At 09:28 AM 1/7/2003 -0800, you wrote:
>Hi -
>
> I have been going over the XLink schema on the METS site, and I
>noticed that the role and arcrole attributes are defined
>
> <attribute name="role" type="string"/>
> <attribute name="arcrole" type="string"/>
>
>but in the XLink Spec (Version 1.0) you find the following in Section
>5.5:
>
> "The value of the role and arcrole attribute MUST be a URI
>reference ..."
>
> Am I misunderstanding something? Could someone please enlighten
>me?
It is true that the XLink spec states that both role and arcrole must
contain a URI.
However, it is also true that the XLink spec contains a non-normative DTD which
defines both role and arcrole attributes as type CDATA (since DTD's don't have
these little data typing niceties that XML schema have). In short, the DTD
promulgated
by the W3C gives you the room to violate what the spec says. In crafting
an XLink
schema, I basically took that as permission and precedent to do exactly the
same.
In short, it was intentional. I know that rigid conformance to the spec
would dictate
that these two attributes be typed as URIs. However, I'm certain that
there are plenty
of people out there who have taken advantage of the fact that role is
defined as CDATA
in the W3C DTD to put non-URI data into XLinks on the "we're only using
that information
locally anyway so why not" theory. The XLink schema available at the METS
web site
basically gives you the free to do what you want locally, including
violating the standard.
Since it doesn't *force* you to violate the standard (you can put a URI
into an xml attribute
typed as 'string'), it seemed an acceptable compromise. Anyone wanting to
enforce more
rigid adherence to the XLink standard is obviously free to craft their own
schema and
use it in place of the one provided by METS, and the METS schema
documentation is
pretty clear in stating that when you're filling in XLink attributes, you
should adhere
to the XLink spec.
If people think this is a big problem, I'd be happy to consult the board
about revising
the schema.
Jerome McDonough
Digital Library Development Team Leader
Elmer Bobst Library, New York University
70 Washington Square South, 8th Floor
New York, NY 10012
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(212) 998-2425
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