Description of RCDS

The Resource Cataloging and Distribution System (RCDS) consists of the following components:

• Clients, which are the consumers of the resources provided by the system. One kind of RCDS client is an ordinary WWW browser with slight modifications to make use of the resolution system. Unmodified WWW browsers can also access RCDS through the use of a RCDS-aware proxy server.
• File servers, which provide access to the files themselves. These can be ordinary general-purpose file servers that use http, ftp, nntp, imap, NFS, or some other file access protocol, or servers that use a protocol designed for some special purpose (such as those designed for the real-time transmission of audio or video), or even multicast transmission sources.
• Resource catalog servers, which maintain information about the characteristics of network-accessible resources and accept queries about the characteristics of such resources from clients.
• Location servers, which maintain information about the locations of network-accessible resources, and accept queries for location data from clients.
• Collection managers. The collection of files on a file server is maintained by a collections manager, which learns about newly published files and determines when a file server should acquire replicas of new files and reap old ones, according to site-specified criteria. The collections manager is also responsible for actually acquiring and deleting the chosen files. Finally, when a new file is added to the collection or an old one removed, the collections manager informs the location servers about changes in file availability.
• Publication tools, which accept new files and descriptions from content providers (e.g. authors), and inject them into the system.
• SONAR, which allows a choice of locations to be made by an RCDS client. Given several alternative locations from which to access a resource, an application program can query a nearby SONAR server to determine which locations are closer than others. The SONAR server will return, for several of those locations, a metric which provides a rough indication of the proximity of that location to the SONAR server. Using those metrics, the application can then choose a single location from those returned from which to access the resource.

 
• Resource names
  • URNs and LIFNs
  • Format of URNs and LIFNs
  • Resolution of URNs and LIFNs
• Publication and Distribution
• Access and Retrieval