Base Commerce Classes and Interfaces
The base commerce interface implementations hold and manage other commerce interface implementations. For example, an Order interface implementation contains implementations of the CommerceItem, ShippingGroup, PaymentGroup, and Relationship interfaces. These interfaces define a mechanism for accessing the data stored in an object in a manner that frees it from the underlying implementation.

Address Classes
While not commerce-specific objects, the Address and ContactInfo classes play important roles in the purchase process.

Business Layer Classes
The business layer classes hold business logic for tasks like adding an item to an order, retrieving an order, adding shipping methods, and adding payment methods. These classes use the base commerce classes and the base commerce interfaces.

Pipelines
The purchase process pipelines execute a series of operations when called by the business layer classes.

Order Repository
The Order repository is the layer between Oracle ATG Web Commerce and the database server.