Schema help

Hello All,

       I am developing XML schema for my application. I struck up
while writing XSD. Please can any body help.

My requriment is :
   We have to support diffirent type of task. Each task is in XML
format. I have a tag called type and parameter type as a elements in
XSD. If task type is type1, only subset of parameters type I have
support. If task type is type2, only subset of parameters type I have
support. Parameters type is global tag - contains all the parameter
types for all tasks. My question is
if ( task type = 'type1' )
{
 parameter type 1
 parameter type 2
}
else if ( task type = 'type2' )
{
 parameter type 2
 parameter type 3
}
else if ( task type = 'type3' )
{
  parameter type1
  parameter type2
  parameter type3
  parameter type4.
}

  How to specify this code in XSD ?


Thanks and Regards,
Chandu