The presentation layer in the three-tier architecture uses MVC, so can the interface in the business logic layer not be directly called from the outside? Instead, it should interact with the business logic layer through the Controller in MVC. Only the Controller of the presentation layer can be called externally?
In other words, only the Controller in the presentation layer MVC is allowed to interact with the business logic layer (BLL)?
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Yes, the BLL layer can only be called by the controller. If you want to call it externally, you can call it through WebApi.
The business logic layer can only be called by the controller, which is correct.