Spatio-temporal Databases / Location-based Services

Demo System: PLUS: A Message-Efficient Prototype for Location-Based Applications

The PLUS system is designed to efficiently track moving object locations on a road network and execute continuous spatial queries in support of location-based services. PLUS implements a novel lazy position update mechanism that significantly reduces the communication overhead and server indexing load related to frequent location updates in moving object and moving query scenarios. The contribution of this demo is to present how the lazy position update scheme can achieve message-efficiency under various conditions which can be interactively set via user-selectable parameters in a graphical user interface.

Application Areas:

Rescue missions

  • Tracking
  • Locating nearby facilities
  • Dispatching rescue teams

Taxi services

  • Locating users
  • Locating nearby available taxis
  • Quick response to service calls


  • Highly dynamic environments where both query and data objects are moving require frequent mobile-server message exchange.
  • An effective query result update mechanism is expected for continuous queries.
  • A large number of users may request a location-based service at the same time.
  • A fast response time for reporting the current query result is difficult to provide when considering a very large dataset.
  • Users may move arbitrarily and change velocity over time.

People Involved:

  • Yuling Hsueh
  • Roger Zimmermann
  • Wei-Shinn Ku
  • Haojun Wang
  • Chung-Dau Wang



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