How can I create Work Definition by parts using REST api?

Summary:

I want to create work definitions by parts, like header first, then operations, materials, etc. In document there is REST api for creating one work definition operation, but it needs the workDefinitionRequestsUniqID and workDefinitionHeadersUniqID which I can't find in the response from creating the work definiton.

/fscmRestApi/resources/11.13.18.05/workDefinitionRequests/{workDefinitionRequestsUniqID}/child/workDefinitionHeaders/{workDefinitionHeadersUniqID}/child/operations

Is it possible to create work definitions part by part, and where can I find these two IDs?