REST (Representational State Transfer) is an architectural style for web APIs characterized by principles such as a uniform interface, client-server separation, statelessness, cacheability, layered systems, and optional code on demand. Key concepts include resource identification, manipulation through representations, and self-descriptive messages to facilitate client-server interactions. RESTful APIs use hypermedia links and can be easily extended across various platforms.

1. REST API

2. REST
• Acronym for REpresentational State Transfer.
• It is NOT A PROTOCOL
• It is an architectural style
• A Web API conforming to the REST architectural style is called a REST
API (or RESTful API).

3. Guiding Principles
• These provides simplicity, scalability and statelessness.
• The six guiding principles or constraints are:

4. Principles
1. Uniform Interface
Identification of resources – unique identity
Manipulation of resources through representations – uniform server
response representations, used to modify resource state in server
Self – descriptive messages – info. on message processing, additional
information’s
2. Client – Server
Separation of concerns of client & server.
Improves portability across platform
Improves scalability by simplifying server components
Make sure the client server interface doesn’t break

5. Principles
3. Stateless
Each client request must contain all necessary & complete request.
Client application must keep the session state.
4. Cacheable
Responses should be labelled cacheable or non – cacheable.
If cacheable, response data can be reused for a specified period.
5. Layered System
Hierarchical layers, each component can’t be seen beyond the layer they are
interacting.
6. Code on Demand (Optional) – reduces re - implementation

6. Resource
• Key abstraction of information
• Any information is a resource.
• Resource Representation – state of the resource.
• Resource Representations consist of
• Data
• Metadata
• Hypermedia links – helps client to transition to the next desired state.

7. Resource
• Resource Identifiers
• Used to identify each resource involved in the interactions between the client
and server components
• Hypermedia
• Media type – data format of the representation
• RESTful API looks like a hypertext.
• Self – Descriptive
• Resource representations shall be self – descriptive.
• Client doesn’t need to know if resource is a device or an employee.