Introduction to REST Web REST Web Services Characteristics Services - PDF document

Introduction to REST Web Services 2/14/2009 Agenda  What is REST? Introduction to REST Web  REST Web Services Characteristics Services  Principle of REST Web Services Design  Semantic of HTTP/1.1 Operations Asst. Prof. Dr. Kanda Runapongsa Saikaew  Assets and Drawbacks (krunapon@kku.ac.th) Department of Computer Engineering  Security Khon Kaen University  REST vs. SOAP 1 2 What is REST? Why Representational State Transfer? (1/2)  REST is a term proposed by Roy  The Web is comprised of resources Fielding in his Ph.D. dissertation  A resource is any item of interest  REST is to describe an archit itecture ecture http://gear.kku.ac.th/~krunapon styl yle of networked systems  A representation of the resource is  REST is an acronym standing for returned Representational State Transfer  The representation places the client application in a state 3 4 Roy Fielding‟s Explanation Why Representational State Transfer? (2/2)  The result of the client traversing a  Representational State Transfer is intended to evoke an image of how a well- hyperlink results in another resource designed Web application behaves: a is accessed network of web pages (a virtual state  The new representation places the machine), where the user progresses client application into yet another through an application by selecting links state (state transitions), resulting in the next page (representing the next state of the  The client application changes application) being transferred to the user (transfers) state with each resource and rendered for their use.” representation  Representational State Transfer! 5 6 Dr. Kanda Runapongsa Saikaew, Computer Engineering, Khon Kaen University 1

Introduction to REST Web Services 2/14/2009 REST Uses These Standards REST, An Architectural Style, Not a Standard  REST is not a standard  HTTP  You will not see the W3C putting out a  URL REST specification  XML/HTML/GIF/JPEG/etc  REST is just an architectural style (Resource Representations)  You can only understand the style  text/xml, text/html, image/gif, and design your Web services in that image/jpeg, etc (Resource Types, style MIME Types)  Analogous to the client-server architectural style, there is no client- server standard 7 8 The Classic REST System Parts Depot Web Services  The Web is a REST system  Parts Depot has deployed some web services to enable its  Many of those Web services that you have been using these many years customers to  Book-ordering services  Get a list of parts  Search services  Get detailed information about a  Online dictionary services particular part  REST is concerned with the “big  Submit a purchase order picture” of the Web  It does not deal with implementation details 9 10 Get Parts List The Client will Receive  The web service makes available a <?xml version=“ 1.0 ”?> <p:Parts xmlns:p=„http://www.parts - depot.com‟ URL to a parts list resource xmlns:xlink=„http://www.w 3.org/1999 /xlink‟>  For example, a client would use this <Part id=„ 00345 ‟ xlink:href=„http://www.parts - depot.com/parts/00345 ‟/> URL to get the parts list <Part id=„ 00346 ‟ xlink:href=„http://www.parts -  http://www.parts-depot.com/parts depot.com/parts/00346 ‟/> </p:Parts>  Parts Depot is free to modify the  The parts has links to get detailed info about each part underlying implementation of this  The client transfers from one state to the next by resource without impacting clients examining and choosing from among the alternative URLs in the response document. (loose coupling) 11 12 Dr. Kanda Runapongsa Saikaew, Computer Engineering, Khon Kaen University 2

