Location aware application framework
The explosive growth of the use of intelligent mobile devices (mobile phones and PDAs) opens up new possibilities for delivering location information to the mobile devices, and delivering services to the mobile devices that are customized and tailored according to their current location. Currently, we are observing a convergence of the PDAs and the mobile phones. The PDAs are acquiring advanced wireless communication capabilities; and the mobile phones are getting more computation and Internet access features. In the near future most appliances will also have network interfaces and remote management capabilities. These advances, together with inexpensive position sensing devices will make location-aware applications popular. However, due to the lack of an appropriate "location-aware application development framework", many basic services will be implemented in each of the applications and cooperation between different location-aware applications will be difficult.
Applications today do not take into account the location information of the clients or the service providers. By providing an infrastructure that captures the mapping of services in an area of interest (we call them "regions") and also a mapping of clients in the regions, applications can aggregate the location information from a variety of remote sensing technologies and provide a single, seamless interface to it. With this type of information it is feasible to enable innovative location-aware applications. Delivering location-dependent services to mobile devices requires the following components: storage of location information and delivery of spatial data to mobile devices.
Locating and organizing location dependent services
Providing services to mobile devices is more than just converting Web information to match the capabilities of the device (small screen, low bandwidth, etc.). A typical Web portal, as provided by companies such as Yahoo or as provided internally by corporations to their work force, is loaded with as much information as possible, usually in the form of jumping-off points to other information repositories. This approach is too limited once one considers mobile devices that, by definition, can be anywhere. However, once one adds the capability for the Web server to recognize the geographical location of a mobile device, the server can then adapt it self and provide services or information that are relevant to the current location.
Extending this model, one can see that large number of services can then be built all with content that is more or less local to specific locations: for example, a service monitors local buses and trains, while another monitors inter-city trains and commuter airline traffic. The model can extend to local restaurants advertising their menu, hotels with room availability, theaters that have last-minute tickets for sale, etc. Further along the line, services could themselves be physical devices that just advertise their availability: public printers on a campus, ATMs, vending machines, etc. Clearly, in such a model, the number of services potentially relevant for a given location can grow enormously and be very dynamic, with new services appearing and disappearing constantly.
Our current line of thought is to associate services with geographical areas or "regions". A region can of course be defined as a member of a hierarchical structure (country, state or province, county, city or municipality, district, street, etc.). However, this model is too simple to represent the reality, where regions are likely to be defined in more flexible ways, crossing over the hierarchical boundaries. Examples can be metropolitan areas that spread over state or country boundaries, or company-specific sales areas that cover areas over multiple counties. The services provided by the spatial database can be used to define new service regions based on some spatial and non-spatial attributes. For example, a spatial union operator can be used to combine multiple existing service areas into a new service area. The spatial buffer operator can be used to construct a new service area based on some distance metric.
Conclusions
Recent reports have described the accomplishments of spatial database research and have prioritized the research needs in this area. Gueting (1994) and Worboys (1995) provide a broad survey of spatial database requirements and an overview of research results. Kim et. al. discussed the research needed to improve the performance of spatial databases in the context of object relational databases. The primary research needs identified were SQL support for spatial types, support for spatial indexing methods, development of cost models for query processing, and the development of new spatial join algorithms. Many of the research needs identified in this report have since been addressed.
Current spatial database systems provide support to store and retrieve geometric properties of spatial features. They also provide indexing support and operational support like topological and distance functions. Some of the main features in current systems are the support for managing different spatial reference and projection systems and support for applications like transportation systems, which require linear referencing capability.
References
- Chamberlin, D. (1997). Using the New Db2: IBM's Object Relational System. Morgan Kaufmann, San Fransisco, CA.
- Defazio, S. et al. (1995). Integrating IR and RDBMS Using Cooperative Indexing, Proceedings of SIGIR, Seattle, Washington.
- M.J. Egenhofer. (1993). What's Special About Spatial? Database requirements for Vehicle Navigation in Geographic space, ACM SIGMOD, 1993.
- K. Gardels. (1997). Open GIS and On-Line Environment Libraries. ACM SIGMOD Record, 26(1):32-38, March, 1997.
- R.H. Guting. (1994). An Introduction to Spatial Database Systems. VLDB, 3:357:399, 1994.
- W. Kim, J. Garza, and A. Kesin. (1993). Spatial data management in Database Systems. pages 1-13, 3rd Intl. Symposium on Advances in Spatial Databases, 1993.
- OGC. (1998). The Open GIS Consortium. http://www.opengis.com .
- Oracle8i Spatial Cartridge User's Guide and Reference, Release 8i, 1998.
- M. Stonebreaker and G. Kennitz. (1993). POSTGRES Next-Generation Database Management System. Communications of the ACM, 34(10):78-92, 1993.
- M. Stonebreaker and D. Moore. (1997). Object Relational DBMSs: The next great wave. Morgan Kaufmann, 1997.
- M. F. Worboys. (1995) GIS: A computing perspective. Taylor and Francis. 1995.
- Oracle Spatial White paper - http://www.oracle.com/database/options/spatial/