W3C home > Mailing lists > Public > xml-uri@w3.org > May 2000

Re: Namespace names: a semi-serious proposal

From: Paul W. Abrahams <abrahams@valinet.com>
Date: Sat, 27 May 2000 12:26:07 -0400
Message-ID: <392FF71F.D67433D2@valinet.com>
To: Tim Berners-Lee <timbl@w3.org>
CC: abrahams@acm.org, xml-uri@w3.org
Tim Berners-Lee wrote:

> Let's pop the stack - while it is useful to have shared context about
> URIs and what they can do, and this list may be a way to get it, the
> most essential point is that XML does not need to specify anything
> about particular schemes.
>
> The reason for using a URI is that you
> _separate_ the design issues associated with any particular URI
> scheme from the design of the language.   In other words,
> discussions like these are broken into two parts: the design of the
> language in terms of URIs, and the design of the URI schemes.
> Temping though it is for the users of URI schemes to redesign XML
> (how many non-xml languages have come out of the IETF recently?)
> and the users of XML to redesign URIs,  this reduces the power and
> resilience of the whole system.  This is one of the basic reasons
> for my asking the XML designers to make it a URI pure and simple.

The reason for using URIs in the namespace spec is, presumably, that URIs have
properties that make them useful and appropriate in that application.  But if
those properties get changed, or if someone discovers that they have
implications we hadn't anticipated, then they might no longer be useful and
appropriate.   The separation of design concerns is a desirable principle, but
it can break under stress.

> This is software engineering principle of modularity.
>
> <analogy>The design of a towing hitch separates the design of car and
> trailer.
> While the designers of trailers discuss the number of cylinders a car
> should have, and the designers of cars discuss whether trailers should
> be made of fiberglass or aluminum, then nothing is ever settled.
> Once a car can provide, and trailer accept, a standard hitch then the
> customer
> can make workable system with a big enough car and a stable enough
> trailer for the job at hand.</analogy>

I don't quite understand this analogy.  If namespaces are the car and URIs are
the trailer, then what's the hitch?  And what if the trailer is redesigned so
that it transmits unacceptable forces to the car through the hitch -- but a
different hitch might dampen them?

Paul Abrahams
Received on Saturday, 27 May 2000 12:26:14 UTC

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