Dr. Xiujun Ma Profile

Dr. Xiujun Ma

at Peking Univ

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Publications (2)

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Proceedings Article | 6 August 2007 Paper

A cooperated P2P GIS for loose coupled governmental application

Chenyu Li, Kunqing Xie, Xiujun Ma, Cuo Cai, Yanfeng Sun

Proceedings Volume 6754, 67542Y (2007) https://doi.org/10.1117/12.765232

KEYWORDS: Geographic information systems, Databases, Distributed computing, Computing systems, Human-machine interfaces, Prototyping, Data modeling, Telecommunications, Lithium, Internet

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Current governmental applications are of large scale and always compute-intensive and data-intensive, and we focus on introducing P2P computing to facilitate loose coupled governmental applications in this paper. As GIS data is always deposited in locationally distributed nodes, which are probably administrated under spatial databases, the global range is divided into regions to eliminate complicated consistency maintenance and unnecessary message exchanging, and hierarchical spatial indexes are designed for efficient locating spatial resources and low control cost. When executing, a user submitted global spatial query are firstly parsed to sequential subtasks refer to distributed spatial index, and then dynamically passed to appropriate nodes and cooperatively accomplished. Nodes intercommunicate by cooperating messages, which are sent directly to the destination. Besides collaboration process of sequential execution, a dynamic alternative participant approach for failure handling of the sequential execution is provided, which saves the expensive rollback or abort. And this paper also designed and implemented a p2p based loose governmental application prototype, in which nodes intercommunicate via p2p network sub layer, also a user interface is implemented to manage the request from user and eventually reply a result.

Proceedings Article | 26 July 2007 Paper

Modeling and query the uncertainty of network constrained moving objects based on RFID data

Liang Han, Kunqing Xie, Xiujun Ma, Guojie Song

Proceedings Volume 6752, 67523Y (2007) https://doi.org/10.1117/12.761305

KEYWORDS: Data modeling, Global Positioning System, Spatial filters, Databases, Roads, Statistical analysis, Motion models, Intelligence systems, Internet, Geoinformatics

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The management of network constrained moving objects is more and more practical, especially in intelligent transportation system. In the past, the location information of moving objects on network is collected by GPS, which cost high and has the problem of frequent update and privacy. The RFID (Radio Frequency IDentification) devices are used more and more widely to collect the location information. They are cheaper and have less update. And they interfere in the privacy less. They detect the id of the object and the time when moving object passed by the node of the network. They don't detect the objects' exact movement in side the edge, which lead to a problem of uncertainty. How to modeling and query the uncertainty of the network constrained moving objects based on RFID data becomes a research issue. In this paper, a model is proposed to describe the uncertainty of network constrained moving objects. A two level index is presented to provide efficient access to the network and the data of movement. The processing of imprecise time-slice query and spatio-temporal range query are studied in this paper. The processing includes four steps: spatial filter, spatial refinement, temporal filter and probability calculation. Finally, some experiments are done based on the simulated data. In the experiments the performance of the index is studied. The precision and recall of the result set are defined. And how the query arguments affect the precision and recall of the result set is also discussed.

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