Analysis and Evaluation of Service-Oriented Architectures for Digital Libraries

The Service Oriented Architecture (SOA) that underlies the Web Services paradigm of computing is widely regarded as the future of distributed computing. The applicability of such an architecture for digital library systems is still uncertain, as evidenced by the fact that virtually none of the large open source projects (e.g., Greenstone, EPrints, DSpace) have adopted it for internal component structuring. In contrast, the Open Archives Initiative (OAI) has received much support in the DL community for its Protocol for Metadata Harvesting, one that in principle falls within the scope of SOA. As a natural extension, the Open Digital Library project carried the principles of the OAI forward into a set of experimental derived and related protocols to create a testbed for component-based digital library experiments. This paper discusses a series of experiments with these components to confirm that SOA and a service-oriented component architecture is indeed applicable to digital library systems, by evaluating issues of simplicity and understandability, reusability, extensibility and performance

Lightweight component-based scalability

Digital libraries and information management systems are increasingly being developed according to component models with well-defined APIs and often with Web-accessible interfaces. In parallel with metadata access and harvesting, Web 2.0 mashups have demonstrated the flexibility of developing systems as independent distributed components. It can be argued that such distributed components also can be an enabler for scalability of service provision in medium to large systems. To test this premise, this article discusses how an existing component framework was modified to include support for scalability. A set of lightweight services and extensions were created to migrate and replicate services as the load changes. Experiments with the prototype system confirm that this system can in fact be quite effective as an enabler of transparent and efficient scalability, without the need to resort to complex middleware or substantial system reengineering. Finally, specific problems areas have been identified as future avenues for exploration at the crucial intersection of digital libraries and high-performance computing