Re: [model] Clarifying annotation architecture

> On 4 Aug 2015, at 18:10, Robert Sanderson <azaroth42@gmail.com> wrote:
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> 
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>> On Tue, Aug 4, 2015 at 2:43 AM, Ivan Herman <ivan@w3.org> wrote:
>> > On 04 Aug 2015, at 24:30 , Robert Sanderson <azaroth42@gmail.com> wrote:
>> > In my mind, if you don't give an Embedded Textual Body a URI (i.e., if you let it default to a blank node) then that Embedded Textual Body will not be reused outside the current Annotation, and therefore the role assigned to Embedded Textual Body in the context of the current annotation is the only role which this particular instance of the string will ever have.
>> >
>> > That's true if you're the server providing the Annotation with a blank node body ... but on receipt of an Annotation, servers MUST assign a URI to the annotation, and MAY assign them to all other nodes.  Suddenly your blank node becomes a real resource and can be referenced from outside of the annotation.
>> 
>> Hm. Why? I think that would be an error.
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> I don't follow ... what would be an error? Assigning a URI to a blank node (skolemization) or referring to the resource from outside of the annotation (linked data)?  
>  

Sorry, I inserted the remark at the bad place. I referred to the issues below.

>> I am not sure why a URI must be assigned to a blank node body. However, it indeed it must, then (just as in any other RDF environment) I believe it is a requirement that URI-s assigned to a body must be unique.
> 
> It doesn't have to be, but some systems will just do it for you.  The best practices of linked data are to avoid blank nodes, after all. 

Yeah, well, I do not think we should be religious about it. In my view, using blank nodes for the situations we are discussing here is perfectly fine.

> The use case I gave earlier was if you want to annotate the body and particularly if you're using a selector, it needs a URI to be the target of the second annotation.  You can't target the annotation and mean the body, as it would be ambiguous in the case we're discussing of multiple bodies.

I am lost. I think Tim's example was for the resources used as an encapsulation for the body and a motivation. That one does not really need its own URI. That is where blank nodes are perfectly fine.

>  
>> See also what the RDF 1.1 concept document says about this:
>> 
>> [[[
>> In situations where stronger identification is needed, systems MAY systematically replace some or all of the blank nodes in an RDF graph with IRIs. Systems wishing to do this SHOULD mint a new, globally unique IRI (aSkolem IRI) for each blank node so replaced.
>> ]]] http://www.w3.org/TR/rdf11-concepts/#section-skolemization
>> 
>> There is also a skolemization approach described in that section. We can even require a MUST instead of a SHOULD for this.
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> Exactly :)  As we don't know when stronger identification is needed a priori, we should assume that it will be in some situations, and design the model accordingly.
> 

I do not understand what you mean here. My only comment was to say is that if the system chooses to provide a URI to blank nodes (ie, it skolemizes the blank nodes), we can safely assume and even require that the resulting URI-s will be different for different blank nodes. 

Ivan



> Rob
> 
> -- 
> Rob Sanderson
> Information Standards Advocate
> Digital Library Systems and Services
> Stanford, CA 94305