That is (still) incorrect.

A single schema may contain multiple namespaces, and there isn't a
unique identifier for a schema.  For example, any simple Dublin Core
based syntax must have at least two Namespaces, Dublin Core and the
wrapper element. SchemaLocation is not unique as there can be many
copies of the same schema.  A single schema may define multiple root
elements, such as MODS does with both item and collection level
elements.

Referring to your blog post, you can say how the four inter-relate:

Schema Identifier uniquely identifies the format.
Schema Location is a non-unique description of the format.
Schema Name is a short, human readable, non-unique name for the format
and Namespace is a non-unique namespace used by the format.

This is just a rehash of a previous discussion on this list, between us:

[log in to unmask]" target="_blank">http:[log in to unmask]

So I guess I'm wasting my time ;)

Rob Sanderson

On Thu, Feb 24, 2011 at 9:44 AM, Jakob Voss <[log in to unmask]> wrote:
> Hi,
>
> We are developing a general API management tool to provide different APIs
> (unAPI, SRU, OAI-PMH...) with different record formats (MARC, MODS, DC...)
> to our databases. We now stumbled upon some confusion regarding XML formats.
> The basic question is "what is a format and how do you refer to it?"
>
> I came to the conclusion that at least SRU schema identifiers are useless.
> In addition you can extract XML namespace URIs from XML Schemas, so all you
> need to identify a format is a link to its XML Schema.
>
> I wrote a more detailed blog posting about this at
> http://jakoblog.de/2011/02/24/xml-schema-vs-library-apis-oai-pmhsruunapi/
>
> Does anyone of you relies on SRU schema identifiers when consuming SRU?
> I think at least for XML-based formats we should only use the XML Schema as
> authoritative reference. Sure there are different applications of variants
> of one schema, but then it makes no sense to use global identifiers in
> addition to local names.
>
> Jakob
>
> --
> Jakob Voß <[log in to unmask]>, skype: nichtich
> Verbundzentrale des GBV (VZG) / Common Library Network
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>