FEDERATED MULTI-DATABASE INFRASTRUCTURE 
FOR GIS INTEROPERABILITY - THE DELTA-X PROJECT 
Mosaad Allam 
Cherian Chaly 
Geomatics Canada 
615 Booth Street, Ottawa, Ontario, Canada K1A OE9 
Ekow Otoo 
Interobject Spatial Research Inc. 
Ottawa, Ontario, Canada 
ISPRS Commission II, Working Group 3 
KEY WORDS: Interoperability, Data-Federation, Metadata, Spatial-Browser, Client-Server, Infrastructure. 
ABSTRACT 
Access to a federated set of dispersed spatial databases over a wide area network is a major issue. Considering that there can be 
a variety of GISs and DBMSs residing on a heterogeneous array of platforms, this precipitates problems of data transfer from 
system to system. From the users point of view, the data should be current, available in readily usable format, easily accessible, 
supported with database management functionalities and allow selective feature retrievals. The user should have the option to 
use whatever database or GIS which is appropriate for the application. 
Delta-X, a code name for a federated spatial information management system, is an approach to providing interoperability in a 
network of heterogeneous databases. It establishes interoperability between different relational DBMS's, simple files and object 
repositories. Data is made accessible to users through a distributed virtual global schema definition. By this means, the 
independence and autonomy of control, of the individual datasets registered in the federation, are still respected, while still 
maintaining some integrated uniform access with respect to a particular GIS environment. 
To assist the users 1n identifying the source of data required for their applications, the MetaView/GIS spatial browser was 
developed. MetaView/GIS provides access to metadata of various databases. The Delta-X and MetaView provide a unique 
technology for the development of a Canadian spatial datainfrastructure. 
1. INTRODUCTION GIS software based system, and our efforts to retrieve data 
from various databases residing in other LANs in the Sector 
Geomatics Canada Mandate is to provide accurate and quickly revealed a number of operational problems, such as: 
current spatially georeferenced information about Canadian 
landmass. The Geographic Information Systems and e the transfer of data between a number “n” of GISs 
Services, a Division of Geomatics Canada, was set-up in 
1987 to develop applications to promote the use of the 
Department data, and to explore research that will aid in the 
growth of GIS technology. Initially, our main concern was to 
improve access to GIS data through improved 
communications facilities, and developing the technology 
required for building a spatial information infrastructure in 
the Sector to facilitate the ordering and distribution of GIS 
data. 
2 : 
requires “n?” conversion packages, 
e the different GIS have underlying database 
management systems (DBMS) that are based on 
different data models: relational, network, and 
object-oriented, 
e the data required by GIS applications resides in 
several database in different data types: vector, 
raster, structured text, free text, and knowledge 
base, 
e the available data is generally not in the format 
required by the GIS, and some processing and 
restructuring are required before it can be 
incorporated into the GIS application environment, 
e checking data out of the server and restructuring it 
into its local GIS data storage is cumbersome, 
e checking the data back onto the server, either as a 
new version or as an updated and revised form of 
an existing one posed more problems for database 
In 1988, the Division established the National GIS 
Technology Centre and acquired several GISs from several 
vendors. The GIS software was installed on personal 
computers (PCs) and UNIX workstations. The various 
systems were interconnected into an ethernet local area 
network (LAN). The heterogeneous GIS environment was 
selected due to the wide variety of GIS software and 
hardware platforms available on the market, and to simulate 
conditions in large organizations, where different GISs are 
used to store their spatial data in different databases. administrator, ; : 
e GIS databases available in agencies and 
The operation of the GISs in this simple LAN, in which a institutions that are geographically dispersed 
number of workstations (nodes), each runs a different vendor 
1 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B2. Vienna 1996