Use a join for visualizing external information in mapfile

[Davelaar, Hilbert]

Hi list,
 
I want to visualize information stored in a DBF in my mapfile. The shapefile I am using has a code for each polygon which corresponds to a row in that DBF-file. Now I know how to physically join both so a column is added to the shapefile which a use in a expression to visualize the information. 
 
But a better solution for my situation that the information stays in the DBF-file, because this is the file thats updated all the time. I looked at the join-object, but that raises the question whether it is possible to define a join in my mapfile, and then use this join to visualize information from an external DBF-file?
 
So if have a polygon with code A1, and in the DBF is a code A1 together with a string 'Blue'. Is it possible then to say in the mapfile that 'Blue' has to be visualized with the color blue using an expression? And another thats defined as 'Green'. So when the external DBF-file is updated, and perhaps the color for code A1 changes to 'Green' then the visualization is also immediately updated using the link defined by the join?
 
Kind regards,
Hilbert Davelaar