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Re: RDDL2 Background

From: Eric van der Vlist <vdv@dyomedea.com>
Date: Mon, 19 Jan 2004 22:51:29 +0100
To: www-tag@w3.org
Message-Id: <1074549089.24871.679.camel@delleric>

On Mon, 2004-01-19 at 20:19, Tim Bray wrote:
> I've been seeing the grumbling about RDDL2, and in fact it's kind of 
> unfair to ask people to react to it without a bit of the rationale 
> behind it.  So let me provide that.  I'll post a pointer to this 
> message to xml-dev too.
> Here's the original idea for RDDL: "We want a namespace document that's 
> human-readable (to explain what the namespace is all about) and 
> contains a machine-readable directory of related resources, like 
> schemas and stylesheets and renderers and so on.  We'll identify the 
> related resources by "Nature" (mime type or namespace name) and 
> "Purpose" an extensible list of things you might use them for.
> The community, including everyone from solo hackers to the Microsoft 
> Office group, reacted well to this premise, and Jonathan (mostly) and I 
> cooked up RDDL.  There were some problems with RDDL, though.
> 1. the "Nature" attribute was labeled role= and the "Purpose" attribute 
> was
>     labeled arcrole=; or maybe I have that backward, I never could 
> remember.
>     Reasonable people kept asking why nature wasn't called "nature" and 
> purpose
>     wasn't called "purpose".
> 2. If you read the semantics of the XLink spec, RDDL1 was arguably 
> abusing
>     them pretty severely.  XLink's design is highly optimized for 
> support of
>     human-facing apps, whereas the linkage in RDDL was designed from the 
> start
>     for machine-readability.  Also the choice of role= and arcrole= for 
> nature
>     and purpose was really hard to defend, you could have switched them 
> and
>     defended it just as easily
> 3. RDDL1 also included a bunch of other stuff that was duplicated by 
> markup
>     already present in HTML, in which it was designed to be embedded.

No, that wasn't the case: the link for machine consumption isn't always
the same than the link(s) for human consumption. In all the RDDL
documents I have written they are actually different. That is, their
source is always different and their target is sometimes different too.

> So I cooked up RDDL2, which used the existing mechanisms in XHTML and 
> had a whole lot less markup, and I thought did a lot better job of 
> hitting the 80/20 point.

I don't think so, unless all my (real world) use cases are outside your

> The one thing it loses that RDDL1 gave you, as Eric points out, is the 
> ability to have a bunch of marked-up descriptive text *inside* your 
> related-resource link.  I'm having trouble getting upset about that, 
> since it seems that the marked-up text is aimed at humans, while the 
> nature/purpose link is aimed at machine-readability. 

Let's say I want to store in a database (either a XML or a RDF database)
information about the resources. With RDDL 1.0 I can store full and rich
descriptions of each resource which is something really meaningful while
with RDDL 2.0 I can store only small pieces of text.

That removes 80% of the interest of RDDL to me ;-) ...

If XLink is really the problem, let's define a rddl:resource element
with nature, purpose and ref attributes, but is this really worth making
a version 2.0?


>  -Tim
Curious about Relax NG? Read my upcoming book online.
Upcoming XML schema languages tutorial:
 - Santa Clara  -half day- (15/03/2004)        http://masl.to/?J24916E96
Eric van der Vlist       http://xmlfr.org            http://dyomedea.com
(ISO) RELAX NG   ISBN:0-596-00421-4 http://oreilly.com/catalog/relax
(W3C) XML Schema ISBN:0-596-00252-1 http://oreilly.com/catalog/xmlschema
Received on Monday, 19 January 2004 16:53:07 UTC

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