J2EE Design Patterns

Chapter 6. The Business Tier

The word “enterprise” has a long and storied association with business. Adam Smith used the word in The Wealth of Nations back in 1776, and the antecedents go back another century. So, it’s no wonder that when we talk about applications that support business processes we call them enterprise applications. The value of the application is bound up in the complexity of the business processes it represents, and in the amount of human effort the software removes from the equation. Virtually any large organization can benefit from properly deployed technology, from elementary schools to multinational corporations, and from volunteer groups to open source projects. In all of these situations, the value of the application depends on how well it supports the underlying business model.

This chapter introduces the business tier. We’ll talk briefly about business models and business tier components, and draw some distinctions between them. The patterns in this chapter cover the domain model, which defines the entities that interact within your system, and the business logic, which defines the different actions that can be performed on the domain model. Our primary focus is on flexibility and extensibility: patterns that make it easier to balance the performance requirements of today with the inevitable change requests of tomorrow.

Business tiers are about complexity, memory, and scale. Business tiers are complex because they implement the rules the business must follow. ...