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Re: Few questions about REST

From: Mark Baker <distobj@acm.org>
Date: Wed, 17 Sep 2003 23:01:52 -0400
To: Sergey Beryozkin <sberyozkin@zandar.com>
Cc: www-archive@w3.org
Message-ID: <20030917230152.O15635@www.markbaker.ca>

On Tue, Sep 16, 2003 at 05:18:36PM -0400, Sergey Beryozkin wrote:
> Hi Mark,
> You said in an earlier mail :
> Just that if it's not late bound, then client software needs upgrading
> whenever new services are introduced.  The opposite isn't true, however;
> just because you are late bound, it doesn't mean you don't need client
> upgrades to access new services.  Consider an FTP client that supports
> ftp URIs; when a new scheme is introduced, it needs upgrading to be able
> to use it.  It's really the combination of the uniform interface and
> late-binding which is why the Web is so powerful; HTTP clients can
> interact with *ANY* URI (perhaps with a proxy), because HTTP semantics
> are uniform to *ALL* URI.
> Thanks for the explanation. I think I can see now how late-binding helps
> HTTP clients, especially after seeing what a proxy can do.
> This is how I see what a late-binding can do for a client :
> For example, if a document of known mime-type is fetched for the purposes of
> presentation, then it doesn't matter which scheme, http:// or custom://, was
> used,

Well, it matters for other reasons; not everybody might be using a
proxy that knows the URI scheme.. which is why "http" makes such a
fine default.

> and yes, a presentation software (a browser in a simple case) doesn't
> need to get upgraded. But if a document is of unknown mime type, then a
> presentation software will have to be upgraded.


> In other words, with late-binding, it's a layer which communicates with a
> service(s) doesn't need to get upgraded, while an application layer may or
> may not need to get updated.

Right, modulo that it's sometimes called the application layer itself.
There's no upper layer, just data flowing within that application layer.

> The same probably applies to a RESTful (SOAP or XML) client which enables a
> machine to machine communication. For example, if a new service is
> available, then as far as a SOAP client stack (which wraps/unwraps XML doc
> in/out of envelope, etc, sends and receives it) is concerned it doesn't need
> to get changed. An application layer may not need to change as well,
> provided the data returned is of known format or if those data can be
> transformed into a known format by some generic pre-processing filter.
> Otherwise, to avail of a new service's data, the application layer will have
> to get changed as well.

There's another option; the data format is generic enough to be able to
communicate the information within other non-generic formats.  i.e. RDF.



> So, late-binding does indeed reduce integration costs for a client in that a
> layer talking to (URI-)identified resources through a uniform interface
> doesn't need to get changed. This is of critical importance to the Web in
> general.


> It seems that it would also be beneficial for a SOAP client as well, though
> it's probably of less critical importance than it's for a general HTTP
> client.
> Do you agree ?

Well, up to that last part I did.  I would say that it's of critical
importance to any client using a service over the Internet, primarily
due to reasons of visibility (I assume you've read Roy's dissertation).

Mark Baker.   Ottawa, Ontario, CANADA.        http://www.markbaker.ca
Received on Wednesday, 17 September 2003 22:59:41 UTC

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