The Richardson’s Maturity Model (RMM) was developed by Leonard Richardson. It classifies REST-based Web services and REST principles they should depend on.
Level 0 – Services under this category use http as a transport mechanism against single URI. Typically, HTTP POST is used to make service calls. For e.g. SOAP or old XML-RPC
Level 1 – Resources – This level introduces multiple URIs, which means breaking monolithic service with various operations into a service with multiple services with different resources.
Level 2- Http Verb – This level uses HTTP Verbs to perform corresponding CRUD operations. For e.g. GET to read, POST to create, PUT to update, DELETE to delete
Level 3- Hypermedia Links– In this level services use a hyperlink to maintain state. For e.g. HATEOS
