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

violations can still be recovered by light-weight automatic handling strategies.
As discussed in [17], similar to TDA, the basic idea of PTDA is to automatically
utilise the expected probability time redundancy of the subsequent workflow
segments to compensate the current time deficits. ACOWR, as one type of workflow
rescheduling strategies, is to tackle the violations of QoS constraints through
optimising the current plan for Task-to-Resource assignment [62]. When temporal
violations are detected, these strategies can be realised automatically without human
interventions. Furthermore, PTDA produces only a small amount of calculations.
ACOWR, as a type of metaheuristic searching algorithm, consumes more yet
acceptable computing time but without recruiting additional resources. Therefore, as
will also be verified through the simulation experiments demonstrated in Section 8.6,
PTDA, ACOWR and the hybrid strategy of PTDA and ACOWR are effective
candidates for handling temporal violations given the requirements of both
automation and cost-effectiveness as presented in Section 8.1.2.
In the following, we present the algorithms for the three temporal violation
handling strategies.
PTDA for Level I Violations
TD( a p
)
WS ( a
p+
1,
a
p+
1,...
a
p+
m
)
( a p + 1,
a p m
)
2
M{
µ , σ }
i i
U
+
{ U′
( a ) | i = p + 1,... p m};
U i +
p+
m
∑
p+ 1 , a p+
m ) = U ( a p+
1,
a p+
m ) − ( µ i + λθ
* i )
i=
p+
1
TR( a
σ
i = p +1
U '
( a ) U( a )
3σ
p + m
i = i − TR(
a p+
1,
a p+
m ) *
p+
m
∑
i=
p+
1
( a )
( ai
) − M ( ai
)
( D(
a ) − M ( a ))
D
σ
i
= U
i
− TR(
a
p+
1
, a
p+
m
) *
p+
m
∑
i
i=
p+
1
D( a i
) µ
i
+ 3σ
i
a i
=
( σ )
= M ( ) µ
i
{ U ′( a ) | i = p + 1,...
p m}
U
i
+
i
Figure 8.6 PTDA Algorithm
i
The basic idea of PTDA is the same as TDA presented in Section 8.2.1. However,
since in this thesis, the time deficits are calculated based on our probability based
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