Cloud Computing is an emerging business model to provide access to IT resources in a pay per use fashion. Those resources range from low-level virtual machines, passing by application platforms and ending in ready to use software delivered through the Internet, creating a layered stack of differentiated services. Different cloud vendors tend to specialize in different levels, offering different services each with its own proprietary API. This clearly led to provider lock-in and hinders the portability of a given application between different providers. The goal of this paper is therefore to provide an abstraction of the different levels of services in order to reduce vendor lock-in and improve portability, two issues that we believe impair the adoption of the Cloud Computing model
