Including processes that are external to the system in Use Case diagram and DFD

Question

I am designing a system with several diagram for a project. I am trying to summarize my question with 2 simple diagram which can demonstrate my doubt. Below are my use case diagram and a context diagram.
Use Case Diagram

Context Diagram

What my question is.., from both of the above diagram (1) Request Quotation and (2) Accept Quotation are two processes which are communicated verbally (not through the system). To explain, if a customer requires a quotation, he approaches the sales manager and ask for the quotation verbally. Similarly, if customer is willing to go forward, he accept the quotation verbally by approaching the sales manager by mail or phone.
When those 2 process have nothing to do with the internal system, do I really need to include them in the above diagrams? In case if I eliminate them both, I will lose the Actor (Customer) completely from the Use Case diagram. Is it acceptable.
Please explain me the best approach to follow here.

Christophe · Accepted Answer

The key to answer is to define correctly the scope of your diagram.  In the case of the use-case, it's a bout the subject, i.e. the system under consideration:

If the system considered is the organisation dealing with the customer,  request and accept quotation would be on the diagram,  because the employee handling the oral conversation is part of the organisation that is modelled.

If the system is the IT solution, the you shall only show the actors of that solution, i.e. the employee interacting with the software, but not the customer if there's no direct interaction, because it would be misleading.

There is no context diagram in UML.  This is data-flow diagram language (DFD).  Nevertheless, the principles should be exactly the same.

Including processes that are external to the system in Use Case diagram and DFD

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