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   Re: [xml-dev] REST as RPC done right

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"Simon St.Laurent" wrote:
> ...
> > In my mind, the defining characteristics of RPC are a) a single
> > endpoint supports an arbitrary number of methods b) the endpoint is
> > allowed to invent its own methods and c) the endpoint returns values
> > based on the method name and method inputs.
> In my mind, the defining characteristic of RPC is that it is Remote
> Procedure Calls, passing parameters to named methods and expecting a
> result.  Your (a) and (b) strike me as nifty extra features, not
> something fundamental.

Can you name a protocol that bills itself as RPC that lacks features a)
and b)?

> > If HTTP is RPC then I would say FTP is also. HTTP calls them "methods",
> > FTP calls them "commands" but the important thing is that they are
> > defined *in the standard* (modulo extensions) rather than being defined
> > by the end-points.
> HTTP is an RPC application built on TCP/IP.  

If you want to say that HTTP is an RPC *application* then that's very
different than saying that HTTP is an RPC protocol. It's as different as
RSS's relationship to XML. They are totally different levels.

HTTP certainly could have been defined as an RPC application except that
the "RPC protocol" that it builds upon is not documented and not used
for any other application protocol. So it is at best a virtual RPC

> ... The fact that the method
> calls are defined *in the standard* doesn't change much about that, and
> HTTP certainly allows for extensible parameters in any case.

You didn't touch my question about FTP, or SMTP or POP for that matter.
You send the UIDL "method" and get back values. Is POP RPC?

> I can certainly define standard non-extensible protocols which happen to
> use XML-RPC or SOAP.

But those are not RPC protocols. They are applications of RPC. For
example, UDDI is not an RPC protocol.

I'll repeat that HTTP could certainly have been defined on top of an RPC
protocol without having suffered any harm. It wasn't, probably because
there was no appropriate RPC protocol available at the time. So it isn't
the case that everything that RPC touches immediately falls apart. It's
rather the case that the RPC layer is not a very important or helpful
layer which is why you can get away without defining it formally. The
RPC layer only takes on mythic proportions when people start to revel in
the ability to invent their own protocols on top of it...and that's
where interoperability starts to degrade.

 Paul Prescod


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