A family of Microsoft relational database management systems designed for ease of use.
Take a look at the file NotInList.zip in my public databases folder at:
https://skydrive.live.com/?cid=44CC60D7FEA42912&id=44CC60D7FEA42912!169
You might have to copy the text of the link into your browser's address bar (not the link location). For some reason it doesn't always seem to work as a hyperlink.
This file demonstrates the use of the NotInlist event procedure of a combo box in various contexts, some which open a form to enter additional data to the new record in the referenced table, some which transparently insert a new row in to the referenced table where no additional data is required.