If you create only one alias from Date dimension in Physical Layer then you can get only one data either Ship Date or Order date details.
The data from Date dimension gets retrieved on the basis of the Join i.e on which key it was joined to the Fact.
To solve the above ambiguity you should create two separate alias tables in physical layer, hence you will have two logical tables in BMM Layer
Create Dim_Ship_Date and Dim_Order_Date from Date dimension.
And now, you can join the fact with these two aliases on different keys. This practice is usually followed.
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