A new architecture for cyber maps: An internet-oriented next-generation spatial information service System
This active retrieval mechanism can be adapted to meet the demand for wireless nomadic
database retrieval by adding process management of database transactions and by buffering the
intermediate results,
Prototype implementation and performance evaluation
We implemented a prototype (nicknamed Cyber Map) of our proposed new architecture for NSIS
and evaluated its performance.
Overview of Cyber Map Architecture
The system architecture of Cyber Map is based on the third-generation information service
system architecture, as shown in Table 1. Basically, it consists of a method of connecting WWW
servers with the ORDBMS. For this ORDBMS, we selected Illustra (which was purchased by
Informix Softswm, Inc. in 1996) which progressively adopts SQL3 as the database retrieval
language, and provides a “data blade” that can easily extend retrieval functions. Using Illustr~
we achieved unified management of spatial and attribute databases. And using the web data
blade, we made an active retrieval mechanism that can supply information to each web terminal
in the most suitable format by linking the WWW server and Illustra and by locating the media
processing function in the data blade.
Details of Active Retrieval Mechanism
After the terminal capabilities (TID), which express display resolution and graphics processing
speed of each web terminal together with the retrieval conditions, have been transferred to the
WWW server, the retrieval mechanism provides information by applying the most suitable media
processing, In particular, for high-resolution terminals, we created a function that provides a 3-
dimensional virtual space in VRML format using 2-dimensional geographical map together with
the number of floors, which substitutes for height information. Details of the implementation of
the active retrieval mechanism, are given below.
(1) Web interface function (Web data blade)
The web data blade is equipped with the dynamic HTML generation function “WebExplodeo”.
In Cyber Map, we utilize this function to dynamically generate and execute the spatial retrieval
structural query language as “SR-SQL”. The process up to getting the SR-SQL suitable for the
terminal’s capabilities is explained below.
[step#l] When it gets a ~trieval function from a web terminal, Web Explode gets a template for
generating SR-SQL suitable for the retrieval type.
[step##l] After getting this template, Web Explode generates SR-SQL based on the transfer
function obtained from the terminal capability table and the retrieval parameters supported from
the web terminal. If it receives a retrieval request from a web terminal with a display resolution
of 1152x864, for example, then VRML transfer will be selected.
[step#3] Parameters of the retrieval form, which is assigned from the web terminal, are inserted
into variables of a where phrase and they generate SR-SQL.
(2) Spatial retrieval fimctions
The two-dimensional data blade supports spatial retrieval functions based on R-Tree spatial
indexing theory[Gut 84]. In Cyber Map, spatial retrieval functions such as retrievals in a circular
area around a specified spatial location (circular retrieval) are described in a template position in
a table storing SR-SQL, and they are used by substituting variables in the SR-SQL production
part of the web data blade. For example, in order to execute a circular retrieval centered on a
position (25, 50) in the Shinjuku area and within a 100-meter radius, spatial retrieval is done by
generating the following SR-SQL.
select transfer function(tuples)
from figure table of Shinjukuarea
where Intersectsln (Circ (25, 50, 100), tuples);
(3) VRML generating functions
There is a mechanism for generating a virtual 3-dimensional space from a 2-dimensional space
plus height attributes. As already mentioned, we took a method that calls a function by SR-SQL
which can generate one object from one tuple stored in a 2dimensional figm table, in order to
generate VRML. For this VRML generating function, we produced “vrml-funco” which can
generate a 3-dimensional object from Poly & Path typed datA which describes closed polygon
line figures and the number of floors in a building. This function is described in SR-SQL selected
from the terminal capability table, and is executed after spatial retrieval.
Performance Evaluation
To evaluate the performance of Cyber Map, we used a residential map CD-ROM (Zmap-Town II
’95, Tarna district Vol. 1.1) published by Zenrin Co., Ltd.. We produced a function that could
generate a virtual 3-dimensional space as VRML using this database. An example of the display
Fig. 3 Display exmaple of generated 3-dimensionalvirtual space by the active retrieval mechanism
Fig 4 Relation between generated VRML capacity and processingtime
of this function is shown in Fig. 3. The left window is an example of a GIF-type image map
(Kokubunji-city area 600x600 m) on NetSpace Navigator. When the demanded position for
retrieval is specified on this image map by setting the radius at the bottom of this window, the
system mt.rieves buildings and roads within the circular area defined by that radius and displays
them as a 3-dimensional virtual space. The right window in Fig. 3 shows a Web Space (VRML
browser from Silicon Graphics, Inc.) display of VRML generated when the radius was set to 100
m. The response time measured from the demand for circular retrieval to the display of the virtual
3-dimensional space using an Indigo2 (Silicon Graphics Inc.’s graphics workstation) is shown in
Fig. 4. The average response time for circular retrieval within a 150-m radius was 10 seconds,
indicating that Cyber Map has good enough performance for practical use.
Conclusion
The new architecture we propose provides unified management of spatial data and attribute data
and an active retrieval mechanism for an internet-oriented next-generation spatial information
service system. It offers a clear approach to making mobile and interoperable information service
systems. A prototype implementation, called Cyber Map, demonstrated good enough
performance for practical use. The interactive link between the web terminal and the supplied
spatial information remains as a topic of future study.
References
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