Yes, you can.
When you edit your dw use menu View->Column specifications.
Place your validiation expresion and message (if you want to do it).
The validiation expresion you can build by your own, please check html help:
User's Guide/Working with Databases/Chapter 16.../Working with validation rules
Regards,
Zbyszek Zibi
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Zbyszek Ogledzki, email:zbyszek@pangea.com.pl