• why
• what
• how

properties of a true high-level language

• Elegance: there is a simple, easily understood relationship between
  the notation used by a high-level language and the concepts
  expressed.
• Abstraction: each expression in a high-level language describes one
  and only one concept. Concepts may be described independently and
  combined freely.
• Power: with a high-level language, any precise and complete
  description of the desired behavior of a program may be expressed
  straightforwardly in that language.

design principle

• SoC: separation of concerns :: mudularity

• abstract

• indirection
  > All problems in computer science can be solved by another level of indirection, except for the problem of too many layers of indirection.

character

• cache
  • cache,
  • 内存页
  • DNS缓存，
• concurrent