We propose an architecture designed to support interoperability between autonomous heterogeneous databases. The architecture supports a distributed information discovery process and avoids the use of integrated schemas and centralised structures containing information about the shared data. Users of a database can access its local data as well as data from other databases in the system. Such access can be supported without violating the privacy and confidentiality of the data, and preserving the autonomy of the databases. With the proposed architecture it is possible to support change by adding and removing databases from the system. 1 Introduction The development of database management systems has increased the utility of such systems, but has not solved the problem of having a great number of separate databases in a large company or community. Users would like to access and manipulate data from several databases, and applications may require data from a wide variety of inde...

this paper we demonstrate, through a case study, the use of the approach proposed in previous work [18, 20, 21, 22]. The approach permits distributed information discovery when interoperating with various hospital databases. Our aim is to allow "naive" users (doctors, nurses, fellows, members of the hospital staff) to access and manipulate local and remote data. The approach is an alternative to the problem of building an integrated global schema when dealing with a large number of databases. The idea is to perform the complete execution of a query: data request, database location and data access, in a distributed way, avoiding the use of integrated schemas, centralised structures and broadcast to all the databases in the system. The approach attempts to preserve the autonomy of the hospital databases and supports evolution of the system in terms of adding or removing databases.

In this technical report we discuss a methodology and a support tool to assist the coordinator of a federation with the construction and evolution of hierarchical information structures. The definition of the terms composing the hierarchical information structures is based on the interests of the users and the applications, and the information that each database system shares with the other components. Therefore, the different group names refer to the types of databases participating in the federation. The other levels are related to the entity names, attribute names, class names, object names, and instances of the databases. The methodology consists of constructing a hierarchical information structure by incremental addition of the participating database systems. The support tool assists with the automation of some steps during construction and evolution of the structures.

Introduction An important issue when dealing with interoperability of heterogeneous databases is information discovery. This is the location and identification of information that is relevant, identical, similar or related to the requested data of a query. As outlined by Sheth [7], in the future, the primary issue will not be to efficiently process the data that is known to be relevant, but to determine which data is relevant and where it is located. Some approaches have been proposed in the literature addressing the information discovery problem for a large number of databases. One approach [1, 8] is the use of an external indexing scheme. However, the autonomy of the involved databases is not strictly respected, since they have to provide both the content and the structure to other databases. It is not specified how the external indexes are updated when components are added and removed from the system. For simplicity, it is assumed that all the data is publi