Re: non opaque primary topics

I've also seen #_

Juan Sequeda
+1-575-SEQ-UEDA
www.juansequeda.com


On Mon, May 13, 2013 at 11:56 AM, Melvin Carvalho
<melvincarvalho@gmail.com>wrote:

>
>
>
> On 9 May 2013 02:28, Tim Berners-Lee <timbl@w3.org> wrote:
>
>>
>>
>> On 2013-05 -07, at 17:08, Melvin Carvalho wrote:
>>
>> > the standard model in sem web seems to be
>> >
>> > <> foaf:primaryTopic <#relative-uri>
>> >
>> > I've seen 4 relatively common relative URIs used here and there
>> >
>> > 1. #me -- common in foafs
>> > 2. #i -- often used by timbl and tobyink
>> > 3. #this -- used by kingsley as per the 'this' keyword in OO
>> > 4. # -- used by facebook and others
>> >
>> > It's a very common case that a document will contain one primary topic
>> and I want to standarize all of my pages (mainly robots) into one of these
>> 4.
>> >
>> > It seems to me that (4) is the most sensible choice, after "it doesnt
>> matter".
>> >
>> > Does anyone have any preference here?
>>
>> A URI takes the form
>>
>>           <document identifier>  #  <local identifier>
>> or
>>           <document identifier>
>>
>> The point about this is that all kinds of languages can talk
>> about the same thing in different ways.   To get interopabiliity,
>> though, you have to stick to a limited set of local identifiers which
>> will work in any language.
>>
>> So having the empty string as a local identifier does
>> in fact work in RDF.  But it is a pain.
>>
>> You can't use qnames with an empty localid:
>>
>> > 1. :me -- common in foafs
>> > 2. :i -- often used by timbl and tobyink
>> > 3. :this -- used by kingsley as per the 'this' keyword in OO
>>
>>
>> Ooops! facebook's empty localid isn't allowed as a localid.
>>
>
> Ah Thanks.  I was unaware of this difference between qnames and ntriples.
> It does seem that the empty fragment could be unsafe.
>
> However I think that qnames are predominantly (maybe always?) used in the
> predicate position, so this makes facebook profiles still OK?
>
>
>>
>> That means also when machines later re-serialize your data,
>> they won't be able to use the qname syntax.
>>
>> Of course lots of other languages have restrictions that
>> identifiers have length  > 0.
>>
>> So, while for facebook I'm not complaining that they
>> are using turtle, I wouldn't advice anyone to use an empty localid.
>>
>> Of the other 3 forms, take your pick.   I must say I  used
>> :i but I find it less easy to explain than :me. Another possibility
>>  for a FOAF file is #timbl  which might have
>> read better when explaining to a class.
>>
>> But as someone else said the string you use does not
>> is opaque in the system and so :x or :it   is fine.
>> I quite like :it if you are generating stuff automatically.
>>
>>
>>
>> Tim
>>
>>
>>
>