11/5/12 Web serv ice - Wikipedia, the f ree ency clopedia

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Web services architecture.

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A Web service is a method of communication between twoelectronic devices over the World Wide Web.

The W3C defines a "Web service" as "a software system designed tosupport interoperable machine-to-machine interaction over anetwork". It has an interface described in a machine-processableformat (specifically Web Services Description Language, known bythe acronym WSDL). Other systems interact with the Web service ina manner prescribed by its description using SOAP messages,typically conveyed using HTTP with an XML serialization in

conjunction with other Web-related standards."[1]

The W3C also states, "We can identify two major classes of Webservices, REST-compliant Web services, in which the primarypurpose of the service is to manipulate XML representations of Webresources using a uniform set of "stateless" operations; and arbitrary Web services, in which the service may expose

an arbitrary set of operations."[2]

Contents

1 Web API

1.1 Representational state transfer (REST)

2 Big Web services3 Automated design methodologies

4 Web services which use markup languages

5 Criticisms

6 References

7 External links

Web API

Web API is a development in Web services (in a movement called Web 2.0) where emphasis has been moving

away from SOAP based services towards representational state transfer (REST) based communications.[3] RESTservices do not require XML, SOAP, or WSDL service-API definitions.

Web APIs allow the combination of multiple Web services into new applications known as mashups.[4]

Representational state transfer (REST)

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en.wikipedia.org/wiki/Web_serv ices

Web services in a service-oriented architecture.

Main article: Representational state transfer

REST attempts to describe architectures that use HTTP or similar protocols by constraining the interface to a setof well-known, standard operations (like GET, POST, PUT, DELETE for HTTP). Here, the focus is on interactingwith stateless resources, rather than messages or operations. Clean URLs are tightly associated with the RESTconcept.

An architecture based on REST can use WSDL to describe SOAP messaging over HTTP, can be implemented asan abstraction purely on top of SOAP (e.g.,WS-Transfer), or can be created without usingSOAP at all.

WSDL version 2.0 offers support for bindingto all the HTTP request methods (not onlyGET and POST as in version 1.1) so it enablesa better implementation of RESTful web

services.[5] However, support for thisspecification is still poor in softwaredevelopment kits, which often offer tools onlyfor WSDL 1.1.

Big Web services

"Big Web services" use Extensible Markup Language (XML) messages that follow the SOAP standard and havebeen popular with the traditional enterprises. In such systems, there is often a machine-readable description of theoperations offered by the service written in the Web Services Description Language (WSDL). The latter is not arequirement of a SOAP endpoint, but it is a prerequisite for automated client-side code generation in many Javaand .NET SOAP frameworks (frameworks such as Apache Axis2, Apache CXF, and Spring being notableexceptions). Some industry organizations, such as the WS-I, mandate both SOAP and WSDL in their definition ofa Web service.

Automated design methodologies

Automated tools can aid in the creation of a Web service. For services using WSDL it is possible to eitherautomatically generate WSDL for existing classes (a bottom-up strategy) or to generate a class skeleton givenexisting WSDL (a top-down strategy).

A developer using a bottom up method writes implementing classes first (in some programming language),

and then uses a WSDL generating tool to expose methods from these classes as a Web service.[6] This is

often the simpler approach.A developer using a top down method writes the WSDL document first and then uses a code generating tool

to produce the class skeleton, to be completed as necessary. This way is generally considered more difficult

but can produce cleaner designs [7]

Web services which use markup languages

11/5/12 Web serv ice - Wikipedia, the f ree ency clopedia

3/4

There are a number of web services which use markup languages:

Web template

Web Services Description Language (WSDL) from the W3CXML Interface for Network Services (XINS) provides a POX-style Web service specification format

Web Services Conversation Language (WSCL)Web Services Flow Language (WSFL) (superseded by BPEL)

WS-MetadataExchangeRepresentational state transfer (REST) versus remote procedure call (RPC)

XML-RPC - XML Remote Procedure Call

Criticisms

Critics of non-REST Web services often complain that they are too complex[8] and based upon large softwarevendors or integrators, rather than typical open source implementations. There are open source implementationslike Apache Axis and Apache CXF.

One key concern of the REST Web service developers is that the SOAP WS toolkits make it easy to define newinterfaces for remote interaction, often relying on introspection to extract the WSDL, since a minor change on the

server (even an upgrade of the SOAP stack) can result in different WSDL and a different service interface.[9] Theclient-side classes that can be generated from WSDL and XSD descriptions of the service are often similarly tied toa particular version of the SOAP endpoint and can break, if the endpoint changes or the client-side SOAP stack isupgraded. Well-designed SOAP endpoints (with handwritten XSD and WSDL) do not suffer from this, but acustom interface for every service still requires a custom client for every service.

