Large Number Of Information Sources Research Articles

An authorization model for a distributed hypertext system

Digital libraries support quick and efficient access to a large number of information sources that are distributed but interlinked. As the amount of information to be shared grows, the need to restrict access only to specific users or for specific usage will surely arise. The protection of information in digital libraries, however, is difficult because of the peculiarity of the hypertext paradigm which is generally used to represent information in digital libraries, together with the fact that related data in a hypertext are often distributed at different sites. We present an authorization model for distributed hypertext systems. Our model supports authorizations at different granularity levels, takes into consideration different types of data and the relationships among them, and allows administrative privileges to be delegated.

Data model and query evaluation in global information systems

Global information systems involve a large number of information sources distributed over computer networks. The variety of information sources and disparity of interfaces makes the task of easily locating and efficiently accessing information over the network very cumbersome. We describe an architecture for global information systems that is especially tailored to address the challenges raised in such an environment, and distinguish our architecture from architectures of multidatabase and distributed database systems. Our architecture is based on presenting a conceptually unified view of the information space to a user, specifying rich descriptions of the contents of the information sources, and using these descriptions for optimizing queries posed in the unified view. The contributions of this paper include: (1) we identify aspects of site descriptions that are useful in query optimization; (2) we describe query optimization techniques that minimize the number of information sources accessed; and (3) we demonstrate the need for interleaving planning and query execution in such a system, and present an algorithm for this purpose.