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You can define a hierarchy of Items. That is, you can say that an Item of one Type “contains” one or more Items of another Type. When dealing with DIDs, you might configure two Types in the system, “Circuit” and “DID’. You can then say that a Circuit can contain DIDs. A specific Circuit Item can be set to own one or more DID Items. Setting which Items own which other Items can be done manually but is really intended to be maintained automatically, typically via a Workflow.