Five attributes of a complex system

Hierarchical structure
architecture of a complex system is a function of its components as well as the hierarchical relationships among these components.
Relative Primitives
The choice of what components in a system are primitive is relatively arbitrary and is largely up to the discretion of the observer of the system.
Separation of Concerns
separating a computer program into distinct sections such that each section addresses a separate concern.
A concern : a set of information that affects the code of a computer program.
Makes it possible to study each part in relative isolation.
Common patterns
complex systems have common patterns. These patterns may involve the reuse of smaller components,
E.g cells found in both plants and animals.
Stable intermediate forms
complex systems tend to evolve进化 over time.
A complex system that works usually evolves from a simple system that worked.
As systems evolve, objects that were once considered complex become the primitive objects on which more complex systems are built

Bringing order to the chaos: Object Oriented Design and Programming

OOP
Object-oriented programming is a method of implementation执行 in which programs are organized as cooperative collections of objects, each of which represents an instance of some class, and whose classes are all members of a hierarchy of classes united via inheritance relationships.
OOD
Object-oriented design is a method of design encompassing围绕 the process of object-oriented decomposition分解 and a notation记号 for depicting描述 both logical and physical as well as static and dynamic models of the system under design.