Research On XML-Based Heterogeneous Data Sources Integration

XML has emerged as the standard for information exchange and data between Web applications. As a kind of tag language with self-describing characteristic, XML can express any information of heterogeneous sources flexibly according to specified application. Through researching on integrity constraints for XML, this paper presents a middleware of heterogeneous sources integration based on XML.Little previous work has addressed the issue of DTD conformance and constraint satisfaction for XML-based data integration. So, this paper gives two XML semantic constraints, Lr and Loo. Lr derives from the constraints of RDB. It includes key constraint and inclusion constraint. Loo comes from OODB. It has key constraint, ID constraint, foreign key constraint, set-valued foreign key constraint and inverse constraint. Then, define a universal constraint, Lo-r.This paper introduces a method of integration only for relational data, AIG (Attribute Integration Grammar). AIG extends a DTD by semantic attribute, semantic rule and constraints. The novelty of AIG consists in semantic attributes and their dependency relations for controlling context-dependent. This paper uses this for reference and presents an AIGO based on OODB. The middleware realizes AIG and AIGO and gives the algorithms for it implementation.Query decomposition also plays an important role in implementation of our middleware. Global query is submitted through XQuery, a mature query language for XML and then XQuery needs to be decomposed. To implement query decomposition, this paper presents a concept--path schema. A path schema is just like an attribute in relational table. Through referred to some concepts of multidatabase system, such as schema mapping tree, query tree, give the schema mapping tree and query tree basedon path schema and the algorithms of query decomposition.