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Advanced Web Technologies

Advanced Web Technologies. Lecture #4 By : Faraz Ahmed. Contents. Personnel Requirements SQA Tasks Improving SQA. WebServices. “A software system designed to support interoperable machine-to-machine interaction over a network.” [1]. WebServices (simple def).

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Advanced Web Technologies

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  1. Advanced Web Technologies Lecture #4 By: Faraz Ahmed

  2. Contents • Personnel Requirements • SQA Tasks • Improving SQA

  3. WebServices “A software system designed to support interoperable machine-to-machine interaction over a network.” [1]

  4. WebServices (simple def) A web service is just a web page meant for a computer to request and process

  5. Benefits? • Interoperability. • Reusability. • Connecting Existing Software. • Maintainability.

  6. WSDL • Based on XML • Language for describing the service to clients. • Description {interactions, Inputs/Outputs, Location, Protocols, Data Formats} • Contract between Client and server developers. • Alternatives: Web Access Description Language

  7. WSDL in its simplest form1 1 http://w3Schools.com

  8. WSDL in its simplest form

  9. <portType> • One-way : The operation can receive a message but will not return a response • Request-response : The operation can receive a request and will return a response • Solicit-response : The operation can send a request and will wait for a response • Notification : The operation can send a message but will not wait for a response

  10. Styles[2] How to translate a WSDL into SOAP messages. Document RPC

  11. UDDI • Universal Description, Discovery and Integration (UDDI) for web Services registration. • Platform independent. • However lack of public UDDIs has harmed the initiative[3]. • UDDI Browser [4]

  12. SOAP • Simple Object access Protocol • CORBA used to be difficult to use. • Alternatives: XML-RPC, JSON-RPC • The recommendations do not require the use of SOAP for webservices.

  13. SOAP • Complex datatypes are easily shared as compared to the simplicity of others which hinder such sharing[5]. • SOAP services are loosely coupled as compared to their predecessors.

  14. Sample Web Services • Google's Web Service - access the Google search engine • Amazon's Web Service - access Amazon's product information • XMethods • http://www.webservicex.net/ws/wscatlist.aspx

  15. The interaction

  16. REST[6] • Representational State Transfer • Each URL represents a different state and that state is transferred. OPAQUE • Resources are key elements and identified by URIs • Anything of interest is a resource. • Gives rise to resource oriented architecture.

  17. REST features • Client Server • Stateless • Cacheable • Layered System • Uniform interface

  18. But why Stateless?? • Visibility : A server doesn’t have to look further • Reliability : Easy recovery from failures • Scalability : Limited utilization of server resources.

  19. Uniform interface •  identification of resources; • manipulation of resources through representations; • self-descriptive messages; and, • hypermedia as the engine of application state

  20. The Power of URI • Maintaining a trail of what and how we got to the point

  21. GET: fetch information • To fetch a web page, the browser does a GET on some URI and retrieves a representation (HTML, plain text, JPEG, or whatever) of the resource identified by that URI • GET is fundamental to browsers because mostly they just browse • REST requires a few more verbs to allow taking actions

  22. Verbs • GET • POST • PUT • DELETE

  23. REST vs. SOAP • REST • Lightweight - not a lot of extra xml markup • Human Readable Results • Easy to build - no toolkits required • Lower Learning Curve • Uses the same paradigm as HTTP • SOAP • Easy to consume - sometimes • Rigid - type checking, adheres to a contract • Development tools

  24. Recommended Reading! • How I explained REST to my wife!!! [7]

  25. Bibliography 1) “REST”, http://oreilly.com/catalog/pwebserperl/chapter/ch11.pdf, visited on 24th Jan 2011.

  26. References • “Web Services Glossary”, http://www.w3.org/TR/ws-gloss/, visited 23rd Jan 2011. • “Which Style of WSDL should I use”, http://www.ibm.com/developerworks/webservices/library/ws-whichwsdl/, visited 23rd Jan 2011. • “IBM and Microsoft discontinue Public UDDI Registry”, http://www.webservicessummit.com/News/UDDI2006.htm, visited on 23rd Jan 2011. • “SOAP Client”, http://www.soapclient.com/uddisearch.html, visited on 23rd Jan 2011. • “XML-RPC vs. SOAP”, http://weblog.masukomi.org/writings/xml-rpc_vs_soap.htm, visited on 23rd Jan 2011. • “Representational State Transfer”, http://www.ics.uci.edu/~fielding/pubs/dissertation/rest_arch_style.htm#sec_5_1, visited on 24th Jan 2011. • “How I explained REST to my wife”, http://tomayko.com/writings/rest-to-my-wife, visited on 24th Jan 2011.

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