A single declaration of a symbol as it is used in
  the source code.  An occurrence can be any language
  construct, such as a variable, a routine, or a
  constant.  SCA determines which occurrences belong to
  a particular symbol based on the rules of the language
  in use.  It does not matter whether all occurrences are
  in the same module or spread over several modules.  All
  occurrences still belong to the same symbol.