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The lack of standard or common API among heterogeneous PaaS platforms makes cloud developers locked inside a specific PaaS platform and not able to easily migrate their applications or data. One approach for application portability is to implement applications using a generic API and develop an adapter for each specific PaaS platform. Whereas the generic API provides cloud developers with a set of generic methods, each adapter translates these generic methods into their corresponding specific-API calls. However, updates to a specific API (e.g., renaming methods or changing input parameters) may require re-factoring or even re-implementation of its corresponding adapter; otherwise code that uses the adapter will not run correctly with the new API. We use the term API synchronization to name this problem. The work in this paper addresses the API synchronization problem, whereby a method for automatic adapter generation that is based on semantic annotations and semantic search is presented. The proposed method requires that the specific-API methods are annotated to describe the conceptual meanings of method inputs and outputs based on a common domain ontology. The proposed method was evaluated using a case study for a generic API of the blob storage service. The automatically generated adapters of the blob storage service were used to implement a generic application and to deploy it on two different PaaS platforms, namely Google App Engine and Windows Azure. |
