中文摘要：

随着云计算商业模式的成功推进，形成了三大主流的云计算服务模式：平台即服务、软件即服务和基础架构即服务。传统行业的供应商纷纷加入云计算的队伍。但由于激烈的竞争环境，使得云计算的标准化道路举步维艰，致使跨平台的交互和移植难以实现。同时，由于对不同的云平台没有形成统一可信的评价标准，使得众多的平台服务让用户无从选择。本文通过具体分析各种应用场景对跨平台服务的需求，得出构建“跨平台即服务”模式的必要性和必然性，提出利用可信第三方来实现“跨平台即服务”模式，给出跨平台的数据交互和移植行为在可信第三方监控下的规范化流程，并提出以可信第三方为中心的云平台安全和信誉评价标准，为企业选择合适的云平台提供参考。

英文摘要：

With the successful development of cloud computing business models, three major cloud computing service models have been formed： Platform as a service, software as a service and infrastructure as a service. The traditional industry providers eagerly moved to join the cloud computing research, but the intense competitions make it difficult to standardize the cloud compu- ting and to realize the interoperability and cross-platform migration. Meanwhile, the numerous cloud platforms resuh in that users do not know how to make their choice due to the different cloud platforms without a unified, credible evaluation criteria. In this paper, first, a detailed analysis of various scenarios on the demand for cross-platform services is given, which shows the necessity and inevitability of building a ＂cross-platform as a service＂ model. Second, by using the trusted third party to achieve this cross- platform as a service. We give the standard process of data exchange and migration in the cross-platform under the supervision of the trusted third party, and provide users with a credible third-party-centered cloud platform evaluation criterion of security and credibility. This will provide the valuable suggestions for enterprise to choose proper cloud platform services.