|Author:||Wong, Yu-chun Eugene|
|Title:||Xstream : a framework for efficient streaming of XML documents over wireless environment|
|Subject:||Hong Kong Polytechnic University -- Dissertations|
XML (Document markup language)
Streaming technology (Telecommunications)
|Department:||Department of Computing|
|Pages:||xi, 158 leaves : ill. ; 30 cm|
|Abstract:||XML (eXtensible Markup Language) has been developed and deployed by domain-specific standardization bodies and commercial companies. Studies have been conducted on a wide variety of issues encompassing XML. With regard to the use of XML for wireless and mobile computing, the focus has been on investigating ways to efficiently represent XML data for transmission over a wireless environment. The wireless environment has been known for its difference from its wired counterpart. In particular, bandwidth, latency, and error rates are all significantly poorer, varying and asymmetric in nature, features that lead to the sub-optimal utilization of a wireless link when it is used by Web applications. At the same time, data are currently fragmented in in-sequence order without taking into account the data's semantics and structure. All data fragments have to be received before the data can be processed. As the wireless environment has a higher error rate, there is a higher chance of losing data fragments. This delays the data processing. This thesis investigates the possibilities and issues around the use of generalized XML in a wireless computing environment and focuses on alleviating the shortcomings of the current approaches of fragmenting data. A middleware, Xstream (XML Streaming) is developed to fragment XML documents into autonomous units known as XDUs (Xstream Data Units). The concept of XDUs is fundamental in both the provision of efficient XML document transfers over a wireless link and in addressing the issues and challenges pertaining to wireless transmission. By fragmenting XML documents into XDUs, Xstream is able to incrementally send fragments over a wireless link, while enabling the receiver to perform look-ahead processing for the XML documents without waiting for the entire document to be downloaded. A fragmentation strategy is developed to fragment XML documents by taking into consideration their semantics and structural characteristics, along with the available wireless link bandwidth. A naming space which is adopted from a hierarchical namespace to identify an XDU so as to allow their flexible management is described. To alleviate the shortcomings consequent upon using TCP in a wireless environment, a transfer protocol, Xstream Transfer Protocol (XSTP) is developed to send XDUs over wireless links in XSTP packets, such that the XDUs can be processed as soon as they are received. Packetization strategies are proposed to optimize the occupancy of the available bandwidth by XDUs. A reassemble strategy has been devised for the receiving end, that allows XML documents to be incrementally reconstructed as XDUs are being received, while facilitating look-ahead processing by the client application. By adopting these concepts and strategies in Xstream, the efficient streaming of XML documents over a wireless environment by leveraging the rich semantics and structural characteristics of the XML documents, and by flexibly managing units containing XML data was realized. The various components of Xstream were implemented to reazlize its benefits. The Fragmentation Manager and the Reassembly Manager that realize the fragmentation strategy and the reassemble strategy were implemented. These components were tested separately to study the behaviour of the approaches. The Xstream Transfer Protocol was also implemented to realize the packetization strategy and the streaming of XDUs. The experiments were conducted in an emulated environment to study the performance of Xstream. In an end-to-end scenario, streaming XML over wireless environment using Xstream was found to be more efficient than using conventional connection-oriented transport protocol.|
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