This discussion would be more meaningful on the METS listserv. MODS implemented xs:id essentially because that’s what METS requested, because they reference elements via xs:idref. That's a METS design choice.  --Ray

> -----Original Message-----
> From: Metadata Object Description Schema List
> [mailto:[log in to unmask]] On Behalf Of Saašha Metsärantala
> Sent: Monday, March 28, 2011 9:19 AM
> To: [log in to unmask]
> Subject: Re: [MODS] draft MADS 2.0 schema ready for community review
> and testing
> 
> Hello!
> 
> > > I also wonder why not use xml:id
> > > instead of MADS's own ID.
> > It's not MAD's own ID, it's xs:id.
> I had noticed that the type of MADS' @ID was xs:ID, and it is the
> reason why I suggested the use of @xml:id.
> 
> > record when it is encapsulated
> > within a wrapper record,
> It seems that this problem could be better solved with xs:keyref and
> xs:key (these are a totally different things than xsl:key) which offers
> a flexibility unavailable with xs:IDREF and xs:ID together. In
> "ID/IDREF Versus xs:key/xs:keyref" pp. 149-150 in the book "XML Schema",
> Eric van der Vlist explains that quite well.
> 
> I mean that the usefulness of the type xs:ID is mainly both in the past
> and in the future. At the time when @xml:id was not yet available, ID's
> could only be expressed with the type xs:ID on a local element. In XML
> Schema 1.1, several attributes (with different names) will probably be
> allowed to have the type xs:ID even when these attributes are placed on
> the same element in an instance document, and therefore, xml:id will
> not be enough as an attribute name for attributes of type xs:ID. But
> XML Schema 1.1 is not (yet) a W3C recommendation.
> 
> Regards!
> 
> Saašha,