update or synchronize

Hi,

I'm starting to use vdata a lot. so far, i'm very satisfied

I'm a bit unsure of the difference in the profile setting between update and synchronize (see picture)

can you tell me exactly what both do? Is synchronize a bidirectionnal update (how does it work). I didn't found specific information in your well written documentation.

Basically, I maintain data in csv files and I want these data to be replicated in the website data tables. What is the correct setting for me?