You can use your Internet domain name as the owner identifier:

urn:publicid:IDN+cde.berkeley.edu:...

Separate segments by colons (':')

urn:publicid:IDN+cde.berkeley.edu:schema:coursedoc:slides:

Add some version information:

urn:publicid:IDN+cde.berkeley.edu:schema:coursedoc:slides:200403

Maybe some language/locale information

urn:publicid:IDN+cde.berkeley.edu:schema:coursedoc:slides:200403:en

Note that spaces are encoded as '+' as spaces aren't allowed in URI values.