in scientific workflow systems.
7.2 Adaptive Temporal Violation Handling Point Selection Strategy
7.2.1 Probability of Self-Recovery
The details of the probability based temporal consistency model are presented in
Section 5.2 and hence omitted here. Given the probability based temporal
consistency model, we can quantitatively measure different temporal violations
based on their probability temporal consistency states. Furthermore, at a specific
checkpoint, the occurred time deficit and the expected time redundancy of
subsequent activities need to be estimated. They are defined as follows.
Definition 7.1: (Probability Time Deficit).
At activity point
a p , let U (SW ) be of β % C with the percentile of λ β which is
below the threshold of θ % with the percentile of λ θ . Then the probability time
deficit of U (SW ) at a p is defined as
PTD U(
SW),
a ) = [ R(
a1,
a ) + θ ( a + 1,
a )] −u(
SW)
. Here,
( p
n
k
k = p+
1
θ(
a + 1,
) = ∑ ( µ + λθ σ ) .
p a n
k
p
Definition 7.2: (Probability Time Redundancy for Single Workflow Segment).
At activity point
p
a p , let U (SW ) be of β % C with the percentile of λ β which is
above the threshold of θ % with the percentile of λ θ . The subsequent activities are
defined as those activities from the next activity of the checkpoint, i.e. a p+ 1, to the
n
end activity of the next temporal constraint, e.g.
a p + m . With a segment of size m
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