Oracle PL/SQL Programming, 5th Edition

Packages and Object Types

Packages are containers that allow you to group together data and code elements. Object types are containers that allow you to group together data and code elements. Do you need both? Do object types supersede packages, especially now that Oracle has added support for inheritance? When should you use a package and when should you use an object type? All very interesting and pertinent questions.

It is true that packages and object types share some features:

• Each can contain one or more programs and data structures.

• Each can (and usually does) consist of both a specification and a body.

There are, however, key differences between the two, including:

• An object type is a template for data; you can instantiate multiple object type instances (a.k.a. “objects”) from that template. Each one of those instances has associated with it all of the attributes (data) and methods (procedures and functions) from the template. These instances can be stored in the database. A package, on the other hand, is a one-off structure and, in a sense, a static object type: you cannot declare instances of it.

• Object types offer inheritance. That means that I can declare an object type to be “under” another type, and it inherits all the attributes and methods of that supertype. There is no concept of hierarchy or inheritance in packages. See Chapter 26 for lots more information about this.

• With packages, you can create private, hidden data and programs. This is not supported in object types, ...