Principles &
Patterns
Design Goals
Goals are non-negotiable.
· Correctness: The behavior of a system/component conforms to its specification (assuming the specification is correct).
· Efficiency: The system/component does not waste resources such as time and memory.
· Maintainability: Repairing or enhancing a system/component is not needlessly difficult.
· Security: The system/module prevents unauthorized or unintended use.
Design Principles
Principles usually help us achieve goals.
· Modularity: Systems should be built from cohesive, loosely coupled components (modules).
· Abstraction: The interface of a component should be independent of its implementation.
· Open-Closed: A component should be open to extension but closed to modification.
· Reusability: Components should be easy to reuse.
· Avoid mixed-Domain Coupling: Component in a more reusable layer shouldn't depend on components in less reusable layers:
Foundation components: String, Date, Number, etc.
Architectural components: Window, Menu, Dispatcher, etc.
Domain components: Policy, Employee, Shipper, Cart, etc.
Application Component: Controller, UserInterface, MenuListener, etc.
Metrics
A design metric measures the quality of a design.
Design Metrics (new)
Design Metrics (old)
Design Patterns
A design pattern is a well-designed, recurring collaboration.
A pattern catalog is an organized collection of design patterns.
A typical catalog entry has some form of the problem-solution format:
Name: The
name of this pattern
Problem: The common problem solved by this pattern
Solution: The common solution expressed as a template
Examples
References
Anti-Patterns &
Refactoring
An anti-pattern is a recurring design flaw. Usually the flaw violates one or more design principles.
Refactoring is a process that transforms poorly designed code into equivalent well-designed code.
Here are a few examples.
More can be found here: