Google Base is a database in Google's cloud.
A Google Merchant Center account is used to submit items to Google Shopping. Currently, items submitted to Google Product Search (Google Shopping), if processed correctly, reside partly within Google Base. At some point during processing, valid products items are indexed for use in Google Product Search; otherwise, items may not be indexed for Google Shopping and remain within Google Base -- due to a variety of policy or rules issues.
The view within Google Base is the raw XML data used to display and format comparison-shopping information. The raw data view within Google can be important in determining many issues with a merchant's products -- anything from why a product image isn't displaying, to why an item fails to be indexed, to why particular text (an attribute's value) displays oddly, to how a merchant's competitors might be gaining in rank or position. A current beta release of Celebird-Gbase can be found here:
http://www.celebird.com/cloud/celebird-gbase.htm
Simply, Celebird-Gbase allows merchants using a Google Merchant Center account or anyone using a Google Base account to search and verify submitted item information.