一个开放可扩展的SDAI实现系统

STEP标准数据存取界面－SDAI为应用程序提供了独立于数据存储的STEP数据访问界面，SDAI允许访问不同的数据存储系统，有不同的实现语言联编方式，如果对每一种实用语言和数据存储系统单独实现SDAI，其工作量将是巨大的，该文选择系数据库作为SDAI数据存储系统，C语言作为实现语言，实现系统独立于不同的关系数据库系统，并且为不同语言的联编提供了一个统一的开发平台，提高了系统的开放性和可扩展性，为STEP在企业信息集成中的应用提供了核心操作，STEP建模语言EXPRESS，关系数据库，SDAI实现语言在模式表示上的不匹配是系统实现要解决的主要问题，该文从数据字典，STEP数据的字储与访问等方面阐明了系统实现时没模式之间的匹配过程。

Implementation of An Open and Extensible SDAI System

Standard Data Access Interface (SDAI) in STEP isolates the application program from the underlying data storage system. SDAI contains a functional definition part and several specific programming language bindings. While providing a standard way to the sharing of product data among different applications,SDAI leaves various implementation strategies to SDAI implementors. One critical issue is the implementation cost. There are various STEP application protocols,programming languages, as well as data storage systems for an implementor to choose from. Changes of any of these three aspects will lead to significant modification or even re implementation of an existing SDAI system. Dictionary based SDAI late binding will reduce the cost to implement multiple application protocols. It is the consideration of the implementor to reduce the cost increasing raised by the other two aspects. This paper describes an architecture to implement SDAI late binding on relational database systems. The architecture has a database layer to make it portable among various relational database systems,a core STEP object operation layer to provide reusable modules for different implementation languages,a data dictionary to facilitate late binding,and finally,the standard data access interface which will be called by application programs. The interfaces between these layers are identified. To store STEP data in relational database systems,we also discuss the translation of EXPRESS data models to relational data models. To distinguish between SDAI data schemas and application data schemas,we manage SDAI data schemas such as session schema in the SDAI layer,and application data schemas in the core STEP objects operations layer. We implement SDAI C late binding on Oracle based on the architecture and we will implement other SDAI language bindings on the architecture with relatively lower implementation cost.