Check out the new definitions that have just been posted:
The Data Access Layer - http://www.psdn.com/library/entry.jspa?externalID=1461&categoryID=110
Data Source Object - http://www.psdn.com/library/entry.jspa?externalID=1460&categoryID=110
and last, but certainly not least
Model View Controller Pattern - http://www.psdn.com/library/entry.jspa?externalID=1462&categoryID=107
Happy Reading!