Multi-tiered And Bi-directional Data Integration Between XML And RDB

A Dual Data Management Mechanism (DDMM for short) for XML (Extensible Markup Language) and RDB (Relational Data Base) is proposed in this paper. In DDMM, the RDB is taken as the bottom storing medium and the upper XML view is set up for data exchange and direct application under Internet/Intranet environment. Based on DDMM, the multi-tiered and bi-directional data integration technique between XML and RDB, is studied systematically and in detail, and the reciprocal data accessing and exchange between RDB and XML is carried out on respectively three levels: static data transformation, dynamic data query and synchronized data update.The infrastructure for manufacturing informationlization will certainly be Internet/Intranet, and XML has been a factual standard for data representation under Internet/Intranet environment. However, currently in enterprises, most data is still stored in traditional RDB. How to integrate XML and RDB to realize the reciprocal data accessing and exchange has become one of pivotal problems to be resolved. Aiming at this problem, the main research issues and achievements in this paper are as follows:Bi-directional Data Transformation between RDB and XML with Semantic Constraints Preserved For most of existing researches on static data transformation between XML and RDB, DTD is taken as the schema description language for XML, and the semantic constraints are often lost during the transformation process. To overcome these disadvantages, the author adopts XML-Schema, a standard schema description language proposed by W3C to replace DTD, as the description method owing to its more powerful functions than DTD, and of course with the syntax much more complicated. After analyzing the constraints characteristics in both XML-Schema and Relational Schema, a semantic constraints-preserved algorithm is proposed which can realize the bi-directional schema mapping between RDB and XML through a formalized description of XML based on regular tree and a general expression for relational schema based on direct graph approach. Thus, the holistic data transformation is implemented between RDB and XML and their integration on the static transformation tier is achieved. With this integration, a mass of legacy data stored in RDB can be published as XML, and the XML data can also be stored into RDB. As the basis of the DDMM, the static data transformation mechanism proposed allows users to operate the bottom data in RDB by querying or updating through the corresponding XML view.Dynamic Data Query on Bottom RDB through XML View Using XQuery XQuery is the most suitable language for query in XML as its powerful expression ability. However, few of essential research progresses have been made because of its complexity and hugeness. Furthermore, the existing algorithms fordynamic query are generally dependent on the static mapping algorithms. To resolve these two problems, a GVRS (General Virtual Relational Schema) model for XML Document is put forward as a bridge between XML instance document and factual RDB, and an algorithm which transformes XQuery into SQL and is independent on the static schema mapping, is realized. Based on the above approaches, the dynamic data query on bottom RDB is carried out through XML view and the data integration between RDB and XML is achieved on the dynamic query tier. The users can dynamically query the bottom data as needed.Synchronized Update between XML View and Bottom RDB Up tonow, the updating on XML as well as the synchronized updating on integrated XML and RDB have not been studied systematically. The author proposes a protocol of XML Update Language (XUL) and also studies the technique on syntax merging between XUL and XQuery. By implementing the transformation from XUL to SQL and setting up a synchronized operating mechanism, the consistency between XML view and the bottom RDB is assured. To improve the effectivity of the synchronized updating, a concept called "active update" is introduced and the related key technologies such as XML change detecting and...