Class in Swimlane ????

[pjmvn]

Hi all.
I have a problem with swimlane, please help me.
I have this code:
First, this is OK, i have deploy this success without the class and xmlns, xsi tag, ....:

<process-definition
 name="DataBaseAccess">
 <start-state name="start process">
 <transition name="save to data base" to="save to database"></transition>
 </start-state>
 <swimlane name="nothing">
 <assignment expression="user(Every On)"></assignment>
 </swimlane>
..........

But when i include the schemas and no change this code, have an error in GPD of Eclipse(GPD v3.0.4).

<process-definition
 xmlns="http://jbpm.org/3/jpdl"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:schemaLocation="http://jbpm.org/3/jpdl http://jbpm.org/xsd/jpdl-3.0.xsd"
 name="DataBaseAccess">
 <start-state name="start process">
 <transition name="save to data base" to="save to database"></transition>
 </start-state>
 <swimlane name="nothing">
 <assignment expression="user(Every On)"></assignment>
 </swimlane>
.........

error:

cvc-complex-type.4: Attribute 'class' must appear on element 'assignment'.

Why i have this error when i have deployed success without the schemas ???
And are there any different in two way above ???
And what does "class tag" do???
Please give a sort example include java file is used with "class tag".
Thanks very much.

[aymanson]

Because the schema file set the attribute class as required.
you can add class="org.jbpm.identity.assignment.ExpressionAssignmentHandler" to prevent that.

The class tag allow you to delegate the assignment to your own class rather than using the expression provided by the jbpm identity model.