Google Base has made an update that from reading the blog post and email sounded like requirements for each item. They have added UPC, MPN (Manufacturer Part Number) and ISBN to the list of attributes for Google Base submissions. Google says:

“We recently added UPC, MPN and ISBN to the [...]

It’s been a little while since our last entry into the blog. Since we launched FeedPerfect on March 1, we have been busy working with customers and on new features and additional channels. We started on March 1st offering service to 6 channels; Google Product Search, Shopzilla, Shopping.Com, Yahoo! Shopping, [...]