Introduction to REST Web Services 2/14/2009 Get Detailed Part Data The Client will Receive <?xml version=“ 1.0 ”?>  The web service makes available a <p:Part xmlns:p= „http://www.parts -depot.com ‟ URL to each part resource xmlns:xlink=„http://www.w 3.org/1999 /xlink‟>  For example, here‟s how a client <Part-ID>00345</Part-ID> requests part 00345: <Name>Widget-A</Name>  http://www.parts-depot.com/parts/00345 <Description>This part is used within the frap assembly</Description> … <Quantity>10</Quantity> </p:Part> 13 14 Agenda REST Web Services Characteristics (1/3)  What is REST?  Client-server  A pull-based interaction style:  REST Web Services Characteristics consuming components pull  Principle of REST Web Services representations Design  Stateless  SOAP vs. REST Style  Each request from client to server must  REST Assets and Drawbacks contain all the information necessary to understand the request  Security with REST  Cannot take advantage of any stored  Public Web Services text on the server 15 16 REST Web Services Characteristics (2/3) REST Web Services Characteristics (3/3)  Cache  Interconnected resource  To improve network efficiency, responses representations must be capable of being labeled as  The representations of the resources cacheable or non-cacheable are interconnected using URLs, thereby  Uniform interface enabling a client to progress from one  All resources are accessed with a generic state to another interface (e.g., HTTP GET, POST, PUT,  Layered components DELETE)  Named resources  Intermediaries, such as proxy servers, cache servers, gateways, etc, can be  The system is comprised of resources which inserted between clients and resources are named using a URL to support performance, security, etc. 17 18 Dr. Kanda Runapongsa Saikaew, Computer Engineering, Khon Kaen University 3

Introduction to REST Web Services 2/14/2009 Agenda Principles of REST Web Service Design (1/4)  What is REST?  The key to creating Web services in a REST network (i.e., the Web)  REST Web Services Characteristics is to identify all of the conceptual  Principle of REST Web Services entities that you wish to expose Design as services  Semantic of HTTP/1.1 Operations  Assets and Drawbacks  Above we saw some examples of resources: parts list, detailed part  Security data, purchase order  REST vs. SOAP 19 20 Principles of REST Web Service Design (2/4) Principles of REST Web Service Design (3/4)  Create a URL to each resource. The  Categorize your resources according to resources should be nouns, not verbs whether clients can just receive a representation of the resource or whether  For example, do not use this clients can modify (add to) the resource  http://www.parts-  All resources accessible via HTTP GET depot.com/parts/getPart?id=00345 should be side-effect free  Note the verb, getPart Instead, use a  No man/woman is an island noun  Put hyperlinks within resource  http://www.parts-depot.com/parts/00345 representation to enable clients to drill down for more information 21 22 Agenda Principles of REST Web Service Design (4/4)  Design to reveal data gradually  What is REST?  Don‟t reveal everything in a single response  REST Web Services Characteristics document  Principle of REST Web Services  Provide hyperlinks to obtain more details Design  Specify the format of response data using a schema (DTD, W3C Schema)  Semantic of HTTP/1.1 Operations  Describe how your services are to be  Assets and Drawbacks invoked using either a WSDL document or  Security simply an HTML document  REST vs. SOAP 23 24 Dr. Kanda Runapongsa Saikaew, Computer Engineering, Khon Kaen University 4

Introduction to REST Web Services 2/14/2009 Semantic of HTTP/1.1 Operations (1/3) Semantic of HTTP/1.1 Operations (2/3)  GET  POST  “Retrieve whatever information (in the  “Request that the origin server accept form of an entity) is identified by the the entity enclosed in the request as a Request- URI” new subordinate of the resource identified by the Request- URI”  Retrieve representation, shouldn‟t result in data modification  Annotation of existing resources, extending a database through an append operation  Posting a message to a bulletin board, or group of articles  Providing a block of data (e.g., form data) to a data-handling process 25 26 Agenda Semantic of HTTP/1.1 Operations (3/3)  PUT  What is REST?  “Requests that the enclosed entity be  REST Web Services Characteristics stored under the supplied Request- URI”,  Principle of REST Web Services create/put a new resource Design  DELETE  Semantic of HTTP/1.1 Operations  “Requests that the origin server deletes  Assets and Drawbacks the resource identified by the Request- URI”  Security  REST vs. SOAP 27 28 REST Assets REST Drawbacks  Development and testing without complex  Restrictions for GET length toolkits sometimes may be a problem  Debugging of REST requests with a web  No direct bridge to the OOP world browser  Difference between REST and RPC  Requires a HTTP client, available in every common language style may be subtle sometimes, but not  REST services can be easily used by AJAX necessarily in general case applications  APIs in REST style are more consumable than complex APIs  Lower learning curve for consumer  Everything accessible through universal API 29 30 Dr. Kanda Runapongsa Saikaew, Computer Engineering, Khon Kaen University 5