- From: Ivan Herman <ivan@w3.org>
- Date: Thu, 30 Apr 2009 11:09:55 +0200
- To: Manu Sporny <msporny@digitalbazaar.com>
- CC: RDFa Developers <public-rdf-in-xhtml-tf@w3.org>
- Message-ID: <49F96AE3.4030308@w3.org>
Ivan Herman wrote: > > Manu Sporny wrote: >> Ivan Herman wrote: >>> - Is the following acceptable: @prefix="=http://a.b.c/" ? >>> my option would be yes, and it sets the default namespace. >>> It could be equivalent to a xmlns="http://a.b.c/" >> Most of this discussion about changing the default namespace has >> happened offline over the past couple of months. During the telecons, we >> didn't discuss in detail or form a consensus on how one would override >> the default namespace. >> >> The other option that has been floated over the past couple of months >> was using a reserved word, so something like: >> >> @prefix="DEFAULTNS=http://a.b.c/" >> > > I do not have very strong feeling about this but, I must admit, I am not > sure I like the keyword approach, it adds yet another reserved term > which is not good. I do not believe many people would use the default > namespace stuff (after all, in 99% of the cases the default namespace is > set by the surrounding language, eg, XHTML). > > >> We could discuss further if a number of people felt that we needed a >> mechanism to override the default namespace. It seems like we really >> should define such a mechanism. >> >> Personally, I'd prefer a reserved word mechanism over the other method >> because: >> * It would probably be easier for non-developers to understand. > > 99.9% of the non-developers would not even consider this stuff in my > view. They would just go with the namespace mechanism and rely on the > surrounding language (XHTML) to have a default namespace. Ie, we should > not go out of our way for this... > >> * It would be harder to mistakenly override the default namespace. > > Yes, that is a reasonable point... > >> * It would be easier for the parser writers to handle. >> > > I am not sure of that... I retract this! I just ran into the situation while testing and, indeed, it can be a bit tricky if there is nothing on the left side of the '='. It becomes more complicated to differentiate between a=AAA =qqq that might have been a legitimate use with qqq being a default namespace and a= AAA=qqq which is the 'illegal' usage of an empty URI (the point below). Sigh... Ivan > >>> - Is the following acceptable: @prefix="aa=" >>> my option would be no, this is an error, and the RDFa >>> processor should simply ignore that >> I believe that the current regex would not match "aa=" and would thus >> ignore it. However, if one were to do prefix="aa= bb=http://foo.com", >> that may cause an issue. We should really have a couple of approved test >> cases for these error conditions in the Design Suite. I'll try and take >> an action to create some valid Design Suite test cases for @prefix. >> > > Ie, we agree that this is an error, right? > >>> - What happens if there is, on an element, both an xmlns and a prefix? >>> Ie, if I have >>> >>> <bla xmlns:aa="http://www.w1.com/" prefix="aa=http://www.w2.com/"/> >>> >>> what is the URI corresponding to the "aa" prefix? I know there were >>> discussions on the task force, but it is not documented on the wiki... >> There are currently mixed feelings on this. At first, we believed that >> xmlns and prefix would exist in the same language, but now there are >> concerns that this may confuse people (having two ways to do the same >> thing). This issue can be worked through, so let's assume that prefix >> and xmlns can be defined in the same document. >> >> I believe that the current consensus is that you would process both >> lists, but one would take precedence over the other. > > I agree. We should be prepared to have both (although future DTD-s could > make one or the other not well formed, but that is another matter). > Other than that we would force our tools to run in two 'modes' which > complicates matters. > >> So, for example, if >> @xmlns took precedence over @prefix, you would process @prefix first and >> then @xmlns. Any conflicting mappings would be overwritten when @xmlns >> is processed. The last defined value wins. >> > > Exactly. So here is the $1000 question: what is the precedence? At the > moment, in my tool (on my machine, that is) @prefix has a higher > precedence, ie, that one wins, but it is really throwing a dice, as far > as I am concerned. We just have to document the result of throwing it > and declare victory on that one... (I do not really see a significant > advantage of one over the other) > > Ivan > > >> I have noted these issues on the rdfa.info wiki: >> >> http://rdfa.info/wiki/alternate-prefix-declaration-mechanism#Outstanding_Issues >> >> Anybody else disagree or have more input on these issues? >> >> -- manu >> > -- Ivan Herman, W3C Semantic Web Activity Lead Home: http://www.w3.org/People/Ivan/ mobile: +31-641044153 PGP Key: http://www.ivan-herman.net/pgpkey.html FOAF: http://www.ivan-herman.net/foaf.rdf
Received on Thursday, 30 April 2009 09:10:17 UTC