D. Retrieval Processor
Retrieval Processor is the component that gathers response sets from Index Generator and presents them to end-users. In the simple case of a query being delivered to a single Index Generator, Retrieval Processor might not be necessary. But with grid-based information retrieval, querying many federated data sets over time is envisioned, and sophisticated merger and presentation of results will occur. Thus, Retrieval Processor is envisioned as the solution to some of WAIS’ shortcomings, as well as a repository for standing queries (information filtering) and a tool for data presentation.