In Go callers specify interface. It is lower level packages' responsibility to conform to high level interfaces.
- responsible for middleware
- encoding, writing out
Business here refers to the layer that provides value to consumers
- returns: serializable structs
- expects: models from data
model has the interfaces that business layer expects
- returns: models
- type definitions in this layer are decoupled from those in business layer
- inmemory package: fake in memory data
- nosql package: meant to connect to database
both will be able to fulfil interfaces required by business layer, but underlying implementation / structural details are encapsulated.