How to delete a Contract detail and associated records?

We have CRM 2011 on premises. I am trying to cancel a contract detail without cancelling its parent contract.

Questions:

1) I found this code online:

TargetDeleteContractDetail target = new TargetDeleteContractDetail();
 target.EntityId = new Guid(someGuid);
DeleteRequest delete = new DeleteRequest();
 delete.Target = target;
 DeleteResponse deleted = (DeleteResponse)service.Execute(delete);

but TargetDeleteContractDetail is not coming up as a valid class.  In what namespace and in what dll does it reside?

2) Is there an alternate way of accomplishing this?

3) We have a custom entity, call it "D", which has an N:1 relationship with Contact.  D also has a relationship with a Contract Detail, call it "CD", as follows, where "X" is an entity that just connects the two.

When I cancel the contractdetail, I also have to delete all entity records X, that connect to all entity records D for that Contract Detail.

Please advise how to accomplish this.

Thank you.