Universally Unique Identifier

UUID is Universally Unique Identifier, also known as a GUID (Globally Unique Identifier) in Windows. UUIDs are long, random numbers that are pretty much guaranteed to be unique. They are recommended for database primary keys in distributed databases, where records may have to be inserted when offline.

A UUID is a 16-byte (128-bit) number. The number of theoretically possible UUIDs is therefore about 3 × 1038. In its canonical form, a UUID consists of 32 hexadecimal digits, displayed in 5 groups separated by hyphens, in the form  for a total of 36 characters (32 digits and 4 hyphens). For example:

Discussions

 * Advantages and disadvantages of GUID / UUID database keys - Stack Overflow
 * Primary Keys: IDs versus GUIDs - Coding Horror
 * What’s your opinion on using UUIDs as database row identifiers, particularly in web apps? - Stack Overflow
 * What should I choose for my primary key? - ASP FAQ