Hi Kevin,

On Thu, Jul 10, 2014 at 1:43 PM, Ford, Kevin <[log in to unmask]> wrote:
> An example in the documentation of when this isn't the case is in bf:uri
> (  http://bibframe.org/vocab/uri.html ) where there is a real resource as the
> object of the bf:uri predicate.
> And thus that it could have properties like identifierQualifier,
> identifierAssigner and so forth.  Maybe that's the intent, but it doesn't really
> seem that way?

I think this is a mistake.  So, actually, thanks for bringing that to our attention.

Okay, that was one of the pieces of evidence that I was basing my opinion on, so please bear that in mind! 

> Now consider:
>   _:LotR a bf:Instance ;
>       bf:uri <http://example.com/identifiers/book1> .
>   <http://example.com/identifiers/book1> a bf:Identifier ;
>       bf:identifierValue "some string identifier here" .
> Now it becomes very odd.

Oh, yes, it is extremely odd.  The more so because every time I look at that example I think to myself, "who in their right mind would do that?"  :)

Heh :)  Well, yes, I hope that no one would do that, but following automated rules for the skolemization of blank nodes, systems might do it unwittingly... such as the examples on the site actually do today.

To pick one at random, and dropping the namespace declarations:

  <bf:Identifier rdf:about="http://bibframe.org/resources/sample-bl/007177759identifier40">

And no, I'm not trying to say that the examples were created by people not in their right mind :D Just that it's a pretty easy trap to fall into.
  Actually, my confusion comes a little later when the URI for the bf:Identifier is suddenly the same as that for the bf:Instance. Please don't misunderstand, I comprehend your overall point, but I remain confused as to why anyone would use the URI of an Instance as the URI for a bf:Identifier.  It seems like that individual is just asking for trouble.

Yes. Indeed! And hence bf:uri seems like an invitation to trouble that could be gainfully avoided.  

Anyways, in the end....
> The solution (as above) is just to use bf:Identifier, always as a blank node, for
> only identifiers that are not themselves URIs.

I think I can sign on to this, but I'm not confident that this rule resolves this particular identifier issue as I see it.  And so begins the excursion...
After reading, and re-reading, and re-reading your email and document,

Thank you for the time! And apologies for the lack of clarity that required the re-re-reading!
I can't help but think the problem is the bf:uri property itself. 
It's a property, so it should relate two things, yet I do not believe the right semantics are being captured in this case.  I agree, if you have a URI, you have a URI.  It identifies something already.  It's the "what" that I do not think is being addressed.  Is the URI an identifier for the current resource?

That was my interpretation, given the range of bf:Identifier. 

That is, is it about same-ness (some form of equivalency or owl:sameAs relationship)?  Or, given a different context, the thing you have might be a URI but the appropriate relationship is something else altogether.  Of course, you'd want to use a property that captures the nature of the relationship versus the rather non-descriptive bf:uri.  To ask all of that another way, when does one use bf:uri?

Right. If bf:uri did not assert some degree of equivalence, then it shouldn't be a subproperty of bf:identifier, described as "Number or code that uniquely identifies an entity."  (sic, I guess, as the property isn't a number of code, that's the property's range, but I needlessly digress)

Instead it could be a subproperty of bf:relatedTo ... but I have no idea how it would be any different to relatedTo.
And so...
Does this
 _:LotR a bf:Instance ;
     bf:uri <http://example.com/identifiers/book1> .

mean this?
 _:LotR a bf:Instance ;
     bf:equivalentInstance <http://example.com/identifiers/book1> .

I think so?
(I might have made up the bf property for demonstration purposes, but you get the idea.)  If so, then would it not be better to use bf:equivalentInstance, which is far more explanatory, than bf:uri?  Or is knowing the type of identifier more important?  (Really, those are not rhetorical questions.)

I think that bf:equivalent, ore:similarTo, owl:sameAs or other appropriate relationship, is the way to go.
And, given that the Identifier has identifierScheme, the type of identifier can be found out from there.
Currently it's quite possible to say the meaningless:

  _:instance bf:coden _:doi .
  _:doi identifierScheme "doi" .

Now what? Is it a DOI or a coden?
bf:hdl (http://bibframe.org/vocab/hdl) is another one that I find similarly lacking in strong semantics.  Add bf:urn to that as well.

Yup. Going though the subproperties of identifier with a fine toothed comb would be instructive, I think!
This last case is interesting because a URN is a URI.  So, to be clear, would bf:urn fall under the rule your proposed above?  (Your document would suggest as much, which is all fine by the way I'm just looking for clarification.)

As a URN is a URI then yes, it shouldn't be used with Identifier.

Does this capture the semantics better
_:LotR a bf:Instance ;
    bf:doi _:bnode1
_:bnode1 a bf:Identifier
   bf:identifierValue "10.1000/182"
   bf:identifierAssigner <http://example.org/1>

than this

_:LotR a bf:Instance ;
    bf:identifier _:bnode1
_:bnode1 a bf:Identifier
   bf:identifierType <http://id.loc.gov/vocabulary/identifiers/doi>
   bf:identifierValue "10.1000/182"
   bf:identifierAssigner <http://example.org/1>

I prefer the second as it associates properties of the identifier with the Identifier resource, namely its DOI-ness, rather than relying on the relationship between that particular Instance and the Identifier.  As above, what if there's a mismatch? Or what if another Instance has a relationship to that Identifier, like cites or references?
[Yes, it should cite the Work, not the Identifier, but I hope you see the point]

Perhaps it makes little difference and I'm splitting hairs.

No, I think it does make a big difference.

That said, one of the points you raised in the document was how, for example, an ISSN has a formal URN form and therefore could be represented as a URI (did not know that, so thanks).  Taking advantage of such a mechanism, I could see a scenario where the property bf:issn is defined as something like "ISSN for current resource in URN form" and reserved solely to allow something like this:

_:I1 a bf:Instance ;
    bf:issn <urn:ISSN:1560-1560> .

Yup, +1.  And bf:issn then isn't a subproperty of bf:identifier.
Otherwise it could be simplified to:

    <urn:ISSN:1560-1560> a bf:Instance .

modulo the trust issue discussed in the Authorities thread. 

while still allowing this:

_:I1 a bf:Instance ;
    bf:identifier _:bnode1

_:bnode1 a bf:Identifier
   bf:identifierType <http://id.loc.gov/vocabulary/identifiers/issn>
   bf:identifierValue "1560-1560"
   bf:identifierAssigner <http://example.org/issn/agency>

Agreed.  I see the point of Identifier for non URIs (including URN and URL as subsets of URI)

The immediately preceding two examples would establish a model whereby "bf:identifier" and "bf:Identifier" are used when capturing information about other, string-based identifiers while reserving the properties (bf:issn, bf:isbn10, etc) exclusively for URI-ified identifiers.  This aligns, I believe, more or less with your rule; I'm wondering if there is a way to refine when select properties are used and when they are not (providing there is merit to that idea).  I'm also looking at how they are defined.  Does that make sense?  Do you foresee issues with or benefits of allowing for this type of duplication?

Nope, other than the semantics of bf:issn in terms of the relationship between the subject and object.  If it's owl:sameAs, then the ISSN could be (again modulo the trust issue) the identifier for the Instance directly, rather than using a blank node and saying it's the same as a URI.
OK, I feel I rambled on a bit; I hope it was clear.

It is, thank you! 

All of it is to basically say that I think you raise a good point, but that I am trying to flesh it out some.  Thanks for taking the time to write it all down.

And for you to read and reply in such a considered fashion :)