"There can only be one IDENTITY column per table"
Why is it so? Take a scenario of a vehicle, there exists a chasis number which is unique as well as the registration number which turns out to be unique. To depict this scenario in sql server we need a custom implementation for on of the columns. Conversely, in Oracle you can have as many sequences as you want on a table. Why is there a restriction on the IDENTITY Column, any specific reasons?
The scenario of having a vehicle schema is something imaginary am questioning myself as to why there's a restriction on the identity column.