1. What are layers

  • Abstraction layers

  • Single responsibiility

  • isolate roles and skills

  • multiple implementations

  • Classic 3-lyaer

  • User Interface

  • Business Layer

  • Data Access layer

  • Modern 4-layer architecture

image-20211121220111431

  • Variations
  • Multiple UI
  • Add web service layer etc.

1. Application Layer

  • Knows about domain layer.

  • No idea oabout presentation, persistnace or infrastructure

  • Dependency inversion

  • Abstractions should not depend on details
  • Rather, details should depend on abstractions

image-20211121221357141

Demo