In virtually every organization, data are stored in a variety of ways
and managed by different database and file systems. Applications requi
ring data from multiple sources must recognize and deal with the speci
fics of each data source and must also perform any necessary data inte
gration. The objective of a multidatabase system is to provide applica
tion developers and end users with an integrated view of and a uniform
interface to all the required data. The view and the interface should
be independent of where the data are stored and how the data are mana
ged. CORDS is a research project focused on distributed applications.
As part of this project, we are designing and prototyping a multidatab
ase system. This paper provides an overview of the system architecture
and describes the approaches taken in the following areas: management
of catalog information, schema integration, global query optimization
, (distributed) transaction management, and interactions with componen
t data sources. The prototype system gives application developers a vi
ew of a single relational database system. Currently supported compone
nt data sources include several relational database systems, a hierarc
hical database system, and a network database system.