Mots-clés : Services de données, coordination de services, optimisation de requêtes, Service Level Agreement, workflows
In this work we tackle the problem of optimizing hybrid queries over data produced by data services either on-demand or continuously. Such queries are implemented by query workflows that coordinate data and computing services. The execution of query workflows has to respect Service Level Agreement contracts that define the optimization objective in terms of the expected quality of service. The optimization objective is described by a vector of weighted cost attributes such as the price, the time, the energy, etc. The weights define the preferences among the cost attributes for enabling the comparison among query workflows.
In this context, the hybrid query optimization is about to find the query workflow that best conforms the SLA contract. Our approach for generating the search space of query workflows, the cost estimation, and the solution space is therefore oriented to satisfy SLA contracts. Our main results are: (1) the generation of the search space considering both control-flow and data-flow of query workflows, (2) a cost function that considers the absence of data-related parameters, and (3) the adaptation of a top-k algorithm for selecting the suitable query workflows for a given SLA.