There are also concerns about performance due to Web services' use of XML as a message format and

SOAP/HTTP in enveloping and transporting.[10]

References

1. ^ "Web Services Glossary" (http://www.w3.org/TR/2004/NOTE-ws-gloss-20040211/) . W3C. February 11, 2004.http://www.w3.org/TR/2004/NOTE-ws-gloss-20040211/. Retrieved 2011-04-22.

2. ^ "Relationship to the World Wide Web and REST Architectures" (http://www.w3.org/TR/ws-arch/#relwwwrest). Web Services Architecture. W3C. http://www.w3.org/TR/ws-arch/#relwwwrest. Retrieved 2011-04-22.

3. ^ Benslimane, Djamal; Schahram Dustdar, and Amit Sheth (2008). "Services Mashups: The New Generation ofWeb Applications"(http://dsonline.computer.org/portal/site/dsonline/menuitem.9ed3d9924aeb0dcd82ccc6716bbe36ec/index.jsp?&pName=dso_level1&path=dsonline/2008/09&file=w5gei.xml&xsl=article.xsl) . IEEE Internet Computing, vol.12, no. 5. Institute of Electrical and Electronics Engineers. pp. 13–15.http://dsonline.computer.org/portal/site/dsonline/menuitem.9ed3d9924aeb0dcd82ccc6716bbe36ec/index.jsp?&pName=dso_level1&path=dsonline/2008/09&file=w5gei.xml&xsl=article.xsl.

4. ^ "Mashup Dashboard" (http://www.programmableweb.com/mashups) . ProgrammableWeb.com. 2009.http://www.programmableweb.com/mashups.

5. ^ "Web Services Description Language (WSDL) Version 2.0 Part 2: Adjuncts" (http://www.w3.org/TR/2007/REC-wsdl20-adjuncts-20070626/#_http_binding_default_rule_method) . W3C. http://www.w3.org/TR/2007/REC-wsdl20-adjuncts-20070626/#_http_binding_default_rule_method.

6. ^ "Help - Creating bottom-up Web services" (http://help.eclipse.org/help33/index.jsp?

topic=/org.eclipse.jst.ws.doc.user/concepts/cwsbtmup.html) . Eclipse. http://help.eclipse.org/help33/index.jsp?

11/5/12 Web serv ice - Wikipedia, the f ree ency clopedia

en.wikipedia.org/wiki/Web_serv ices

topic=/org.eclipse.jst.ws.doc.user/concepts/cwsbtmup.html) . Eclipse. http://help.eclipse.org/help33/index.jsp?topic=/org.eclipse.jst.ws.doc.user/concepts/cwsbtmup.html. Retrieved 2011-04-22.

7. ^ "Help - Creating top-down Web services" (http://help.eclipse.org/help33/index.jsp?topic=/org.eclipse.jst.ws.doc.user/concepts/cwstopdown.html) . Eclipse. http://help.eclipse.org/help33/index.jsp?topic=/org.eclipse.jst.ws.doc.user/concepts/cwstopdown.html. Retrieved 2011-04-22.

8. ^ Bray, Tim (October 28, 2004). "WS-Pagecount" (http://www.tbray.org/ongoing/When/200x/2004/09/21/WS-Research) . TBray.org. http://www.tbray.org/ongoing/When/200x/2004/09/21/WS-Research. Retrieved 2011-04-22.

9. ^ "Rethinking the Java SOAP Stack" (http://www.hpl.hp.com/techreports/2005/HPL-2005-83.html) . HP.http://www.hpl.hp.com/techreports/2005/HPL-2005-83.html. Retrieved 2011-04-22.

10. ^ Gray, N. A. B. (2005). "Performance of Java Middleware - Java RMI, JAXRPC, and CORBA"(http://ro.uow.edu.au/infopapers/676/) . University of Wollongong. pp. 31–39.http://ro.uow.edu.au/infopapers/676/. Retrieved January 11, 2011. "The results presented in this paper show thatthe nature of response data has a greater impact on relative performance than has been allowed for in mostprevious studies."

External links

Messaging Design Pattern and a distributed component/service model

(http://jt.dev.java.net/files/documents/5553/149793/MDPdistributedModel.pdf)

W3C Web Services Activity home page (http://www.w3.org/2002/ws/)Web Services Architecture (http://www.w3.org/TR/ws-arch/) (W3C Working Group Note)

Where to find Web Services on the Web: Investigating Web Services on the World Wide Web (2008)

(http://www2008.org/papers/fp389.html)NIST SP800-95 Guide to Secure Web Services (http://csrc.nist.gov/publications/nistpubs/800-95/SP800-

95.pdf)

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