Research On Scheduling Technique Of XML Data Broadcast In Wireless Environment

In recent years, there is an increasing interest of using mobile devices (e.g., PDAs, palmtops, cellular phones, etc.) to gain information in wireless environment. Data broadcast is an efficient way for information delivery, as it allows an arbitrary number of mobile clients to access data simultaneously. The types of broadcast data are boundless, including live news, stock quotes, and traffic information.XML has gained a great of popularity as the de facto standard for data integration and an effective format for data exchange. Most Internet browsers provide support for XML in their later versions and many the major IT companies have integrated XML into the software products. Therefore, broadcasting XML data via wireless channel is a novel research issue, which attracts interest of many researchers.Traditional broadcast data are formatted as<key, value> like records in relational database, and mobile users retrieve the data item by its key value. While in XML data broadcast, mobile users submit XPath queries and the matched result are parts of XML documents. Thus, the retrieved XML data may have redundant information. These redundancies can be devided into two categories. Useless redundancy refers to the information not matched users queries and reduplicate redundancy refers to the reduplicate information among XML documents.In this paper, we focus on research of the fragmenting methods for skewed XML data access in push-based broadcast to resolve the useless redundancy. Firstly, a novel organization of XML data named subtree-level scheme is proposed. Each XML document is fragmented to pieces according to the access probability of each node. Secondly, we put forward two efficient fragment algorithms:horizontal fragment algorithm and threshold fragment algorithm. Finally, we prove that the two-tier index can be adopted in subtree-level scheme by a little modification.For reduplicate redundancy, we propose a document-merge algorithm. An effective affinity of XML documents is derived by analyzing the effect of merging documents. Redundant information will be reduced by recursively merging the documents with the largest affinity.The experiment shows that our algorithm will enhance the effective of broadcast and saving the limited bandwidth.