The package specification is implemented by the package body. That is, the package body has the definition of every cursor and the subprogram declared in the package specification. Remember that the subprograms defined in the package body are available outside the package only if their specifications also show in the package specification. To match the subprogram specifications and bodies, the PL/SQL does a token-by-token comparison of their headers. Therefore, except for white space, the headers should match word for word. Or else, the PL/SQL raises an exception, as the illustration below shows:
CREATE PACKAGE emp_actions AS
PROCEDURE calc_bonus (date_hired emp.hiredate%TYPE, ...);
CREATE PACKAGE BODY emp_actions AS
PROCEDURE calc_bunus (date_hired DATE, ...) IS
-- parameter declaration raises an exception as 'DATE'
-- does not match 'emp.hiredate%TYPE' word for word
BEGIN ... END;
The package body can also contain the private declarations that define the types and items essential for the internal workings of the package. The scopes of these declarations are local to the package body. And hence, the declared types and items are unapproachable except from within the package body. Dissimilar the package specification, the declarative section of a package body can have the subprogram bodies.
The declarative section below of the package body is the optional initialization sections that typically hold the statements that initialize some of the variables formerly declared in the package.
The initialization section of the package plays a minor role as, dissimilar subprograms; the package cannot be called or passed parameters. As an outcome, the initialization section of the package is only run once, that is the first time you reference the package. Keep in mind that, if a package specification declares only constants, types, variables, exceptions, and call specifications, the package body is needless. Though, the body can still be used to initialize the items declared in the package specification.