Hi,
As far as I know there are no examples or guidance of how to connect or update a back-end database in the __Prism__, I believe this is mainly because this guidance is focused on the presentation layer and not how you architect your Business Logic Layer or Data Access Layer. And this is why there are no Quick starts related to this. However, if you believe this should be changed, you could copy this as a work-item in the issue tracker section , so the P&P team can analyze this for future releases.
On the other hand, I believe you could check some of the samples suggested in this thread where a similar topic was discussed, perhaps you could find them useful to tackle your scenario:
Additionally, you may also find the new upcoming release from the P&P team named Kona interesting, although it is in its first drops, it will will provide written guidance and a reference implementation that describe recommended practices for building LOB Windows 8 client apps using WinRT and .NET.
Best Regards,
Agustin Adami
http://blogs.southworks.net/aadami