There are various ways to design this. From a high altitude, think about whether you want the user screen to periodically poll to see if there is new data, or if you want it to have an asynch listener channel open that is notified when new data is available. Also, start thinking about any out-of-box screens you can think of where the screens already update automatically, and take a look at how they work, to get ideas. /Eric
In Pega 7, you can configure "Refresh condition" on a section include/dynamic layout to achieve this sort of requirement.
Refer to pzExplorers OOTB section. Refresh condition is configured to auto refresh the Recent Explorer.
In your case if this auto refresh has to happen for all users, then having node level data page that gets updated whenever agent fetches fresh data from external database, and then using this node level data page 'Refresh condition' have to be configured on section that needs auto refresh.