Items represent individual objects within each domain, and each item contains attributes with values. Each item is conceptually similar to a row in a spreadsheet. Items are distinguished by the presence of a unique ID, which can also be used when querying for a specific item.
This unique identifier is not automatically provided by SimpleDB, and is the responsibility of the developer.
A common scheme followed by users of SimpleDB is to generate Globally Unique Identifiers or GUIDs and use them as the key for each item. You are not required to use this scheme and are free to generate this ID anyway you like as long as it is unique. The ID also needs to be unique only within the domain of interest.
The February 24, 2010 announcement added ...