3. Support for parallelism and load-balancing 
within the cluster and across the whole Delta-X 
federation. 
4. The latest consistent state of the Delta-X feder- 
ated database will be preserved, based on the 
automatic incremental back-ups. 
5. Delta-X will support collection of data about who 
accessed which data and when, to support billing 
for access to data. 
6. Delta-X servers will support Simple Network 
Management Protocol (SNMP). An SNMP agent 
and a vendor-specific SNMP Management Infor- 
mation Base (MIB) will be developed, which will 
serve mainly for observation of the Delta-X fed- 
eration. The MIB will, for example, contain data 
about the current topology of the Delta-X federa- 
tion, the communication links to other servers, 
about completed and in-progress conversions, 
software error alarms (e.g. when a conversion 
routine crashes), data error alarms (e.g. when a 
conversion routine encounters a data inconsis- 
tency), billing data, etc. 
7.0 Conclusion 
The paper describes a flexible and powerful client/ 
server architecture which is targeted for two groups 
of users: distributors of geographical data and their 
customers (users). The distributors get a powerful 
automated data distribution system. Their customers 
can electronically download data in a format that is 
most suitable for them. The Delta-X architecture is 
flexible, and can be easily extended to support other 
types of applications. 
Acknowledgments 
We would like to thank Ekow Otoo for his inspiring 
ideas and comments which he always willing to 
share. We are also thankful to GIS Division, Energy 
and Mining Resources Canada for financial support 
of this project and last but not least the thoughts of 
gratitude lead to our wives Ivana and Maria for their 
understanding for our work. 
362 
References 
1. 
Ekow Otoo: A Federated spatial Information Sys- 
tem: Delta-X, 6^ Canadian Conference on GIS, 
Ottawa, Ontario, 1994 
. Cherian Chaly, Wenjing Zhu, Samuel Effah: 
MetaView: A GIS Spatial Browser - Functions 
and Services, 6‘ Canadian Conference on GIS, 
Ottawa, Ontario, 1994 
. Jim Gray, Andreas Reuter: Transaction Process- 
ing: Concepts and Techniques, Morgan Kauf- 
mann Publishers, San Mateo, California, 1993 
Bernard H. Boar: Implementing Client/Server 
Computing A Strategic Perspective. McGraw 
Hill, New York 1993 
ARCIINFO User's Guide. Environmental Sys- 
tem Research Institute, Redlands, California, 
1989 
. CARIS Command Reference. Universal Systems, 
Fredericton, New Brunswick, 1992 
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