There's a namespace for schema "stuff" in instances:

http://www.w3.org/2001/XMLSchema-instance

The prefix 'xsi' is typically used.

The attribute 'schemaLocation' specifies pairs of a namespace name and URL for location schemas.

Example:

<e:event xmlns:e="urn:publicid:IDN+cde.berkeley.edu:milowski:schemas:example-form:event:200402"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="urn:publicid:IDN+cde.berkeley.edu:milowski:schemas:example-form:event:200402 event.xsd">
...
</e:event>