Check Constraints within Data Modelling

[changeofhart]

I'm a relative newcomer to EA, so I apologise if this is a noddy request.
I am trying to set up a check constraint against an attribute in a table I have defined (ie, the usual 'Y'/'N' type constraint on a database column) but cannot see how to do it.

Any ideas?  

Thanks in advance for any help you can give me.
changeofhart