$ReviewActivityClass = Get-SCSMClass -Name System.Workitem.Activity.ReviewActivity$
$ReviewerClass = Get-SCSMClass -Name System.Reviewer$
$ReviewActivityHasReviewer = Get-SCSMRelationshipClass -Name System.ReviewActivityHasReviewer$
$ReviewerIsUser = Get-SCSMRelationshipClass -Name System.ReviewerIsUser$