Re: [xdi] $is is the universal inverse restriction

["Giovanni Bartolomeo" <giovanni.bartolomeo@uniroma2.it>]

Hello Drummond,

I see what you mean.. but, apart from the reason to have $is as the  
operator for producing inverse predicates - which I still need to  
think about but I know it has been historically shared among TC  
members :-) - what's the semantics of predicate ($xdi$v$1)? And what's  
the intended usage of brackets () in

> =drummond
>    ($xdi$v$1)
>      $

?

Kind Regards,
Giovanni

Def. Quota "Drummond Reed" <drummond.reed@xdi.org>:

> Although I was not able to attend the last TC call, Giovanni and Joseph
> Boyle (our newest TC member -- welcome Joe!) still held a chat thread. On
> that thread, they discussed a line of the example PDX document that I posted
> to http://wiki.oasis-open.org/xdi/PdxExample last week.
>
> The line was right near the start:
>
> $   <-- Pattern: Context Self Descriptor -->
>         $is$a
>                 ($xdi$v$1)      <-- Pattern: Context Type -->
>                 ($pdx$v$1)
>         $is($xdi$v$1)   <-- Pattern: Context Authority -->
>                 =!1111.aaaa.bbbb.cccc!9999.xxxx.yyyy.zzzz
>
>
> They were discussing what the predicate "$is($xdi$v$1)" meant.
>
> I thought this was fairly straightforward from the definition of $is as the
> universal XDI inverse predicate when used as a restriction on any other XDI
> predicate. Examples:
>
> PREDICATE               INVERSE
> +father                        $is+father
> +author                       $is$author
>
> EXAMPLES
>
> =gardner/+father/=drummond
> =drummond/$is+father/=gardner
>
> +davinci.code/+author/=dan.brown
> =dan.brown/$is+author/+davinci.code
>
> So, the statement
>
> $
>   $is($xdi$v$1)
>      =drummond
>
> ...is the equivalent to saying
>
> =drummond
>    ($xdi$v$1)
>      $
>
> ..which is simply a way of sayiing that the current XDI context (XDI
> document, represented by $) is the XDI V1 context of ("belongs to") the
> personal authority with the identifier =drummond.
>
> This illustrates that the semantics of $is, when used as a restriction
> (i.e., before ANY other XDI predicate), are simply that it is the inverse of
> the predicate it restricts (i.e., the entire predicate that follows it).
>
> This is of course true of $is$a, $is$has, and $is$has$a, just like all other
> inverse predicates.
>
> Hope this helps - I love it that the semantics of $is are the simplest but
> in some ways one of the most powerful of all XDI predicates.
>
> =Drummond
>
>
> On Fri, May 28, 2010 at 1:53 AM, Giovanni Bartolomeo <
> giovanni.bartolomeo@uniroma2.it> wrote:
>
>> Hello, Drummond, Bill..
>>
>> no problem. We just started discussing the PDX sample document and this led
>> to raise some issues... Hopefully during next phcs there will be time to
>> discuss in details these points and the rest of the document.
>>
>> Kind Regards,
>> Giovanni
>>
>>
>



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