Please pardon me for entering this thread a few weeks later, but stepping out side of REST, this reminds me of some of the emerging Web Services specs. More comments at end.

"K. Ari Krupnikov" wrote:

Stepping away from REST for a second (but acknowledging that REST was your main intent), this is the essence of service-oriented architectures (SOAs) - shared (non-redundant) business logic encapsulated as shared services that can be published, discovered, and bound/invoked (at design time and/or run time). The coordination aspects you discuss above are covered by emerging specifications such as IBM/Microsoft/BEA's WS-Coordination/WS-Transaction (WS-Transaction is now segmented into 2 specs, WS-AtomicTransaction and WS-BusinessActivity) [1][2], WS-Resource Framework (WSRF) [3] from the Globus Alliance/IBM/HP, and OASIS Composite Application Framework [4]. References [1][2][4] involve the specification of a "coordinator" that coordinates the actions of multiple Web services for requirements such as 2-phase commits, error notification, etc. Reference [3] addresses interations of Web services with stateful resources.

It is important to note that none of these specifications are "open standards" (in OASIS and W3C-"like" terms) - the one closest to becoming an open standards at this point is WS-CAF.

Kind Regards, Joe Chiusano Booz | Allen | Hamilton Strategy and Technology Consultants to the World

[1]
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnglobspec/html/wscoor.asp [2]
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnwebsrv/html/wsacoord.asp [3] http://www-fp.globus.org/wsrf/ModelingState.pdf [4] http://www.oasis-open.org/committees/tc_home.php?wg_abbrev=ws-caf