13. What is REST and what are its core principles?

REST (Representational State Transfer) is an architectural style for designing networked applications that uses standard HTTP operations for communication between client and server. REST is based on several core principles:

1. Uniform Interface: Unifying the interaction between client and server through standard HTTP methods (GET, POST, PUT, DELETE).

2. Statelessness: Each request from client to server must contain all the information needed to understand and process the request. The server does not store any client state between requests.

3. Cacheability: Server responses can be marked as cacheable or not, allowing clients to store responses in a cache to improve performance.

4. Layered System: The architecture can be composed of multiple layers, each performing different functions such as caching, business logic, or security.

5. Code on Demand (optional): The server can provide executable code to the client in response to a request (e.g., JavaScript), enhancing functionality without requiring updates to the application itself.

6. Resource Manipulation through Representations: Resources are identified by URIs and manipulated using representations such as JSON or XML that describe the current state of the resource.

Understanding and applying REST principles is crucial for designing scalable, efficient, and maintainable web services.