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DESIGN SPATIAL CACHE FOR WEBGIS 
LUO Yingwei *, WANG Xiaolin and XU Zhuoqun 
Dept. of Computer Science and Technology, Peking University, Beijing, P.R.China, 100871 — lyw@pku.edu.cn 
KEY WORDS: Component, WebGIS, Geo-Union, Spatial Cache Framework 
ABSTRACT: 
À spatial cache framework is designed and adopted in a component based WebGIS system Geo-Union to improve its performance in 
network environment. The spatial cache framework includes three typical cache modes: database cache, network cache and cache 
server (data proxy server). 
1. INTRODUCTION: GEO-UNION 
Geo-Union is a GIS platform developed by spatial information 
lab in dept. of computer science and technology, Peking 
University. Geo-Union has a multi-level Client/Server 
architecture, which is implemented by principle of ORDB and 
component techniques. Geo-Union provides an object-oriented, 
extensible GIS component library for further GIS application 
developers. Geo-Union can be used in both stand-alone 
environment and network environment. 
Component model is a primary approach to deepen the 
functions of WebGIS (Bin Li, 2001). To make the system more 
clear, Geo-Union can be divided into four layers: Geo-Union 
application layer, Geo-Union component layer, Geo-Union 
service layer and Geo-Union storage layer, where service layer 
has different units to provide both client services and server 
services. Figurel shows the architecture (Dept. of Computer 
Science and Technology, Peking University, 2002). 
Hierarchical spatial component object model can distribute GIS 
functions in network reasonably and make the system reusable, 
as well as provide efficiency approach for further development 
and integration with other Systems. 
Geo- Union 
  
Application Layer | A Geo-Union 
Th 7 Client 
Siete AT ENS 1 
- Geo- Union / AN B 
Component Las Layer CONCERN. NS 
; 1i Y fm Netw ork 
Geo-Union 
Service Layer 
NS: eu 
  
   
1 f —— 
Abu savent T | - Geo- Union 
Geo-Union | deu Server 
Storage Layer 
  
Figure 1 The Architecture of Geo-Union 
  
  
(1) Storage layer is the ground of Geo-Union. Storage layer is 
responsible for storage and management of both spatial data and 
non-spatial data based on ORDB. The main problems solved at 
this layer are how to represent and store spatial data, and how to 
maintain relationships among spatial data. 
(2) Service layer is in charge of spatial data access and process, 
which can be divided into another two parts: Geo-Union client 
provides data access and process services to component layer, 
  
* Corresponding author: LUO Yingwei, lyw@pku.edu.cn. 
201 
and Geo-Union server provides data access and process services 
to Geo-Union client through interacting with storage layer. 
Geo-Union server can manage different spatial data resources, 
and also can reply to different spatial data requests from 
different clients. Geo-Union client and Geo-Union server are 
two independent parts but have close relationship with each 
other. Geo-Union server provides the services of data access, 
spatial index, basic spatial query, transaction process, data share 
and so on. Geo-Union client provides different GIS tools and 
further development functions to component layer based on the 
services from Geo-Union server. Cache is an important unit of 
Geo-Union client, which is imported to reduce network load 
and improve response speed of the system. Using Geo-Union 
client, we can develop a simulation server, which can reduce 
network load and improve response speed through its cache. 
(3) Component layer provides a rich set of services 
(components) to develop domain-oriented GIS application 
systems for further developers. Component layer provides 
interface of GIS functions to users, but the implementation 
details are completed in service layer. Component layer exists 
as a component library, and servers as a bridge between users 
and service layer. Component layer provides function-explicit 
and reusable interface components for users according to the 
functions of service layer. 
(4) The work in application layer is to exploit application 
systems for different special domains by assembling and 
integrating Geo-Union components. These application systems 
can be running both in desktop and network environment. 
2. SPATIAL CACHE FOR GEO-UNION 
Cache is an important technique for improving the performance 
of system. In Geo-Union, there are two aspects affecting the 
efficiency of data access: one is the access to database, 
especially when storing spatial data in ORDB; the other is the 
transmission of spatial data in network. We take different 
spatial cache modes to solve these two problems in Geo-Union. 
2.1 Spatial Cache Framework 
Figure 2 is the spatial cache framework in Geo-Union. The 
spatial cache framework includes three es cache modes: 
database cache, network cache and cache server (data proxy 
server).