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ISSUE-76: If we fixed namespaces, does RDFa still have problems?

From: Ennals, Robert <robert.ennals@intel.com>
Date: Fri, 11 Dec 2009 00:26:36 +0000
To: "public-html@w3.org" <public-html@w3.org>
Message-ID: <EB332302649177439359CE520D92A0AFA27C8250@irsmsx503.ger.corp.intel.com>
I'd like to draw attention to a point that Sam Ruby made a while back, when we were discussing my proposal for decentralized extensibility [ISSUE-41].

It seems that one of the biggest things that people don't like about RDFa, and thus one of the biggest reasons for creating Microdata, is that RDFa uses namespaces, and namespaces are really hard to use because the meaning of prefixes varies. However, if we adopted my proposal for decentralized extensibility, then prefixes have fixed meanings, and so I believe this problem goes away.

What do people think the other big problems with RDFa are? How much do they matter? Are there ways of fixing them?

AFAICT the obvious annoyances with RDFa are:

*         Reliance on namespaces - but that can be fixed by the earlier proposal

*         RDFa requires you to declare a type to get a blank node. Does this matter? Could it be easily fixed?

*         RDFa expects @rel when the data is a link, and @property when it is content - but I quite like that

*         RDFa doesn't have a DOM API - but that can be added

*         RDFa requires an extra layer of indirection when putting one node inside another. This is because when a node has a @rel attribute, the node is the subject if the node has a type. Does this matter? Could it be easily fixed?




What am I missing?

To make this discussion more concrete, here is are a couple of examples, using the same data, written in Microdata vs RDFa, assuming that we have a fixed set of prefixes, and that we also have a fixed set of standard types and properties that don't require prefixes.

First, let's do an example where all the names we use are in the global namespace:

Microdata:
  <div itemscope>
    <p>My name is <span itemprop="name">Elizabeth</span></p>
    <img itemprop="image" src="liz.png" alt="My Photo">
   Band:
     <span itemprop="band" itemscope>
        <span itemprop="name">Jazz Band</span> (<span itemprop="size">12</span> players)
    </span>
  </div>

RDFa:
  <div type="person">
    <p>My name is <span property="name">Elizabeth</span></p>
    <img rel="image" src="liz.png" alt="My Photo">
    <span rel="band">    -- extra node needed
      <span type="Band">
        <span property="name">Jazz Band</span> (<span property="size">12</span> players)
      </span>
    </span>
 </div>

Now, an example where we use names from an external vocabulary. In this case, we assume the vocabulary has a registered prefix rather than an experimental prefix:

Microdata:
  <section itemscope itemtype="http://example.com/animals#cat">
     <h1 itemprop="name http://example.com/fn">Hedral</h1>
  </section>

RDFa with registered prefixes:
   <section type="animals:cat">
     <h1 itemprop="name animals:fn">Hedral</h1>
   </section>


When the namespace problem is taken away, what differences are still problematic?


Note that I am not advocating for any particular position. I'm just trying to explore the space.


-Rob
Received on Friday, 11 December 2009 00:27:14 UTC

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