This function returns a unique 36-character string consisting of 32 alphanumeric, lower case characters and four hyphens. Format: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx (8-4-4-4-12 characters). Example: 123e4567-e89b-12d3-a456-426655440000. The function produces unique strings on each and every call, regardless of whether the call occurs within the same data mapper or not, or on concurrent threads.