When creating a layered architecture, you'd separate your code (which is essentially text written in a chosen programming language) into separate layers based on its specific responsibilities, despite the fact that it's still just a series of text-based instructions. In order to create a program with layered architecture, you need to:

These steps will help you organize your program as a well-organized textual set of instructions that follows the layering principle

Dependency flow refers to the way components or layers in a software system interact and depend upon one another. The focus is primarily on design-time relationships rather than run-time behaviors. Basically, it goes like this:

At Design Time

• Layers and Directionality: Layers (e.g., UI and business logic) are dependent upon lower layers (e.g., data access and business logic). It prevents circular dependencies and ensures separation of concerns.
• Static Dependencies: Expressed through import statements, module references, and class associations, static dependencies describe explicit relationships

Define Layers

• Identify Core Functionality: Determine the essential functions of your system. These will likely form the core layers. Example: In a web application:Presentation Layer: Handles user interface (UI) and user interaction (e.g., HTML, CSS, JavaScript). Application Layer: Contains business logic, coordinates interactions between other layers, and manages application flow (e.g., controllers, services). Domain Layer: Represents core business objects and rules (e.g., entities, value objects, repositories). Infrastructure Layer: Provides supporting services like database access, messaging, and external integrations (e.g., database connectors, message queues).

2. Establish Clear Dependencies

• Unidirectional Flow: Layers should depend only on layers below them. This creates a clear hierarchy and reduces tight coupling. Example:Presentation Layer depends on Application Layer. Application Layer depends on Domain Layer. Domain Layer depends on Infrastructure Layer.

3. Define Interfaces and Contracts

• Abstract Interactions: Define interfaces between layers to specify how they interact with each other.
• Contract Enforcement: Ensure that all interactions adhere to the defined contracts. This improves maintainability and testability.

4. Implement and Test Layers Independently

• Modular Development: Develop and test each layer in isolation as much as possible.
• Mock Dependencies: Use mock objects to simulate the behavior of lower-level layers during testing.

5. Example with Python and Flask

Python

# app/__init__.py from flask import Flask from .controllers import main_bp app = Flask(__name__) app.register_blueprint(main_bp) # app/controllers/__init__.py from flask import Blueprint from .main import main_views main_bp = Blueprint('main', __name__) main_bp.add_url_rule('/', view_func=main_views.index, methods=['GET']) # app/controllers/main.py from flask import render_template from app.services import get_user_data def index(): user_data = get_user_data() return render_template('index.html', user_data=user_data) # app/services/__init__.py from app.repositories import UserRepository def get_user_data(): user_repo = UserRepository() user = user_repo.get_user_by_id(1) return user.to_dict() # app/repositories/__init__.py from app.models import User class UserRepository: def get_user_by_id(self, user_id): # Logic to fetch user data from database user = User(id=1, name="John Doe") return user # app/models/__init__.py class User: def __init__(self, id, name): self.id = id self.name = name def to_dict(self): return {'id': self.id, 'name': self.name}

Key Considerations:

• Trade-offs: Layered architecture can increase complexity. Carefully evaluate the benefits against the potential drawbacks for your specific project.
• Flexibility: Design your layers to be flexible and adaptable to future changes.
• Maintainability: Prioritize clear separation of concerns and well-defined interfaces to improve long-term maintainability.

Benefits of Layered Architecture

• Improved Maintainability: Changes in one layer have minimal impact on other layers.
• Increased Reusability: Components within a layer can be more easily reused in other parts of the system or even in other projects.
• Enhanced Testability: Layers can be tested independently, making it easier to identify and isolate bugs.
• Better Scalability: Layers can be scaled independently to meet changing performance requirements.