Re: [Simple] PIDF "entity" attribute usage

Tim Rang wrote:
> Folks,
> 
>  
> 
> In nearly all of the I-Ds related to presence, every example pidf 
> document I find contains an entity attribute with a “pres” scheme.  The 
> schema for RFC 3863 indicates that any URI is acceptable here.  However, 
> section 4.1.1 states-
> 
>                The value of the 'entity' attribute is the 'pres' URL of the PRESENTITY publishing this presence document.
> 
>  
> 
> Recently, I’ve started to see some instances where the entity attribute contains a sip scheme (Ex- draft-ietf-simple-presence-data-model-01
> 
> ).
> 
>  
> 
> My questions are:
> 
> -          What is the intended usage of this entity attribute in SIMPLE?

It identifies the entity that the pidf document describes.
In many cases you should already know that (because you subscribed to 
it) and in those cases it may be redundant. In other cases, such as when 
you have used an RLS to subscribe to a list of presentities, it is 
important information.

The URI it contains also is usually what you use to request presence.

> -          What is the meaning of the ‘pres’ scheme and why should we 
> use it over something more relevant (i.e. ‘sip’)?

The original work on presence was done by the IMPP WG. The PIDF and CPIM 
specifications were intended to be protocol independent - allowing 
multiple IM&Presence protocols to be developed that could interoperate.

One aspect of this is having a presence URI scheme ("pres") that is 
itself independent of the protocols that are used to access it.

SIMPLE is one protocol specific realization of the presence 
functionality defined by IMPP. Of course it is built on SIP, and so SIP 
URIs are natural for identifying presentities in SIMPLE. However the 
means by which pres URIs can be used with SIMPLE is also defined.

So, at least in principle, when using SIMPLE, you can use either sip or 
pres URIs. However this assumes the specific implementation you are 
using actually supports this. In practice you should determine what the 
implementation you are using supports.

	Paul

> Thanks,
> 
> Tim Rang
> 
> 
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