Answer.

Layered Architecture is a classic way of organizing IT systems where the application is structured into a set of layers, each of which implements a separate level of abstraction: user interface, business logic, data access, and infrastructure mechanisms. Typically, the Presentation Layer (UI), Business Logic Layer, Data Access Layer, and Data Layer are distinguished.

Each layer interacts only with its adjacent layers, which promotes modularity and simplifies code maintenance. This approach makes it easy to test individual parts of the system and conduct refactoring.

Example code (Layered Architecture in Python):

# Data Layer
class UserRepository:
    def get_user(self, user_id):
        # Get user from the database
        pass

# Business Logic Layer
class UserService:
    def __init__(self, repo):
        self.repo = repo
    def get_user_profile(self, user_id):
        user = self.repo.get_user(user_id)
        # Business logic
        return user

# Presentation Layer
class UserController:
    def __init__(self, service):
        self.service = service
    def get(self, user_id):
        user_profile = self.service.get_user_profile(user_id)
        return user_profile

Key features:

• Provides clear separation of responsibilities between the system layers.
• Simplifies the support and testing of individual components.
• Can lead to excessive dependencies between layers if isolation is not strict enough.

Trap Questions.

Is it permissible to access a lower layer directly from the upper layer, bypassing intermediate ones?

No, according to the principles of layered architecture, each layer interacts only with the layer directly beneath it. Violating this principle leads to tight coupling and deteriorates maintainability.

Is it true that layered architecture does not scale well?

Not always. Scaling is possible but may be more complex compared to microservices. Horizontal scaling of individual layers (e.g., backend services) is standard practice.

Can one layer implement logic that pertains to multiple layers at once?

Ideally — no. Cross-cutting business logic leads to confusion and complicates maintenance. Functions and classes should reside at the appropriate layer.