Tài liệu PL/SQL User’s Guide and Reference phần 6

What Is a Package?
A package is a schema object that groups logically related PL/SQL types, items, and
subprograms. Packages usually have two parts, a specification and a body, although
sometimes the body is unnecessary. The specification (spec for short) is the interface
to your applications; it declares the types, variables, constants, exceptions, cursors,
and subprograms available for use. The body fully defines cursors and subprograms,
and so implements the spec.
As Figure 8–1 shows, you can think of the spec as an operational interface and of
the body as a black box. You can debug, enhance, or replace a package body
without changing the interface (package spec) to the package.