DOCBOOK: Customizing the role attribute

I惴 trying to workout how to customize de role attribute for the
emphasis element.  First thing I would like to have
<emphasis role="bastardilla"> to render italics, and
<emphasis role="negrilla"> to render bold.

Then, perhaps having <emphasis> (with no role att.) to render
both bold and italics.  Other customization I want to achieve is
for having <emphasis role="color"> to render the especified
colour.

So far I扉e written this test.dsl file:

<!DOCTYPE style-sheet PUBLIC "-//James Clark//DTD DSSSL Style Sheet//EN" [
<!ENTITY docbook.dsl PUBLIC "-//Norman Walsh//DOCUMENT DocBook HTML Stylesheet//EN" CDATA DSSSL>
]>

<style-sheet>
<style-specification use="docbook">
<style-specification-body>

;; crear 愉ole愀 "bastardilla" y "negrilla"
;; tb crear uno para ambas

(element emphasis
  (if (equal? (attribute-string "role") "negrilla")
              (make sequence
	        font-weight: 'bold
		(process-children))
  (if (equal? (attribute-string "role") "bastardilla")
              (make sequence
	        font-posture: 'italic
		(process-children))
              (make sequence
	        font-posture: 'italic
		(process-children)))))

</style-specification-body>
</style-specification>
<external-specification id="docbook" document="docbook.dsl">
</style-sheet>

and run the following command line:

$ openjade -c /usr/local/share/sgml/docbook/dsssl/modular/catalog /
-c /usr/local/share/sgml/docbook/catalog /
-c /usr/local/share/sgml/openjade/catalog /
-d test.dsl -t sgml article.sgml

but I get no format at all.  Could you help me to understand how
to write stylesheets?

Thank You,
-- 
Horacio