International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B4. Istanbul 2004 
  
  
mobile equipments, i.e., PDA, laptop, and mobile phones etc. 
should be comprised with mobile databases and mobile 
computing environment. Wireless GIS server is the main part of 
WGIS, it deals with all kinds of processing in wireless transfers, 
including ‘read’, ‘write’, ‘delete’, ‘update’ and ‘commit’ etc. 
As the wireless communication is considered the factors, for 
example, communication cost, communication time, power 
supply etc., so the wireless server should take into account the 
problems mentioned above and provides an optimal search for 
wireless users. GIS spatial database (DB) is used to manage all 
types of massive GIS data, while convention DBMS could fit 
the function. Between the GIS DB and wireless server, a spatial 
database engine, which could be ODBC or SDE, should be 
produced in order to provide services for users. 
The wireless GIS is the management and application system of 
functional and wireless Geo-spatial data. In this system, we can 
realize tremendous Geo-spatial data storage and management in 
GIS, fast queries of multi-dimensional spatial data and search in 
wireless network, wireless station over switch, wireless 
vendor’s authentication and management, encrypted wireless 
data transferring etc. 
Being compared with the conventional LAN, the wireless 
network technology is possessed itself overwhelming 
predominance, however, wireless couldn't be absolutely 
replaced by the wired environment and is used to make up the 
restrictions of wired, with it purpose of the extension of the 
wired. The Geo-science are now facing a shift in the way for 
GIS development in human works and human access of works, 
so the question becomes how to give GIS clients accessing any 
types of Geo-Information quickly, securely, at anytime and in 
anywhere. 
The development of Wireless GIS is served the first and top 
priority to the development of the mobile computing 
technology. Mobile computing technology is a revolutionary 
technology, born as a result of the remarkable advance in the 
development of computer hardware and wireless 
communication. It enables us to access information at anytime 
and in anywhere even in the absence of physical network 
connection. It is essential in a mobile computing environment 
to serve mobile clients to access remote information at anytime 
and at any places. In the process of assessing files on remote 
servers by the clients, requests are sent by them to mobile 
support stations in where the files are thus received from the 
remote servers and then are delivered back to the clients. The 
high mobility of mobiles for mobile hosts and the narrow 
bandwidth in the wireless network may cause certain delay in 
accessing files. Also, because mobile clients may request the 
services of assessing file too often and givc rise to bandwidth 
contention among them, latencies can be caused on the whole. 
The important characteristics in wireless GIS transfer and 
storage are needed to be considered are as follows: 
(1) The environment, in where wireless GIS is deployed, is the 
mixture of two different networks, the fixed and the wireless 
networks. The fixed network is characterized by the fixed 
hosting location, relatively high capacity, high reliability and 
low connection cost. In contrast, the wireless network is to 
support dynamic network topology but with relatively low 
capacity, low reliability and high connection cost. In order to 
avoid compromising database performance due to the use of the 
306 
wireless network, recently some techniques have been proposed, 
including: 
e Reducing the number of data exchanged via mobile network; 
e Reducing the response time of accessing data via mobile 
network; 
e Providing data cache on mobile host; 
(2) The resources available to mobile users are generally very 
limited. As a result, mobile hosts will tend to be highly 
personalized. From the data management's point of view, 
mobile users will likely and solely bring the fraction of data 
they need to access frequently in mobiles. A new challenge 
arises for coping with the requirement of consistency on 
databases (both on mobile and fixed hosts) especially when 
those fractions are not completely independent to each other. 
Actually many techniques have already been proposed to 
address this problem, including: 
e Transaction management for wireless transfer; 
e Allocation of mobile database replication (materialized view) 
on the fixed network; 
(3) In general, wireless communications are consisted of low 
security. The worst case is, for example, that our data on the 
mobile hosts would be completely lost if the mobile hosts 
become the subjects of thieves. 
The consequence of the above characteristics is concluded that 
wireless GIS, in general, contains a high degree of 
unavailability. It is not to say that most data management issues 
in mobile information systems are related, directly or indirectly, 
to the problem of low data availability; thus, data availability is 
the central issue in transferring mobile spatial data. 
Accordingly, addressing the problem of low data transferring 
speed and management would have significant contribution in 
the establishment of wireless GIS technology. 
3. DISTRIBUTED DATA TRANSFERRING 
STRATEGIES 
Wireless GIS impulses  Geo-science and X wireless 
communication technique to a new era through enlarging the 
network's carrying capacity and application domain. Nowadays, 
since the application of wired network is gradually saturated, 
the wireless application has become wider and wider. 
Meanwhile WGIS provides some newly hot spot applicable 
strategy. 
The data is the most unvigorous segment in GIS, whereas 
spatial data, which is related to GIS, is multi-original and 
complicated, in terms of data types and formats, i.e., gigantic 
grid image data, spatial vector data, metadata, etc. lt is an 
essential matter in WGIS operation for constructing geographic 
entity objects, organizing and transferring spatial data, and 
realizing data share in the Internet. Integrating the character of 
wireless transferring, WGIS spatial data transferring strategy 
should be considered the following facts: 
(1) Unrestricted by time and location. It is also the 
predominance for wireless network to realize WGIS from 
preventing disturbances from outside conditional environment 
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