A
BSTRACT
The introduction of faster and cheaper global data networks has resulted in a
significant growth in demand for integrated access to new and existing information
sources. A Global Information System allows integrated access to any number of
such information sources independent of the degree of heterogeneity of the
associated subsystems. However, Global Information Systems do place
integration demands on these subsystems in that they require them, for example,
to be able to cooperate even if not designed for this purpose.
Previous approaches for database integration such as those adopted for
distributed, federated and multi-database systems are not feasible for Global
Information Systems. These approaches assume the subsystems to be database
management systems and, further, expect that they conform to some form of global
goal in order to be integrated. They do not scale up to such large, evolving
networks with high-levels of heterogeneity in terms of the essential nature of the
information sources.
This thesis presents a different approach based on the integration of subsystems
by means of gateways. A gateway is a program which allows global access to
data stored in a subsystem without requiring changes to that subsystem. The
subsystem continues to operate normally and remains responsible for updates to
local data while the gateways enable data to be retrieved by any users and
applications of the global network.
We introduce a graphical language, SGIS, for describing the general architecture,
configurations and components of Global Information Systems. The language
SGIS supports the description of both the structure and dynamic interactions of
such systems.
