Location based services model for crime control
The users, both police and citizens, connect to the system by PDA, mobile phone, PC, etc. The system will check for the authentication and authorization [5] to identify the source of a message. Based on the security policy of the system, the authentication process can deny or allow the user to access the system. The authorization process is used to control access to resources once identity has been verified. Then the data will be obtained by data analysis and converted to longitude and latitude and sent to the database. The database consists of crime data and GIS data which will be integrated before sending to the server. The HTTP server/Map server/WAP server will do the computation. The Web browser/WAP browser is used for viewing the results.

Figure 2 Location Based Services Model for Crime Control
Privacy issue
Privacy is an important issue in a public information system. The location of a person may be a piece of sensitive information, especially when this is clearly identified with a time. Therefore, mechanisms must be devised to ensure privacy protection. Also, sufficient information must be available to the system to answer queries. The solution to this problem is the anonymous person policy. The system preserves information about each person but removes the identification of the person. This anonymous information can then be extracted to generate the aggregated information. The person identifications are only kept during the query computation and destroyed immediately afterwards, leaving only enough information for crime statistical purposes. However, this privacy policy is only applied to cases not involved with crime events; for example finding the nearest police station or hospital, or how to get from one place to another, etc. In the cases involving crime, it would be important to keep the person identifications for crime analysis purposes but this information should only be available to authorized personnel for investigative purposes.

System Development
We have developed the crime control system by integrating Minnesota MapServer, Internet server and crime database into a Web based client/server environment. The MapServer [6] is a system for developing web-based GIS applications. The core of the system is a Common Gateway Interface (CGI) application that allows developers to rapidly build and deploy web applications based on GIS databases using simple text-based configuration and presentation templates.

The PostgreSQL [7] database server has been used to manage the attribute data and multi-media content. PostgreSQL is an Object-Relational DBMS, supporting almost all SQL constructs, including sub-selects, transactions, and user-defined types and functions. The database consists of tables that hold all the attribute data and spatial data. The PostGIS adds support for geographic objects to the PostgreSQL object-relational database. In effect, PostGIS “spatially enables” the PostgreSQL server, allowing it to be used as a backend spatial database for geographic information systems (GIS). Real-time update of authorized users is also made possible. An authentication and authorization mechanism to check which users can be allowed to enter new data or update the existing database is also provided.

The users can access the system by web interface (PHP) that enables online access to the GIS layers and attribute information.

Figure 3 Components and Information Flow
Conclusion
In this paper we presented the requirements of a crime control system that is derived from users demands. We illustrated a model of location based services for crime control. We also described the features of the system that we are employing to guarantee user privacy and security. Most of the research presented in this paper is still a work in progress. We are currently implementing our model. In the near future, we hope to access the performance of our model on a very large group of user who are behaving in a very realistic manner.

References

1. World Bank's e-government website (2001). A Definition of E*Government. http://www1.worldbank.org.
2. Woods, P. (2001). e-Policing. http://www.e-policingreport.com.
3. Prasad, Maneesh (2002). Location based Services. http://www.GISdevelopment.net.
4. Kulak, Daryl, Guiney, Eamonn (1998). Use Cases Requirements in Context. Addison-Wesley, New York.
5. Garfinkel, Simson, Spafford, Gene (1997). Web Security & Commerce. O’ Reilly & Associates, U.S.A.
6. MapServer. Mapserver home page. http://mapserver.gis.umn.edu/
7. Raghavan V., Santitamnont P., Masumoto S., Honda K. (2002). Implementing Web GIS Applications using Open Source Software. http://www.GISdevelopment.net.