Information systems have moved from centralized systems to client-server environments. Our DLs therefore may follow that same path; scalability makes it almost obligatory.
The Hyper-G system deals with scalability by restricting clients to generally connect to a local server. Local servers cache data, and access other Hyper-G servers as needed to get desired information. Local servers index and search full-text documents, and maintain their part of the distributed link database.
The Networked Computer Science Technical Report Library (NCSTRL) accomodates its Lite sites with a central server. Standard sites provide full service, supporting local search. The backup server (at Virginia Tech) handles searches for any server not available. Thus, NCSTRL supports a combination of centralized and distributed searching.