W3C home > Mailing lists > Public > uri@w3.org > March 2004

Re: grammar fix for path

From: Graham Klyne <GK@ninebynine.org>
Date: Fri, 26 Mar 2004 09:38:06 +0000
Message-Id: <>
To: "Roy T. Fielding" <fielding@gbiv.com>
Cc: uri@w3.org

At 18:51 25/03/04 -0800, Roy T. Fielding wrote:

>On Tuesday, February 17, 2004, at 04:01  AM, Ray Merkert wrote:
>>I was just in the middle of looking at IRIs, when I noticed something 
>>strange. It seems the
>>URI 'http://w3c.org:80path1/path2' has become a valid URI, at least 
>>according to the
>>collected BNF grammar in draft-fielding-uri-rfc2396bis-04.txt.
>I have tried various ways of explaining it in the text and finally
>went back to multiple definitions of path, though I hope I've done
>a better job of disambiguating the different cases than I did for
>2396.  I would appreciate it if the grammar-driven parsing experts
>could have a look at
>    http://gbiv.com/protocols/uri/rev-2002/rfc2396bis.html  (or .xml)
>and see if the new ABNF rules work (I've already tested them with
>the abnf.c tool).

I'll try this out when I have some time... it may be a week or 
so.  meanwhile, a quick point of confirmation concerning:
If a URI contains an authority component, then the path component must 
either be empty or begin with a slash ("/") character. If a URI does not 
contain an authority component, then the path cannot begin with two slash 
characters ("//"). In addition, a URI reference (Section 4.1) may begin 
with a relative path, in which case the first path segment cannot contain a 
colon (":") character. The ABNF requires five separate rules to 
disambiguate these cases, only one of which will match a given URI 
reference. We use the generic term "path component" to describe the URI 
substring that is matched by the parser to one of these rules.

This suggests to me that the minimal authority "//" is distinct from having 
no authority at all, which I think is fine.  In particular, I think the 
above text means that it is not OK to remove a minimal "//" authority from 
a URI.  (I always believed this to be the case, but I have encountered 
software that does remove "blank" authorities.)


Graham Klyne
For email:
Received on Friday, 26 March 2004 05:14:03 UTC

This archive was generated by hypermail 2.3.1 : Tuesday, 6 January 2015 21:25:07 UTC