The BNF for a query has:
<sort specification> ::= <column name> [ ASC | DESC ]

However if we want to allow queries with JOINs to order their results, like:
SELECT B.cmis:ObjectId, B.dc:title FROM cmis:Document A JOIN cmis:Document B ON A.cmis:ObjectId = B.my:field WHERE A.dc:description = 'foo' ORDER BY B.dc:title

Then we have to use a BNF like:
<sort specification> ::= <column reference> [ ASC | DESC ]

Note: In this BNF statement, SQL-92 has <column name>, but SQL 2008 actually has a very generic <value expression> instead. I think <column reference> is sufficient for CMIS.