More and more within the last couple of years, there is a
recognition that the Web services composition concept will
constitute a major breakthrough and will revolutionize the
way we deal with integrating disparate and distributed computing
environments. Yet, to rise to such a position, a chief
concern is to guarantee a high-dependability level of the
Web services compositions, which is significantly critical,
specially in view of the particularities of the Web services
environment( unpredictability, heterogeneity, autonomy), if
confronted with other computing environments.
Our present work falls within this context since we tackle
the problem of QoS (Quality of Service) in the Web services
context by verifying to what extent fault-tolerant and
dynamically-executed Web services compositions are effi-
ciently serving their purposes. And in pursuing this goal, we
introduce a novel model that characterizes, estimates and
analyzes several QoS properties of dynamically-executed
fault-tolerant Web services compositionsnamely the reliability
and the execution time.
Our model allows acquiring more accurate estimations
since it confers a paramount importance to the repercussions
of failures. In addition, contrary to other QoS estimations
models in the Web services context, which use QoS
estimations published in UDDIs by the Web Services owners/
providers, our model computes QoS estimations on the
base of the compositions execution observations, where the
observation results are collected in a history.
Finally, since Web services are stateless, tracking the
failures and determining their locations is almost impossible.
To overcome this limitation, we propose to attach to
each of the composition’s component a state. In doing so,
obtained estimations can contribute in acquiring more accurate
information about the failures locations and can be
used later to improve the composition QoS in the future.
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