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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B2. Istanbul 2004
Figure 1. Wireless GIS Architecture
Every user request, invokes an instance of database
corresponding to the desired function on data. Server
application extracts the geo-data corresponding to the request
from main database, converts the response to XML format and
sends it back to the client (Figure 2) (Takino Shuichi, 2001).
Server
Geometry Attribute
ibis ELI"
Client
Figure 2. GIS Data Model
3. WIRELESS SPATIAL DATABASE: XML
Based on assessing different file formats, XML has been found
as one of the most optimal variants for the GIS applications. It
is optimal to provide to the user a rich set of functions and to
use the wireless network minimally. XML posses the following
features:
. Interpretation in a wide range of mobile devices;
. Alternative ways for information representation
(text, voice);
. Expandability;
. Structure flexibility.
XML-technology meets the requirements for the format
development. The logical structure of the XML-based language
is easy [for ‘program processing «XML — 10, . W3C
Recommendation, 1998). Software can interpret the content of
an XML file in a more appropriate way for each device or easy
conversion of the contents to any intermediate format. XML is
already widely used in the Internet. Therefore, a new Mark-up
Language could be easily integrated in current WW W(World
Wide web) services (Garmash, Artem, 2001).
XML is a universal format for describing any data. When XML
is discussed as a meta-language, it means that in real world,
computer systems and databases contain data in incompatible
formats. One of the most time consuming challenges for
developers has been to exchange data between such systems
over the Internet. Converting the data to XML can greatly
reduce this complexity and create data that can be read by
different types of applications, and this leads to a platform-
independent structure.
XML supplies structure to documents. Structure by itself
imposes constraints. Even though, the structure may seem like a
limitation that might prevent flexibility, in reality it encourages
interoperability and lays a common framework for tools and
other utilities to evolve (Bell J., Loton T., Allamaraju S., Dalton
S., Brown S., Harbourne-Thomas A., Holm B., Kunnumpurath
M. M.. Li S. 2002).
Regarding to wireless environment and device limitations,
XML provides a suitable data format to respond to the demands
of the application developed for wireless environment.
4. IMPLEMENTATION PHASE
The application developed in this paper, uses a pocket PC as a
client. device. The pocket PC is equipped with a Java
application; also it uses GSM (Global System for Mobile
Communication) wireless modem and SIM (Subscriber Identity
Module) as wireless modem.
Residing the application and functions on the client side move
the burden of the system to the client, and client needs no more
transaction with the server until invocation of another data or
service, and this generates the thick client architecture. The
execution of the application generates an interface for choosing
the map (Figure 3).
Figure 3. Execution of Application on Device Generates an
Interface to Request the Map
Choosing the map option, sends a URL to the server side, the
URL consists of the server's IP (Internet Provider), and the
server-side application address.
The sent URL invokes the geo-data from the server, retrieves
the interested geo-data and converts it to an XML document
(Figure 4), and client-side application invokes the traverse
function to parse the XML document.
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