The core concept of the model Driven Architecture — which can solve or alleviate the problems mentioned above — is the platform-independent model. Essentially, the MDA has three tiers.

模型驱动架构的核心概念——可以解决或减少上面提到的问题——是平台无关模型(platform - independent model)。

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The framework of the system adopt three tiers architectures, based on B/S model.

该系统采用了基于B/S模式的三层架构作为系统实现的体系结构；

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This model is composed of three tiers: data tier, application tier and presentation tier.

模型框架结构分为数据层、应用服务层和视图层。

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The maturity model shown in this pyramid is used to help position EECM solution vendors into one of three tiers, with additional criteria including range of functional coverage, available resources and reference accounts.

FORBES: Research Summary: Enterprise Energy & Carbon Management Solutions