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RDDL2 Background

From: Tim Bray <tbray@textuality.com>
Date: Mon, 19 Jan 2004 11:19:19 -0800
Message-Id: <616E9E20-4AB4-11D8-905C-000A95A51C9E@textuality.com>
To: www-tag@w3.org <www-tag@w3.org>

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.

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.

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.  -Tim
Received on Monday, 19 January 2004 14:19:56 GMT

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