How to Link the interface attributes

Hi

Can you please let us know if a WebADI interface attribute can refer another attribute in the same interface?

For example:

If a WebADI interface has 2 columns:

P_START_DATE

P_END_DATE

Here I need to give a default value for P_END_DATE which is based on the P_START_DATE

So, in the interface setup I am selecting the 'Default Type' as 'SQL Query'. But I am not sure what to give in 'Default Value'

Something similar to: 'select : P_START_DATE from dual'

So, I want to know how an interface attribute can be referred in a default value(SQL query) of another attribute in the same interface