NetWeaver Gateway- Introduction to REST
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The document introduces Representational State Transfer (REST) and how it has been implemented through HTTP. It defines REST as a set of six architectural constraints for networked systems, including separating concerns in a client-server model and making interactions stateless and uniform. HTTP implements the core REST operations of create, read, update and delete through its request methods. The document aims to explain REST as a design philosophy rather than a protocol.
NetWeaver Gateway- Introduction to REST
- 1. GW100 SAP NetWeaver Gateway Introduction to REST May, 2012 INTE RNA L
- 2. Objectives At the end of this chapter, you will understand: Ÿ What Representational State Transfer (REST) is Ÿ How REST has been implemented as HTTP(S) © 2012 SAP AG. All rights reserved. 2
- 3. Agenda u REST – The Foundational Principles of the World Wide Web u HTTP – An Implementation of the Principles of REST © 2012 SAP AG. All rights reserved. 3
- 4. Agenda u REST – The Foundational Principles of the World Wide Web u HTTP – An Implementation of the Principles of REST © 2012 SAP AG. All rights reserved. 4
- 5. Correcting A Common Misunderstanding So, Representational State Transfer (REST) is some kind of network protocol like HTTP or SOAP? NO! REST is a design philosophy that defines six architectural constraints. These constraints govern the large-scale behaviour of the participants within in a networked software system. Any software system that conforms to the constraints of REST, is said to be RESTful. The World Wide Web is the most prominent example of a software system that fully implements the principles of REST. © 2012 SAP AG. All rights reserved. 5
- 6. REST: A Software Design Philosophy – 1/6 REST defines 6 architectural constraints: Communication between participants must: 1) Implement the Client-Server model The client-server model allows for the client and server software components to be developed independently. It further assumes that the client will take no part in long-term data storage and that the server will take no part in the presentation of the data it supplies. This principle is known as the “Separation of Concerns”. © 2012 SAP AG. All rights reserved. 6
- 7. REST: A Software Design Philosophy – 2/6 REST defines 6 architectural constraints: Communication between participants must: 2) Be layered When the client communicates with a server, it should not ordinarily be able to distinguish whether it has communicated with the actual end-point server that will supply the requested information, or some intermediate server used for system scalability or security. © 2012 SAP AG. All rights reserved. 7
- 8. REST: A Software Design Philosophy – 3/6 REST defines 6 architectural constraints: Communication between participants must: 3) Be stateless A stateless interface requires the client to supply all the necessary information for the server to process the request. Session information must be held on the client. There is no prohibition against the server holding client state information, only that the state information must be known to, and addressable by the client. © 2012 SAP AG. All rights reserved. 8
- 9. REST: A Software Design Philosophy – 4/6 REST defines 6 architectural constraints: Communication between participants must: 4) Be Uniform (meaning that) a. The server must provide the client with a representation of its resources b. A means must be provided for the client to manipulate those resources (E.G. Provide operations such as Create, Read, Update, Delete etc) c. All responses sent to the client must be self-describing d. The manipulation of server-side resources may only be performed by hypermedia supplied by the server.* This constraint is generally regarded as the core concept of REST. A server exposes a self-describing resource that can be manipulated by a client via a hypermedia link. * Known as “Hypermedia as the Engine of Application State” or HATEOAS. Remember this principle because it is key to the success of OData! © 2012 SAP AG. All rights reserved. 9
- 10. REST: A Software Design Philosophy – 5/6 REST defines 6 architectural constraints: 5) Server responses must define whether or not they are Cacheable Response caching In order to improve performance and scalability, any information supplied by the server must carry with it an indicator to denote whether or not it can be cached for future use. Any system within the layered architecture could act as a cache. © 2012 SAP AG. All rights reserved. 10
- 11. REST: A Software Design Philosophy – 6/6 REST defines 6 architectural constraints: 6) The Server should be able to deliver Code-On-Demand to the client At the request of the client, the server should be able to supply additional executable code to extend the client’s capabilities. This principle is used every time a browser requests a JavaScript file from a webserver. © 2012 SAP AG. All rights reserved. 11
- 12. Agenda u REST – The Foundational Principles of the World Wide Web u HTTP – An Implementation of the Principles of REST © 2012 SAP AG. All rights reserved. 12
- 13. HTTP(S) – An Implementation of the REST Constraints HTTP(S) is the Protocol that Drives the World Wide Web A server-side resource can be manipulated in 4 basic ways. These four basic REST operations have given rise the the acronym CRUD. REST Operation HTTP Method Create a resource POST Retrieve one or more resources GET Update a resource PUT Delete a resource DELETE HTTP(S) implements server-side resource manipulation by providing a set of “Methods” that correspond to REST operations. © 2012 SAP AG. All rights reserved. 13
- 14. Summary u REST is a set of 6 design constraints, not a network protocol. u The REST design constraints are fully implemented by the HTTP protocol. u The World Wide Web is an example of a fully RESTful software system. u Just because an application protocol makes use of HTTP, does not guarantee it to be RESTful! © 2012 SAP AG. All rights reserved. 14
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