The computational complexity of QoS measures for orchestrations

Abstract

We consider Web services defined by orchestrations in the Orc language and two natural quality of services measures, the number of outputs and a discrete version of the first response time. We analyse first those subfamilies of finite orchestrations in which the measures are well defined and consider their evaluation in both reliable and probabilistic unreliable environments. On those subfamilies in which the QoS measures are well defined, we consider a set of natural related problems and analyse its computational complexity. In general our results show a clear picture of the difficulty of computing the proposed QoS measures with respect to the expressiveness of the subfamilies of Orc. Only in few cases the problems are solvable in polynomial time pointing out the computational difficulty of evaluating QoS measures even in simplified models.

Web Apps and Imprecise Probabilitites

“…The following example attempts to to grasp the relation between our approach and imprecise probabilities. Our next result provides a generalization of a similar result in [7]. We are able to include asymmetric parallelism in the bag semantics and devise a normal form.…”

“…When it is clear from the context that S is faulty, we denote S F shortly as S. [7]. Assuming independence among executions, the probabilistic behaviour is given in the following table:…”

“…We can show that when there is no asymmetric parallelism (no indeterminism) probabilistic information can be carried out through constructors. Based on the approach given in [7], we can shown the existence of a normal form.…”

“…To reason about a program, we need a semantics to assign meaning [6]. Bag semantics was introduced in [7] to give a precise description of the approach taken in Example 1. In such approach we abstract from return time.…”