What kind of data feed? For platforms like Google Shopping, Amazon etc. the most common method is to use a 3rd party tool that works with your shopping cart.

Like kjamesnv said - there are apps that integrate with almost every shopping cart that will automatically create and submit your datafeeds daily to any shopping engine that you want.

What eCommerce platform are you using?

Just be a bit careful with datafeeds. It's really useful to import products. But you'll need your own content, descriptions if you want to try and compete. Google will generally favour the original publisher, so you'll need to work hard to over come that.