Digital Object Abstraction Layer: A Middleware for Building Federated Digital Libraries

Federated digital libraries focus on the development of common services over multiple, heterogeneous digital repositories. To offer advanced services for federated digital libraries, there is a need to provide an abstract representation of digital objects stored within a specific repository, maintaining their semantics. In this paper a middleware for the development of federated digital libraries is introduced, named Digital Object Abstraction Layer (DOAL). It aims at (a) providing a unified abstract representation of digital objects stored in heterogeneous Digital Repositories independently of the software and location and (b) facilitating the development of complex reusable digital library service components. Its integration within federated digital library architecture promotes the creation of large scale distributed digital libraries, providing the same functionality as in the case where all digital content was stored in a single digital library system.