XML Data Transformation and Integration — A Schema Transformation Approach

The process of transforming and integrating XML data involves resolving the syntactic, semantic and schematic heterogeneities that the data sources present. Moreover, there are a number of different application settings in which such a process could take place, such as centralised or peer-to-peer settings, each of which needs to be considered separately. In this thesis, we investigate the problem of data transformation and integration for XML data sources. This data format presents a number of challenges that require XML-specific solutions: a schema is not required for an XML data source, and if one exists, it may be expressed in a number of different XML schema types; also, resolving schematic heterogeneity is not straightforward due to the hierarchical nature of XML data. We propose a modular approach, based on schema transformations, that handles the distinct problems of syntactic, semantic and schematic heterogeneity of XML data. We handle the problem of syntactic heterogeneity of XML schema types by introducing a new, automatically derivable schema type for XML data sources, designed specifically for the purposes of XML data transformation and integration. We show how semantic heterogeneity can be handled in our approach using existing methods, and we also propose a new semi-automatic method for resolving semantic heterogeneity using mappings to ontologies as a ‘semantic bridge’. We then present a new schema restructuring method that handles schematic heterogeneity automatically, assuming that semantic heterogeneity issues have been resolved. The contribution of this thesis is the investigation of the problem of XML data