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Re: section 1, intro, for review

From: Roy T. Fielding <fielding@apache.org>
Date: Wed, 20 Mar 2002 16:13:05 -0800
To: David Orchard <david.orchard@bea.com>
Cc: www-tag@w3.org
Message-ID: <20020320161305.A2012@waka.wakasoft.com>
On Tue, Mar 19, 2002 at 10:12:52PM -0800, David Orchard wrote:
> Roy,
> 
> I'd like to understand your rant a bit more.  This shouldn't be interpreted
> as agreement, just me seeking understanding.  I think you are saying that if
> people want to create object-specific interfaces using URIs, XML, HTTP, then
> they shouldn't call it anything to do with the web.  More like "XML Internet
> Services" or something like that.  That the notion of a shared information
> space with well-defined interfaces is core to the web.  Not usage of URIs,
> HTTP, Markup.  Those are helpful and interesting and good practice and ....
> but not core to the web.

It is also core to HTTP.  SOAP is not HTTP compliant because it ships
actions with the content that contradict the application semantics described
in the control data of an HTTP message.  That breaks intermediares.

SOAP over something like BEEP does not suffer from that problem and I would
call that an XML service on the Internet.

> Further, attempts to put object interfaces onto the web - like
> CORBA/DCOM/RMI - failed because they didn't use well-defined interfaces.

You mean objects interfaces on the Internet, right?

No, they had very well defined interfaces.  Exceptionally well.  Defined
so well that they made an application exceedingly fragile to version drift
and differences between ORBs.  Hence, they did not survive multiple
organizational boundaries when deployed as application infrastructure.

> Their "failure" has nothing to do with complexity,

Complexity was due to object-specific interfaces.

> lack of implementations,

They far outnumbered Web implementations at the time.

> too early to market, binary formats, bootstrap problems, no buy-in across a
> big enough community or other issues.  I think that this implies that if
> CORBA/DCOM/RMI had used HTTP PUT/POST/DELETE/GET in a RESTful style, they
> would have had a much better chance of success.  You said this was the
> lesson to learn from their failures.

I think so, yes.  The money placed on CORBA and DCOM, separately, dwarfs
that spent on the Web.  But CORBA/DCOM/RMI are all distributed object
architectures, so it wouldn't have made any sense for them to be REST-like.
REST doesn't use strong typing and focuses on data streams rather than
parameter values.  They are different beasts.  The point is that we lose
the properties that makes the Web work when we introduce strong typing,
object-specific interfaces, etc.

> Expressed a different way, the web succeeded because it was loosely coupled.
> The use of well defined interfaces is the essensial element in this loose
> coupling.  The use of well-defined interfaces allows clients and servers to
> communicate without knowing the specifics of the resource.  Putting an
> object interface onto a URI effectively tightly couples the sender/reciever
> in a way that should never be considered part of the web.  The problem with
> a non well-defined interface is that the client now has to discover the
> interface (or whether it's changed) and create/change the sending messages.
> With well-defined interfaces, the components can talk to each other without
> this discovery/interface compilation step, which will scale/adapt/perform/be
> more reliable, etc.

The difference between well-defined object-specific interfaces and defined
uniform interfaces is that the latter scales better with intermediaries
and with unanticipated forms of client.

....Roy
Received on Wednesday, 20 March 2002 19:16:39 GMT

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