Contract of the orchestration Sample Clauses

Contract of the orchestration. We take the contract of a service S, FS to be a probability distribution of the response time. Expecting a service provider to able to give a precise probability for every possible value of latency is however impractical. So, we take the contract with provider S to be a set of quantiles of latencies {x1 . . . xk} with the corresponding probabilities {FS(x1) . . . FS(xk)}. Hard 2Actually, we do not need to shift the window by 1; any fixed amount can be used instead provided that successive windows overlap. contracts are just a special case of our soft contracts, in which only one such quantile exists. We thus requires the provider to pass from promising a performance probability of one quantile to multiple quantiles. { } During simulation, two possibilities may be considered when using FS = FS(x1) . . . FS(xk) for sampling response times: { } • Use FS as it is, by sampling each time one of the quantiles x1 . . . xk , in proportion with FS. This would lead to over-pessimistic distributions, however. • Hypothesize a constant probability density within each quantile, except for the last one where exponential distri- bution is hypothesized. From our experiments regarding web services response times, we preferred this second approach. While monitoring, we check for violation of condition (8) only for the set of quantiles that have been promised by the service S in its contract FS. The set of positive reals R+ in equation { }