10. Object Identity

• Identity is defined by the set of characteristics that distinguish particular object instance
  from other objects of the same type.

• Name of the object is not equivalent to its identity.

  • (The names are involved in mechanisms of overloading/aliasing, names can be re-defined in nested scopes... among other things specific to a particular programming language.)

• The most common incarnations of object's identity are:

  • reference to the object instance in memory

  • set of unique values of primary keys

  • message digest (authenticator).

    • (Obtained by calling a deterministic procedure (often a cryptographic hash function) that takes an arbitrary block of data and returns a (presumably unique) fixed-size bit string, known as the hash value, or digest.)