How can I access another class in a MembershipRule's Expression

Question

Hello,
I want to create an InstanceGroup using Module Microsoft.SystemCenter.GroupPopulator.
I need to collect all Logical Disks which contain an MS SQL DB Log File.
I would start as follows:
<DataSource ID="DS" TypeID="SC!Microsoft.SystemCenter.GroupPopulator">
  <RuleId>$MPElement$</RuleId>
  <GroupInstanceId>$Target/Id$</GroupInstanceId>
  <MembershipRules>
    <MembershipRule>
      <MonitoringClass>$MPElement[Name="Windows!Microsoft.Windows.LogicalDisk"]$</MonitoringClass>
      <RelationshipClass>$MPElement[Name="MSIL!Microsoft.SystemCenter.InstanceGroupContainsEntities"]$</RelationshipClass>     
<Expression>
        <And>
  <!--
   First Expression
  -->
          <Expression>
            <SimpleExpression>
              <ValueExpression>
                <Property>$MPElement[Name="Windows!Microsoft.Windows.LogicalDevice"]/Name$</Property>
              </ValueExpression>
              <Operator>Equal</Operator>
              <ValueExpression>
  <!--
    How can I access another class's properties ? 
  -->
                <GenericProperty>$MPElement[Name="SQL!Microsoft.SQLServer.2008.DBLogFile"]/Drive$</GenericProperty>
              </ValueExpression>
            </SimpleExpression>
          </Expression>
          <Expression>
            <SimpleExpression>
              <ValueExpression>
                <HostProperty>
                  <MonitoringClass>$MPElement[Name="Windows!Microsoft.Windows.Computer"]</MonitoringClass>
                  <Property>PrincipalName</Property>
                </HostProperty>
              </ValueExpression>
              <Operator>Equal</Operator>
              <ValueExpression>
                <GenericProperty>$MPElement[Name="SQL!Microsoft.SQLServer.2008.DBLogFile"]/Drive$</GenericProperty>
              </ValueExpression>
            </SimpleExpression>
          </Expression>
        </And>
      </Expression>
    </MembershipRule>
  </MembershipRules>
</DataSource>
In the first expression you "see" my question:
I want to compare the LogicalDisk's Name Property with the DB Log File's Drive property.
But how can I access the DB Log File's Drive property in this MembershipRule ?
Furthermore LogicalDisk and DB Log File must be hosted on the same Windows Computer.
Would be great if somebody could help.
Thanks
Sebastian

Answer 1

Hi Niki,
thanks for the idea, but that will not work. $Target/Id$ refers always to the group to be discovered.
On last week end I was given following idea, hope it will work:
Step 1
Collect all the DB SQL Logfile Objects and write computername (PrincipalName?) and Driveletter into a textfile, line by line. Shouldn't be a problem, PowerShell is your friend.
Step 2
Read the file from Step 1, build discovery data for each disk drive as object of class "Logical Disk (Server)",
and then discover the containment-relationships from those Logical Drive(Server) Objects to the InstanceGroup.
Perhaps I must do it for the OS-Version related Disks, because I need the target classes  of the Logical Disk Freespace monitors. Some more work. "Risks": I donot know the discovery algorithm for the Logical Disk(Server) Objects, but a "deep
dive" into the MPs should help.
Thanks to all, who have read.
I will inform you about progress and success
sebastian