XML Access Control Based on Security Views

web上数据的性质和XML的灵活性导致用XML编码的数据是半结构化的。大量异构分布式数据的可用性需要集成来自多个XML源的XML数据。XML数据源可以基于或不基于模式、DTD（文档类型定义）模式、XML模式或由不同公司提出的任何其他模式。由于网络上可用数据的性质，可能包括医疗保健系统中的患者数据、银行业中的员工数据或任何大型组织或大学系统中的学生数据，所有这些都需要保护数据。这进一步要求具有访问权限和特权的授权用户能够访问所需的数据，以便有效地完成他们的工作。为了向具有给定访问权限的授权用户提供对XML数据的安全访问，需要开发一种细粒度访问控制机制，以提供对文档树的部分或树中的某些节点的访问。为了实施这样的访问控制模型，需要XML Schema的可用性，该Schema指定了可访问XML数据的结构，因为模式提供了数据交换、集成、查询公式和优化的机制。本研究的目的是开发使用XML Schema定义安全规范的机制，并在查询处理期间有效地实施这些约束。这些约束的实施将基于安全视图。安全视图表示原始文档的受限制视图，以及可以根据安全规范派生的伴随XML Schema。此外，安全视图将只向具有访问权限的授权用户公开所需的模式结构和文档内容。授权用户将能够在XML Schema的安全视图上提出查询，以形成他们的查询。

The nature of data on the web and the flexibility of XML have resulted in data encoded in XML to be semistructured. The availability of large amounts of heterogeneous distributed data necessitates integrating XML data from multiple XML sources. The XML data sources may be based either or no schema, DTD (Document Type Definition) schemas, XML Schema, or any other schema that has been proposed by different companies. Due to the nature of data available on the web that may include patient data in a healthcare system, employee data in a banking industry or any big organization or student data in a university system, all require securing the data. This further necessitates that authorized users with access rights and privileges are able to access the required data in in order to accomplish their jobs efficiently. In order to provide secure access of XML data to authorized users with given access privileges requires the development of a fine grained access control mechanism to provide access to either parts of a document tree or certain nodes in the tree. To enforce such access control models requires availability of XML Schema that specifies the structure of accessible XML data as the schemas provide the mechanism for data exchange, integration, query formulation and optimization. The objective of this research is to develop mechanisms to define security specifications using XML Schema and to effective enforce such constraints during query processing. Enforcing of these constraints will be based on security views. Security views represent a restricted view of the original document and the accompanying XML Schema that can be derived based on a security specification. Further, a security view would expose only the required schema structure and document content to authorized users with access privileges. Authorized users will be able to pose queries over the security view of the XML Schema to formulate their queries.