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The Client-Server Architecture of Delta-X
Jan Medved
Natural Resources Canada, 615 Booth Street, Ottawa, Ontario, KIA 0A9
Juraj Petras
Interobjects Spatial Research, P. O. Box 5836, Ottawa, Ontario, K2E 6K2
Abstract
Delta-X is a federated multidatabase system that provides inter-operability between different database man-
agement systems (DBMS). It is based on the assumption that each underlying DBMS is based on the client-
server architecture and each client workstation is connected to a network that is configured with access to at
least one DBMS server. A client, besides being able to query and access a server database, is typically config-
ured as a geographic Information System’s workstation. This paper describes the separate functionalities of a
client and a server, and the mode of interconnection and inter-operability between them. We describe the
architecture, configuration requirements, services offered by servers and client-server and server-server com-
munication within the Delta-X system.
Keywords
Distributed databases, inter-operability, transaction processing systems, client-server architectures, GIS.
1.0 Introduction
The deployment of large local and wide area net-
works (LANs and WANS) that connect thousands of
client and server nodes together with the availability
of a great variety of software packages that store and
manipulate data (in our case, geomatic data) will
soon cause software interoperability and data com-
patibility problems. Different people and depart-
ments within large organizations, which often use
different (and incompatible) GIS systems and store
their geomatic data in different locations, need to
share their data with each other. Also, organizations
need to share data with other organizations.
Apart from the software and data compatibility
problems, sharing of geographically distributed data
poses multiple organizational problems, such as how
to advertise the availability of data to the user com-
munity, or how to store data for best availability and/
or transfer performance.
To address the above issues, we designed and imple-
mented Delta-X, a system that connects over a LAN
or WAN a heterogeneous network of databases serv-
ers to various GIS clients. A GIS client can be a
workstation running any commercially available
GIS system, such as CARIS [6] or ARC/INFO [5].
Delta-X creates a platform for a seamless exchange
of geomatic data between different systems on dif-
ferent locations. Delta-X enables uniform integrated
access to data from different geographic information
systems. A GIS can export data to Delta-X or import
data from Delta-X in many different formats, such
as CCOGIF, SIF, ARC/INFO, or CARIS. Our cur-
rent implementation of Delta-X stores different
types of geomatic data - spatial data (vector or ras-
ter), spatial data attributes, structured text, and oth-
ers. This can be easily modified to store other types
of spatial and non-spatial data.
From a user's perspective, Delta-X is a distributed
billboard through which users can exchange data.
Data enters Delta-X in one format on one location,
and the same data exits Delta-X in a different format
on a different location. Note also, that although the
Delta-X prototype works with GIS data, its architec-
ture, design, and implementation can be applied to
any type of data. In a sense, GIS data constitutes a
very difficult case among applications that can use
the Delta-X paradigm because of large volumes of
data that need to be stored, converted, and trans-
ferred within a network, and because of a large vari-
ety of formats that the data can be presented in.
The underlying paradigm of Delta-X is that of a dis-
tributed database. Data in Delta-X is stored on mul-
tiple servers distributed across a LAN or WAN. The
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