(Note: this is addressed to METS with cc to MODS.)
A copy of the xlink schema is now at http://www.loc.gov/standards/xlink.xsd
It is identical to those at:
which are now identical to one another.
MODS will reference the new copy in its next version (3.2 - coming soon).
We recommend that METS also reference this new copy in its next version
This addresses a problem raised recently; when using the METS and MODS
schemas together there is a namespace conflict (same namespace, xlink, but
schema in two different places, won't validate).
(This problem remained unsolved for a few years because METS and MODS could
not reconcile different philosophies about the xlink namespace. But I now
notice that the two schemas are identical, I'm not sure when the METS xlink
schema was changed, but apparently the philosophies are reconciled.)
Instead of asking METS to reference xlink from the MODS directory, or asking
MODS to reference xlink from the METS directory, we have put a copy in a
"neutral" directory and recommend that xlink be referenced from that
directory. The existing METS and MODS xlink schema copies will remain where
they are, so that older MODS and METS instances won't be affected.