Comparing SLAs for Cloud Services: A Model for Reasoning

Abstract

Nowadays cloud services are gaining their momentum. A Service Level Agreement (SLA) represents an agreement between a service provider and a customer for a particular service provision. Cloud providers and services are often selected more dynamically than in traditional IT services. Hence, services need to be compared according both to technical aspects and the promised SLAs, but no widely accepted model, standard or best practice, that would lead to a more rigorous SLA comparison, are currently available. In this paper, we present a conceptualization of SLAs including the explicit modeling of formulas for service level indicators, and its corresponding open, reusable ontological representation. On its top, we provide operators for analysis and comparison of SLAs, relying on a reasoning framework in Logic Programming capable to manipulate indicator formulas and other SLA features. We provide an evaluation by considering a cloud scenario where several SLAs have to be compared.