Creating a view on VBAK and VBAP

Dear ABAP/BW gurus,

This should be an easy question to answer.

I am trying to create a view on VBAK and VBAP through t-code SE11.

When I enter and highlight both VBAK and VBAP in the Table/Join Conditions tab and click on Relationships, the system says "No Relationships are defined for the tables". I can clearly see at SE11 that the tables are linked through VBELN.

Can you please tell me why the system says that there are no relationships between the two tables?

Thanks in advance