RE: [dita] clarifying the href attribute in the language reference

["Grosso, Paul" <pgrosso@ptc.com>]

> -----Original Message-----
> From: Erik Hennum [mailto:ehennum@us.ibm.com] 
> Sent: Wednesday, 2007 May 16 15:48
> To: Eliot Kimber
> Cc: DITA TC list
> Subject: Re: [dita] clarifying the href attribute in the 
> language reference
> 
> Hi, Eliot, Paul, and TC:
> 
> Should the rephrase bring out these main points:
> 
> * The value of a DITA href is a URI.

Yes, and we should note that implies certain character
restrictions, and we need to say something about what
should happen when the value isn't a valid URI (even
if we leave that implementation dependent).

> 
> * A URI without a hash resolves to the top element in the file

We shouldn't talk about how a URI "resolves" (or what it
"references"), since that's in the realm of RFC 3986.  So...

> except where the top element is a <dita> element and the 
> reference must resolve to a single topic, in which case the 
> URI resolves to the first contained topic.

...I think you've got the right idea, but we need to phrase
it in terms of what the href attribute is addressing (as
opposed to what the URI resolves to).

> 
> * A URI with a hash must have a valid DITA local identifier 

s/A URI with a hash/An href value containing a hash/

> as the portion after the hash. A DITA local identifier 
> consists of topicID/elementID for a subelement of a topic and 
> of elementID for topics, maps, and map subelements.
> 
> As long as we're nailing down the description of href, are 
> there any special considerations having to do with IRIs [1]? 
> I wouldn't expect so, but I have a shallow understanding of 
> IRIs and translation issues in general.
> [1] http://tools.ietf.org/html/rfc3987

There could be.  (I was hoping to avoid this question for
the sake of simplicity, but it is actually a good question.)

IRIs are a superset of URIs.  IRIs allow more characters.
However, IRIs have to be mapped into URIs before they
actually get used to retrieve something, so there is more
work involved.

HRRIs [2] are a superset of IRIs.  Repeat previous story
for yet another layer of the onion.

The value of things like XLink hrefs and XML system identifiers
are really HRRIs (clarification is in progress in the W3C), so
one could make an argument that our hrefs should be HRRIs.

For now, if we want to avoid complexities, we could say that
hrefs are URIs.  That allows us to open them up to IRIs and
HRRIs later, since URIs are the most restrictive.

paul

[2] http://www.ietf.org/internet-drafts/draft-walsh-tobin-hrri-01.txt