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> -----Original Message----- > From: Mark Baker [mailto:distobj@a...] > Sent: Sunday, December 30, 2001 5:25 PM > To: jackpark@t... > Cc: xml-dev@l... > Subject: Re: XML "tuple spaces" alpha technology > demonstrated > > > but before we run off and create something > new, I'd ask you all to consider that HTTP itself is a protocol that > implements a coordination language similar to Linda in some important > ways, but with some additional important characteristics that Linda > never considered that may explain why it got deployed and Linda > didn't. I (and I suspect the RogueWave and JXTA-spaces people as well) would completely agree that any XML "spaces" solution must either be layered on HTTP/WebDAV or have an HTTP binding to have any chance at success. JavaSpaces dependence on Jini was almost certainly the largest nail in its coffin. [I'd also assert that it's reliance on strong typing makes it less useful in a loosely coupled environment than Linda or Ruple, but that's another thread :~) ] I think of the various XML spaces as being at the layer above SOAP -- they provide an additional layer of services that doesn't come for free in HTTP or SOAP, and a Linda-like coordination protocol would have about the same architectural relationship to SOAP as RPC has. Specifically, the various "spaces" implementations offer the basic read/GET and write/PUT operations that HTTP does, but also: - "take" (GET and DELETE in an atomic operation), - associative lookup (XML databases such as Tamino do this with XPath on top of HTTP, but it's not part of HTTP or WebDAV at present) - "leases" (automatic cleanup of entries that nobody "takes" after a specified period of time) - security (Ruple adds digital signature support for encryption an non-repudiability). Wouldn't using raw HTTP as the coordination protocol require some more sophisticated application-level logic to provide analogous services? As Gavin has noted, this is not easy for ordinary developers to grok, so a "spaces" service layer on top of HTTP makes sense to me.
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