Content based dissemination of XML data

Abstract

The Internet has considerably increased the scale of distributed information systems, where information is published on the Internet anywhere at anytime by anybody. To avoid overwhelming users with such huge amount of information, content-based dissemination systems have emerged, where users subscribe a set of queries to the system to express the kinds of information they are interested in and the dissemination system will automatically deliver newly published information to the proper users. With the emergence of XML, it quickly becomes the standard for data exchange on the Internet. There is a new trend to publish the data contents in XML format and to provide users with a more expressive subscription language as such XPath to address both the content and the structure of the data, which makes the content-based dissemination of XML data increasingly important. This dissertation focuses on content-based dissemination of XML data systems. The effectiveness of such dissemination systems involves two aspects, i.e. the efficiency of the system and the functionalities that they provided. The adoption of XML data in the system increases the complexity of subscription matching at each router. While various approaches have been proposed to improve filtering efficiency, these approaches focus on optimizing the filtering locally at each individual router. In this dissertation, a global optimization approach is proposed that uses the piggybacked annotations to enable collaborative filtering among routers. With respect to the functionalities provided by the system, this dissertation focuses on resolving two limitations of existing dissemination systems. Firstly, due to the limitation that only complete XML documents are handled in current dissemination systems, this thesis presents a three-step approach to match a set of XPath-based subscriptions on fragmented XML data in content-based dissemination, which is to satisfy the requirements for the resource-constrained mobile devices or sensors for accessing data in terms of XML fragments. Secondly, due to the implicit assumption that all published information within the same domain conforms to the same DTD in current dissemination systems, this thesis introduces a data-rewriting architecture to resolve the heterogeneous schema problem in the content-based dissemination of XML data. We have implemented these approaches, and conducted extensive experimental studies to demonstrate the efficiency and effectiveness of these approaches. We believe that our research helps to significantly improve the efficiency and to effectively extend the functionalities of the content-based XML data dissemination system, which makes this system more practical and useful.