Adding a Relationship to a Group of a Imported Management Pack using PowerShell

Question

I want to add a relationship to a existing group in SCOM so that more types of object can be added to the group. How to do this? I've managed to do this but don't know how to specify the "containment" relation in powershell. Please advise. Thanks!
P.S. The to be answered line is "$relationshipClass.Base = ???"
$ManagementServer = "localhost"
$ManagementPackID = "TestNewVerTemplate"
$ReName = "Test_22"
Add-PSSnapin Microsoft.EnterpriseManagement.OperationsManager.Client
$MG = New-Object Microsoft.EnterpriseManagement.ManagementGroup($ManagementServer)
$MP = $MG.GetManagementPacks($ManagementPackID)[0]
$relationshipClass = New-OBject Microsoft.EnterpriseManagement.Configuration.ManagementPackRelationship($MP, $ReName, [Microsoft.EnterpriseManagement.Configuration.ManagementPackAccessibility]::Internal);
$sourceClass = Get-SCOMClass -Name "GroupPopulation.TestNewVerTemplateGroup"
$targetClass = Get-SCOMClass -NAme "Microsoft.Windows.Computer"
$relationshipClass.Abstract = $false;
$relationshipClass.Base = ???
# There is some existing relationship in the group. If it is used, then the script works.
# $relationshipClass.Base = $MP.GetRelationships()[0].Base;
$relationshipClass.DisplayName = "sample relationship";
$relationshipClass.Description = "sample relationship";
$source = new-object Microsoft.EnterpriseManagement.Configuration.ManagementPackRelationshipEndpoint($relationshipClass, "Source");
$source.Type = [Microsoft.EnterpriseManagement.Configuration.ManagementPackElementReference`1[Microsoft.EnterpriseManagement.Configuration.ManagementPackClass]]::op_implicit($sourceCLass);
#$source.Type = $MP.GetRelationships()[0].Source.Type;
$relationshipClass.Source = $source;
$target = new-object Microsoft.EnterpriseManagement.Configuration.ManagementPackRelationshipEndpoint($relationshipClass, "Target");
$target.Type = [Microsoft.EnterpriseManagement.Configuration.ManagementPackElementReference`1[Microsoft.EnterpriseManagement.Configuration.ManagementPackClass]]::op_implicit($targetClass);
#$target.Type = $MP.GetRelationships()[1].Target.Type;
$relationshipClass.Target = $target;
$mp.Verify();
$mp.AcceptChanges();

Answer 1

Amdishigh,
Please check if any of the following articles (I have 2 depending on your opsmgr version) apply to your environment.
for SCOM 2007:
http://msdn.microsoft.com/en-us/library/bb437513.aspx
for SCOM 2012:
http://msdn.microsoft.com/en-us/library/hh328983.aspx
hth,
Jose