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

also mentions a type of static activity point which is defined by users at the buildtime
stage. The work in [23] selects an activity as a checkpoint if its execution time
exceeds the maximum duration while the work in [20] selects an activity as a
checkpoint if its execution time exceeds the mean duration. The state-of-the-art
checkpoint selection which satisfies the property of necessity and sufficiency is
proposed in [21] where minimum time redundancies for SC (Strong Consistency)
and WC (Weak Consistency) are defined. For example, an activity point is selected
as a WC checkpoint if and only if its execution time is larger than the sum of its
mean duration and its minimum WC time redundancy. The comparison result shows
that with the measurement of necessity and sufficiency, the one based on minimum
time redundancy has outperformed all the other checkpoint selection strategies.
Based on the minimum time redundancy based checkpoint selection strategies,
the work in [20, 22] further improves the efficiency of temporal verification by
utilising the temporal dependency between temporal constraints. The basic idea is
that with temporal dependency, the consistency of some later fixed-time constraints
can be deduced from previous ones. Then, based on temporal dependency,
was presented. With
CSS TD
CSS TD
, those subsequent fixed-time constraints whose
consistency can be deduced from previous ones will no longer take any checkpoints.
Accordingly, their verification can be avoided which otherwise incurred by other
strategies.
6.1.2 Problem Analysis
In order to save the overall cost, the practice of temporal violation handling is to
compensate the time deficits by light-weight (small time overheads and monetary
cost) violation handling strategies as much as possible instead of conventional
expensive heavy-weight temporal violation handling strategies such as resource
recruitment and workflow restructure, except for severe temporal violations with
excessively large time deficits. Therefore, in this chapter, the range of temporal
consistency states where light-weight temporal violation handling is effective needs
to be determined first, then statistically recoverable temporal violations can be
detected and handled at the early stage before they become severe or unrecoverable
(unrecoverable with light-weight temporal violation handling) temporal violations.
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