Thanks, Mikael, as usual, your explanations are quite clear. This makes sense although my last question regarding how to infer this result from the documentation remains.
I hope you do not mind if I press the example a bit further. Setting aside the wisdom of having a property with "both allowed", it does happen. For example, a project I am working on wants to make it possible to include "subjects" in a form I might call 'keywords' (free text--i.e., no URI) AND/OR terms drawn from specific VES (some VES with Value URI and some others with VES URI and no Value URI). And, let's assume, that we intend those keywords to be legitimate literals in terms of the Abstract Model as you just described, Mikael. Now, (unfortunately?) the scenario I just described is not a case of "no further constraining". When it comes to the VES, there are several constraints. In such a case, how can I represent this in a DSP? Am I talking about two separate statements representing subject (one literal and another nonliteral with VES constraints)? With DC creator in your example, Mikael, a similar scenario might be handled by using both the dc:creator (for literal) and dcterms:creator (for nonliteral) if I wanted data that modeled true to the Abstract Model. But I do not seem to have the same luxury with dc:subject/dcterms:subject. Or do I? Or have I again wandered off base? Or is my scenario absolutely untenable?
Getting this straight makes a big difference for me since, in the end, a technical implementer is going to inherit an XML or RDF/XML representation of this DSP and should be able to determine appropriate behavior in configuring my scenario in a metadata generation tool...or so I would think.
Again, thanks, Mikael for your quick response.
Stuart
-----Original Message-----
From: DCMI Architecture Forum [mailto:[log in to unmask]] On Behalf Of Mikael Nilsson
Sent: Monday, August 31, 2009 6:48 AM
To: [log in to unmask]
Subject: Re: DSP statement template "type" constraint question
Hi Stuart!
There are obviously some unclear parts of the documentation. I believe
the intended meaning is well-defined, even though the text is not
perfect. Let me try to sort it out:
sön 2009-08-30 klockan 17:47 -0700 skrev Stuart Sutton:
> I am trying to wrap my head around the DSP statement template "type"
> constraint. According to the specification at section 6.3, permitted
> values are "literal" or "nonliteral" with the default being "both
> allowed".[1] It further states that "[i]f no value is given, no
> further constraining on the value surrogate can be made." So, here is
> my question...are "no further constraining on the value surrogate" and
> "both allowed" equivalent?
Yes. The language is intended to convey the fact that the default value
"both allowed" cannot actually be explicitly set - it is only achieved
by not setting a value at all for that attribute. Maybe that is not a
very good idea, but that's what the current text is supposed to say.
> If so, what is the *USEFUL* result of a statement in a DSP that uses
> the type default and, therefore, has no value surrogate constraints?
The result is that absolutely anything goes. (With the caveat that a
related description of the value in the Statement might be invalid due
to other contraints). Whether that is useful or not... well, that
depends on what you're doing.
> Is a system consuming the DSP with such a statement type default to
> assume that it is dealing with the equivalent of a non-literal where
> every possible variation is optional--optional Value URI, optional VES
> URI, optional 0-n Value strings, optional language designations, and
> optional SES URI?
No. It might also be a literal value.
> Is that what "no further constraint" means? Or is such system
> consuming the DSP with a statement default type declaration simply
> intended to stare back at me asking "what do you want"? (And,
> further, what does "further" mean?)
"further" in the text refers to the fact that you're not allowed to add
any Literal value constraints or Non-literal value constraints to the
Statement Template. You ARE allowed to add property constraints and
occurence constraints on the Statement, though.
>
> I come to this question because I am working on a DSP that has a
> statement where the desired result is that "both [are] allowed". Now,
> it seems to me that if I want "both allowed" and I take the
> specification of the Abstract Model literally, all I need to do is set
> the statement type as "nonliteral" and make all the component parts of
> that non-literal "optional".
No. That would not give you the option of using a literal value.
> The Abstract Model defines a nonliteral as follows: "A nonliteral
> value surrogate is a value surrogate for a non-literal value, and is
> made up of zero or one value URI (a URI that identifies the
> non-literal value associated with the property), zero or one
> vocabulary encoding scheme URI (a URI that identifies the vocabulary
> encoding scheme of which the non-literal value is a member), and zero
> or more value strings. Each value string is a literal which represents
> the non-literal value."[2] So, it appears that everything in a
> nonliteral is optional (i.e., "zero or more"). As a result, I can
> express the equivalent of a literal value using a nonliteral where I
> optionally do not use either a Value URI or VES URI. And, of course,
> for a pure literal, I'd need to limit my value to one value string.
It's true that you can express "the equivalent" of a literal value using
a non-literal and a single value string. Though the contained amount of
information is the same, the semantics are very different which is
evident from the RDF representation of the two cases.
This is the non-literal case (using only resources without URIs)
_:book dcterms:creator _:adam
_:adam rdf:value "Adam Taylor"
while this is the literal case
_:book dcterms:creator "Adam Taylor"
It was an explicit requirement on the DSP spec to be able to distinguish
between these two cases, declaring one valid and the other invalid. The
second form actually IS invalid according to the semantics of
dcterms:creator, which is defined with values in the class of Agents.
The string "Adam Taylor" is not an Agent.
Thus, while from a certain application's point of view the two contain
the same information, from another application's POV they are very
different. For example, an application that wants to add a statement
about the email address of the author can do so only in one of the cases
(the first).
It boils down to the fact that in DCAM, a "literal value" is NOT the
same thing as a "value string".
A "literal value" IS the value, while a "value string" only REPRESENTS
the value, and in a vague sense too.
>
> So, it seems to me that if I truly want "both" enabled, setting the
> statement type to "nonliteral" and making all components of that
> nonliteral functionally "optional" explicitly enables at least all of
> the following value patterns (in other words, "both"):
>
> PATTERN #1:
> Value URI (only) (e.g., http://purl.org/dc/dcmitype/Collection)
>
> PATTERN #2:
> Value URI + VES URI (e.g., http://purl.org/dc/dcmitype/Collection +
> http://purl.org/dc/terms/DCMIType)
>
> PATTERN #3:
> Value URI + Value string (e.g., http://purl.org/dc/dcmitype/Collection
> + "Collection")
>
> PATTERN #4: VES URI + Value string (e.g.,
> http://purl.org/dc/terms/DCMIType + "Collection")
>
> PATTERN #5: Value string only ("Collection")
>
> PATTERN #6: Value string + language designation (e.g., "Collection" +
> en (or, if appropriate, an SES))
Yes, this is all true. But you're missing pattern #7: Literal value.
>
> While there may be other rational (or irrational) patterns possible,
> these seem to me to exhaust the patterns for what the Abstract Model
> permits for "both" literal and nonliteral value surrogates.
>
> Now, I have been on the planet long enough to know that I am probably
> messed up! So, please straighten me out. How would one explicitly
> declare a statement with a type that is "both" without relying on the
> ill-defined default. And, if relying on the default is the key, then
> how exactly are we to infer as much reliably from the DSP and Abstract
> Model documentation as they stand.
I'm not sure how to answer that last question, but I would be happy to
hear any suggestions for improvement of the DSP text.
And, thanks for the interesting feedback!
/Mikael
>
> Stuart
>
>
> [1] http://dublincore.org/documents/2008/03/31/dc-dsp/
> [2] http://dublincore.org/documents/2007/06/04/abstract-model/#sect-2.2
>
> Associate Professor & Chair,
> MLIS Degree Program
> The Information School
> Mary Gates Hall, Suite 370
> Box: 352840
> University of Washington
> Seattle, WA 98195-2840
> Tel. 206-685-6618
>
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