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Re: up up up, was: Last Call: draft-nottingham-http-link-header (Web Linking) to Proposed Standard

From: Toby Inkster <tai@g5n.co.uk>
Date: Tue, 1 Sep 2009 10:22:16 +0100
Message-Id: <AA53F24B-D369-4894-AAFD-85EC7016A7A0@g5n.co.uk>
Cc: "public-html@w3.org" <public-html@w3.org>, Ian Hickson <ian@hixie.ch>, Mark Nottingham <mnot@mnot.net>
To: Julian Reschke <julian.reschke@gmx.de>
On 30 Aug 2009, at 13:24, Julian Reschke wrote:

> The main disadvantage is that a recipient that only looks for "up"  
> and which tries to build a tree of resources, treating "up up up"  
> as "up" will create a broken tree.

How does "up up up" fit in with hierarchies where nodes may have  
multiple ancestries?

e.g. the "Winston Churchill" article in a theoretical encyclopaedic  
work might be reachable by drilling down in any of the following ways:

	Home
	-> People
	   -> British
	      -> Prime Ministers
	         -> 20th Century
	            -> Winston Churchill

	Home
	-> People
	   -> Families
	      -> Spencer-Churchill Family
	         -> Winston Churchill

	Home
	-> Events
	   -> Wars
	      -> World War II
	         -> Key Players
	           -> Winston Churchill

The first tree implies that the relationship from Winston Churchill's  
page to the home page is rel="up up up up" and the second tree  
implies that it's rel="up up up". The last tree also implies rel="up  
up up up".

The rel attribute allows multiple relationships to be space- 
separated, so I can imagine someone adding links to Winston  
Churchill's page like this:

	<link rel="up up up home up up up up contents up up up up" href="/" />

RDFa provides a solution to mapping out the full tree of "ups"  
unambiguously:

	<link rel="home contents" href="/" />
	<link rel="up" href="/People_GB_PM_20C" />
	<link about="/People_GB_PM_20C" rel="up" href="/People_GB_PM" />
	<link about="/People_GB_PM" rel="up" href="/People_GB" />
	<link about="/People_GB" rel="up" href="/People" />
	<link about="/People" rel="up" href="/" />
	<link rel="up" href="/Family_SpencerChurchill" />
	<link about="/Family_SpencerChurchill" rel="up" href="/Families" />
	<link about="/Families" rel="up" href="/People" />
	<link rel="up" href="/WW2_KeyPlayers" />
	<link about="/WW2_KeyPlayers" rel="up" href="/WW2" />
	<link about="/WW2" rel="up" href="/Wars" />
	<link about="/Wars" rel="up" href="/Events" />
	<link about="/Events" rel="up" href="/" />

Or, for a more visible, breadcrumb-like solution:

	<div class="breadcrumbs">
	  <a rel="home contents" href="/">Home</a> &lt;
	  <a about="/" rev="up" href="/People">People</a> &lt;
	  <a about="/People" rev="up" href="/People_GB">British</a> &lt;
	  <a about="/People_GB" rev="up" href="/People_GB_PM">Prime  
Ministers</a> &lt;
	  <!-- etc -->
	</div>

-- 
Toby A Inkster
<mailto:mail@tobyinkster.co.uk>
<http://tobyinkster.co.uk>
Received on Tuesday, 1 September 2009 09:23:00 UTC

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