"A subsystem is a set of classes collaborating to fulfill a set of responsibilities. Although subsystems do not exist as the software executes, they are useful conceptual entities."

“Experienced object designers explore the design space from many different angles. They refine ideas of how their system should respond while they are in the middle of building and discarding ideas about how their design should work. Getting a design to gel involves making assumptions, seeing how they play out, changing one’s mind or perspective slightly and re-iterating. Design is a difficult, involved task. It inherently is a non-linear process. Yet, we are asked to trace our design results back to system requirements. And, if we uncover some implications during design, we’d like to tune our system requirements to reflect necessary design compromises.”

“Users can work with analysts and object designers to formulate and tune system requirements. People from business, analytical and object design disciplines can come together, learn from each other and generate meaningful descriptions of systems that are to be built. Each participant and each project has slightly different concerns and needs. Practical application of use cases can go a long way to improve our ability to deliver just what the customer ordered.”

“The goal of is to improve encapsulation. It does so by viewing a program in terms of the client/server model.”

“Frameworks are white boxes to those that make use of them. Application developers must be able to quickly understand the structure of a framework, and how to write code that will fit into the framework. Frameworks are reusable designs as well as reusable code.”

“Responsibility-driven design specifies object behavior before object structure and other implementation considerations are determined. We have found that it minimizes the rework required for major design changes.”

“Frameworks are skeletal structures of programs that must be fleshed out to build a complete application. For example, a windowing system or a simulation system can both be viewed as frameworks fleshed out by a windowed application or a simulation, respectively.”