The problem with this kind of syntax: <activity type="mail"/> is that you can't define a schema anymore. The content type of the activity element has to allow any element. One solution is to use nested subelements: <activity> | <mail to='boss' /> | </activity> However, this is verbose and makes the process definition less readable. WS-BPEL solved this by having a number of stock activities like: <bpel:invoke operation="selfdestruct" /> and providing a placeholder for extension activities: <bpel:extensionActivity> | <jbpm:mail to='boss' /> | </bpel:extensionActivity> The BPEL approach may be worth considering here. @Heiko: the earlier posts were about skipping validation for user-defined extension items whose schema was unavailable. Just FYI. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4161629#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...