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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B2. Istanbul 2004
system functions and more application: fields than the former.
Morcover, it can work on a wide range of mobile devices with a
WAP microbrowser only, from Personal Digital Assistants
(PDAs), mobile phones, and in-car computers to other small
mobile devices, and keeps the standard browsing style. WAP-
based Mobile GIS can be described as mobile users (with a
WAP mobile terminal only) can perform the almost’ same
functionality as of Internet GIS but in a mobile environment at
any time, any place and without the limitation of operating
system and wired link. Altogether, it is because of the
advantages of WAP that we believe WAP-based Mobile GIS
will play a leading role in our mobile information services
markets.
The framework and soul of a distributed system is the system
architecture deciding the distribution of system functions and
data. WAP-based Mobile GIS, as a new development to Internet
GIS, is still in a preliminary stage, whose research issues need
be deal with. However, the architecture solution to WAP-based
Mobile “GIS is the key and core of its whole researches.
Although Li Deren, et al (2002) and Li Luqun, et al (2002) üsed
to present an architecture for Mobile GIS respectively, the
architectures were conceptual ones and had difficulty playing a
substantially directive role to building a Mobile GIS system, let
alone WAP-based Mobile GIS.
3. ARCHITECTURE SOLUTIONS
WAP-based Mobile GIS is a “thin client” distributed system via
mobile Internet. It must be an open.’ extendable, stable and
cross-platform distributed system, because of the increasing
application demands and the diversity of mobile terminals.
Currently, popular system architecture solutions for distributed
systems are all based on distributed object technologies. There
are three mainstream industry standards: Microsoft's Windows
Distributed Network Architecture (Windows DNA)/ NET
Architecture, Object Management Group's Common Object
Request Broker Architecture (CORBA), Sun's Java 2 Enterprise
Edition (J2EE) Architecture. A system based on Windows
DNA/NET Architecture solution can only use Microsoft's
platforms from development, deployment to running, including
developing platforms and operating system. It can not cross
operating system platform especially, which is the fatal
weakness ‘of Windows DNA/NET Architecture. CORBA is too
huge and complicated. And its technologies and standards are
updated relatively slowly. J2EE is a specification and standard
created by Sun and her industry partners, and it evolves quickly.
J2EE provides support for thé technologies such as Enterprise
JavaBeans (EJB), Java Servlets API and Java Server Pagers
(JSP), and so on. J2EE solution reduces the cost and complexity
of developing a multi-tier distributed system which can be
rapidly developed and deployed, and can enhance the
portability, security, load balancing and extensibility of "a
distributed system. There are the following advantages to build
distributed GIS based on J2EE (Mao Haifeng, 2004): (1) cross-
platform; (2) multi-tier séparating to complicated tasks: (3)
component reusing and (4) module developing. Thus, J2EE
solution can satisfy the system requirements of WAP-based
Mobile GIS. Based on J2EE, this paper proposes a distributed
architecturé for WAP-based Mobile GIS.
4. A DISTRIBUTED ARCHITECTURE
As showed on Figure 1, the J2EE-based distributed architecture
is composed of four logic tiers from the client side to the server
side: presentation tier,. WAP service’ tier, application tier and
data service tier. At the fat server side, Geospatial information
Web. caching mechanism is used to optimize the performance
capability and reducing the access delay of the client. Functions
and components of each logic tier and the statement about the
distribution of presentation logic, business logic and geospatial
data in the architecture are detailedly stated as follow.
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Figure 1: A distributed architecture of WAP-based Mobile GIS
4.1. Presentation Tier
Presentation tier is a carrier of the client of WAP-based Mobile
GIS, and is mainly. responsible for, implementing the
presentation logic of GIS data. Generally, the client without
local-storage data is a WAP microbrowser that controls the GUI
and is. analogous, to. a, standard. Web browser. The WAP
microbrowser needn’t perform any GIS business logic, don’t
directly connect to a back-end database server, and don’t store
itself state information, so it is a really “Thin Client”. The client
also may be a J2ME (Java 2 Micro Edition) application.
42. WAP Service Tier
WAP service tier includes a WAP Proxy (often referred to as à
WAP Gateway),and a Web Server. The WAP Gateway was
required to handle the protocol interworking between the client
