Service Layer providing cloud services. IaaS is considered a service providing infrastructure along with PaaS offering middleware and SaaS providing applications.

服务层，提供云服务，如IaaS提供基础设施服务，PaaS提供中间件服务，SaaS提供应用服务。

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The middleware layer can be thought of as a pure service layer.

中间件层可以被认为是一个纯粹的服务层。

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In hybrid form, a private cloud can include data stored on premise or off, with a private Platform-as-a-Service middleware layer managing application data and enforcing data security.

FORBES: The Data Protection And Security Case For Private Clouds