关系模式到XML Schema的约束保留映射

随着XML逐渐成为网络数据表示和交换的标准，将关系数据描述为XML格式已经成为一种趋势。针对这种情况，提出了关系模式到XML Schema的保留约束映射算法，通过对关系模式和XML Schema数学建模，定义模式映射模板，将关系模式转化为XML Schema模式的描述，实现关系数据到XML文档的转化。由于在数学建模过程中充分保留了语义约束信息，与同类研究相比，算法的映射结果可以更完整的描述关系模式的结构和语义信息，保证了数据的连贯性。

A New Translation Algorithm Based on Constraints-Preserved Mapping from Relational Schema to XML Schema

Although some translation algorithms from relational schema to XML DTD (Extensible Markup Language Document Type Definition) exist, they are unsatisfactory when more expressive and coherent results are required because of the inherent limitations of XML DTD. We now propose a better and new translation algorithm based on W3C XML Schema standard and on what we call constraints preserved mapping, which are the keys to the architecture proposed in our recent paper . In our approach, we define a data model based on directed graph theory, which we name DGDM (directed graph data model); we utilize it as an intergradation data model for schema translation to narrow down the areas of structure inconsistencies between flat relational schema and hierarchical XML Schema. Because XML Schema is more complex than relational schema and because there is no need for full model XML Schema, we construct a predigested model for XML Schema that conforms to graph structure as well; we name this predigested model XML Schema Template. By using DGDM and XML Schema Template, our algorithm not only has capability to capture the full structures and semantic constraints in relational schema, but also makes translation easy because of the similarity in structure of DGDM and the XML Schema Template. We also show how DGDM can be used to automatically derive structures and semantic constraints in relational schema, how the relational schema can be easily transformed into XML Schema by the translation between DGDM and the XML Schema Template, and how the semantic constraints can be well preserved. We give some experimental results that demonstrate preliminarily that our new translation algorithm is indeed better than those based on XML DTD.