Layered Architecture

Layered architecture is a software architectural pattern that organizes applications into separate layers or tiers, each having distinct responsibilities and functions. This style is also known as the n-tier architecture, where 'n' denotes the number of layers involved.

Here are the commonly included layers in this type of architecture:

1. Presentation Layer: Also known as the User Interface Layer. This layer is responsible for handling all user interface and browser communication logic. It's typically the layer that users interact with directly.
2. Application Layer (or Service Layer): This layer orchestrates application activity and controls the application's functionality by routing commands from the user interface to the infrastructure and domain layers.
3. Business Logic Layer (or Domain Layer): Contains business logic, rules, and domain knowledge. It's here where all the business processing happens and business rules are enforced.
4. Data Access Layer (or Persistence Layer): Responsible for managing the persistent state of the application and database interactions. It handles Create, Read, Update, Delete (CRUD) operations and often includes an Object-Relational Mapping (ORM) framework to manage the interaction with the database.
5. Infrastructure Layer: This layer can support all the other layers by providing services like logging, caching, networking, and security.

Purpose and Role

The main purpose of the layered architecture is to separate concerns and manage dependencies, making the system easier to manage, maintain, and develop. This structure allows developers to change or add a specific layer without impacting the others, thus promoting reusability and modularity.

Pros and Cons

Pros:

1. Modularity: Different layers can be developed simultaneously by separate teams.
2. Maintainability: Changes in one layer do not impact others, making it easier to update or add new features.
3. Reusability: Layers can potentially be reused across multiple projects.

Cons:

1. Performance: Each layer the data must pass through adds latency to the data transfer.
2. Complexity: Layered architecture might be overkill and unnecessarily complex in simple applications.
3. Rigidity: Over-reliance on the architecture can result in a lack of flexibility and innovation.

Example

A common example of layered architecture can be found in a web application where the user interface (presentation layer) interacts with an application layer to carry out operations, which then apply business logic (business logic layer) and interact with the database (data access layer). These operations may be facilitated by infrastructure services, like logging or security protocols.