International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B2. Istanbul 2004 
  
  
and the Web Server. As depicted in Figure 1, the WAP 
Gateway consists of WML encoders and WMLScript decoders. 
The WAP Gateway can optimize the communication process 
and may offer mobile service enhancements, such as location, 
privacy, and presence based services. The WAP Gateway 
communicates with the client (WAP microbrowser) using the 
WAP protocols, and it communicates with the Web Server 
using the standard Internet protocols such as HTTP/HTTPS. 
Once the WAP Gateway receives WAP requests from the client, 
it translates the requests to HTTP requests, and then sends them 
to the Web Server. Once the WAP Gateway receives HTTP 
responses (web contents) from the Web Server, it translates the 
web contents to compact encoded binary formats for reducing 
the size and number of packets traveling over the wireless 
network to the client for displaying and/or processing. 
The Web Server includes a Web Container and Web protocols 
support, security support, and so on. Web caching mechanism 
for Geospatial Information The Web Container is responsible 
for managing a Java Servlet Engine and Java Server Pagers 
(JSP). An Internet GIS system based on Java often uses Java 
Applets and/or Servlets to extend the dynamically displaying 
functionality for the Web browser. This paper uses a Servlet 
Engine instead of running Applets and/or Servlets inside the 
Web Server, which has several advantages as follow: 
| The Servlet Engine runs itself inside the Web Server. But 
applets inside the Web Server must be dynamically downloaded 
to the client for processing, which would increase the load of 
wireless and mobile devices (Especially, a WAP phone has not 
the capability of running applets. ). 
2 The Servlet Engine can host Servlets and provide them 
with standard Java Servlet APIs. 
3 The Servlet Engine decouples Servlets processing from 
specific implementation details of the Web Server. This 
increases the flexibility of the system architecture, as it allows 
the Web Server to change without impacting on the overall 
system. The Servlet Engine can also provide various 
management features that help to shift the load of Servlets 
processing away from the Web Server. 
The client devices of WAP-based Mobile GIS have several 
types (e.g. PDA and WAP phone) whose displaying and 
presenting capabilities are different. So there must has a 
mechanism at the server side, that is, the Web Server may 
determine the type of the client device and generate 
corresponding presentation logic for the client. Fortunately, the 
Servlet Engine can solve the problem effectively. The Servlet 
Engine may provide two kinds of Servlets: the one is presenting 
Servlet which is responsible for generating corresponding 
presentation logic according to the type of the client device for 
the client; the orther is identifying Servlet which is responsible 
for determining the type of the client device (through the only 
ID of the client device accessing mobile networks) and then 
notify presenting Servlet. 
The Servlet Engine is responsible for manage Servlets and 
provide support for JSP. Since Servlets run inside the Web 
Server, everyone does not need a GUI. Servlets in the same 
servlet engine can share resources and chain together. So the 
Web Server can generate dynamical Web contents by running 
Servlets (i.e. presenting Servlets) to response for client requests 
like CGI. And Servlets are more efficient than the CGI 
approach and the Fast-CGl approach. Through Servlets and/or 
JSP, the client side may indirectly perform EJB components 
inside the Application Server to implement GIS business logic, 
716 
such as spatial analysis, spatial and attribute querying, route 
planning, geocoding and gazetteer, and so on. 
4.3 Application Tier 
Application tier is the core of the architecture. It corresponds 
GIS Application Servers that communicate with the Web Server 
in WAP service tier through Remote Mcthod Invocation (RMI). 
An EIB container at an Application Server is the runtime 
environment of EJB components including GIS Session Beans 
and GIS Entity Beans, and controls these components to be 
performed and transferred. At the same time, the container also 
provides these components with all required services for 
distributed computing environments. Thus, these EJB 
components could more efficiently execute in the Application 
Server. The EJB components can use JDBC (Java Database 
Connection) technology to access to database servers, and use 
JMS (Java Message Service) technology to connect to back-end 
legacy systems. The Application Server has a special Locating 
Entity Bean to communicate the Mobile Position Centre (MPC), 
a Server providing geographic location information, with 
Mobile Location Protocol (MLP) (Location Interoperability 
Forum, 2002). The mobile position technologies for real-time 
capturing the location information of mobile users generally are 
GPS, Cell Of Origin (COO), Time Of Arrival (TOA), Angle Of 
Arrival (AOA), Enhanced Observed Time Difference (E-OTD) 
and so on. 
4.4 Data Service Tier 
Data service tier corresponds Database Servers that are used to 
manage and store geospatial and attribute data of the whole 
system. Object oriented database management system 
(OODBMS) is the most desired database server for a GIS 
system, but OODBMS is immature and very costly currently, so 
it is not popular and to be used commonly (Gong Jianya, 2001). 
At present, the mainstream solution is that large object-relation 
database systems such as DB2, Oracle, Sybase, SQL Server, 
and so on are used to manage and store GIS data, at the same 
time, spatial data engine (SDE) also can be developed to build 
the communication between data service tier and application 
tier. SDE is an open standards-based middleware such as 
ArcSDE, Spatial Ware and Oracle Spatial. 
S. JZ2EE-BASED PROTOTYPE SYSTEM 
Using the 100% Pure Java J2EE solution, the above architecture 
is open and cross-platform, and has the characteristics such as 
extensibility, stability and reliability, which could satisfy 
system requirements of WAP-based Mobile GIS. Based on the 
architecture, a prototype system of WAP-based Mobile GIS has 
been developed. In the prototype system, the server side uses 
Apache Tomcat 5 as the web server, BEA WebLogic 8.1 as the 
application server, Oracle 8i and ESRI ArcSDE as the database 
server, and it provides a range of basic GIS functions (e.g. 
spatial and attribute querying, route planning, geocoding, 
mapping, etc.) to a Mobile GIS user using the Servlet Engine 
and EJB components to gain and process spatial geometry 
object in back-end spatial databases. The client side uses WAP 
phone with a WAP microbrowser and may obtain maps in 
WBMP format from the server side, and it has the basic map 
browsing functions such as zooming out, zooming in, moving 
(up, down, left and right). The running results are showed in 
Figure 2. 
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REFEREN 
Li Deren, I 
Technique 
Communic: 
University, 
Shi Wenzh 
of Mobile 
Mobile and