SharePoint 2010 provides enhanced lookup functionality which is not available with SharePoint 2007 lookup fields. When creating a new lookup column type in SharePoint2010, site admin can set up some additional columns that can pull in multiple field values from the list that is being used as the lookup. Similar functionality can be achieved in SharePoint 2007 using Business Data column, but setting up Business Data column is not that user friendly or easy as Lookup columns.
Here is a screenshot of the configuration using a lookup column in Document Library:
When tagging/updating the metadata of documents or list items user will select only one tag and then additional columns are available in views and on view property pages.
Apart from the additional lookup fields, site admin can also enforce relationships so that it allows a cascade delete or restricts delete if a relationship still exists.
This feature is also new to SharePoint 2010. In SharePoint 2007 lookups, if anybody accidentally deletes the lookup value from the lookup list, all the lists and libraries where the lookup value is used are blanked out. Even admin doesn’t get a clue for the deleted metadata value until he/she finds it in Recycle Bin.
If there is a relationship associated with lookup and column, user cannot delete the lookup values from the lookup list. User get an error message when try to delete an item with relationship configured as Restrict delete.
