Packages

A package is a schema object that groups logically related PL/SQL types, variables, and subprograms. Packages usually have two parts, a specification (called the spec) and a body; sometimes the body is unnecessary. The specification is the interface to the package. It declares the types, variables, constants, exceptions, cursors, and subprograms that can be referenced from outside of the package. The body defines the queries for the cursors and the code for the subprograms.

You can think of the specification as an interface and the body as a black box. You can debug, enhance, or replace a package body without changing the package specification.

The specification holds public declarations, which are visible to stored procedures and other code outside of the package. You must declare subprograms at the end of the specification.

The package body holds implementation details and private declarations, which are hidden from code outside of the package. Following the declarative part of the package body is the optional initialization part, which holds statements that initialize package variables and do any other one-time setup steps.

Applications that call the subprograms in a package only need to know the names and parameters from the package specification. You can change the implementation details inside the package body without affecting the calling applications.