Web services architecture.
A web service is a method of communication between two electronic devices over the World Wide Web. A web service is a software function provided at a network address over the web or the cloud, it is a service that is "always on" as in the concept of utility computing.
The W3C defines a "Web service" as:
[...] a software system designed to support
interoperable machine-to-machine interaction over a
network. It has an interface described in a machine-processable format (specifically
WSDL). Other systems interact with the Web service in a 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 Web services,
REST-compliant Web services, in which the primary purpose of the service is to manipulate XML representations of
Web resources using a uniform set of "stateless" operations; and arbitrary Web services, in which the service may expose an arbitrary set of operations.
[2]
Web API
A web API is a development in web services where emphasis has been moving to simpler representational state transfer (REST) based communications.[3] RESTful APIs do not require XML-based web service protocols (SOAP and WSDL) to support their light-weight interfaces.
Web APIs allow the combination of multiple web resources into new applications known as mashups.[4]
WSDL version 2.0 offers support for binding to all the HTTP request methods (beyond GET and POST as in version 1.1) allowing for a "RESTful web services" approach.[5]
XML web services
XML web services use Extensible Markup Language (XML) messages that follow the SOAP standard and have been popular with the traditional enterprises. In such systems, there is often a machine-readable description of the operations offered by the service written in the Web Services Description Language (WSDL). The latter is not a requirement of a SOAP endpoint, but it is a prerequisite for automated client-side code generation in many Java and .NET SOAP frameworks (frameworks such as Apache Axis2, Apache CXF, Spring, gSOAP being notable exceptions). Some industry organizations, such as the WS-I, mandate both SOAP and WSDL in their definition of a web service.
Automated design methods
Automated tools can aid in the creation of a web service. For services using WSDL it is possible to either automatically generate WSDL for existing classes (a bottom-up strategy) or to generate a class skeleton given existing 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. This is simpler to develop but may be harder to maintain if the original classes are subject to frequent change.[6]
- 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 and is generally more resistant to change. As long as the message formats between sender and receiver do not change, changes in the sender and receiver themselves do not affect the web service. The technique is also referred to as "contract first" since the WSDL (or contract between sender and receiver) is the starting point.[7]
Web services that use markup languages
There are a number of web services that use markup languages:
Criticisms
Critics of non-RESTful web services often complain that they are too complex[8] and based upon large software vendors or integrators, rather than typical open source implementations.
There are also concerns about performance due to web services' use of XML as a message format and SOAP/HTTP in enveloping and transporting.[9]
See also
References
- ^ "Web Services Glossary". W3C. February 11, 2004. http://www.w3.org/TR/2004/NOTE-ws-glo ss-20040211/. Retrieved 2011-04-22.
- ^ "Relationship to the World Wide Web and REST Architectures". Web Services Architecture. W3C. http://www.w3.org/TR/ws-arch/#relwwwr est. Retrieved 2011-04-22.
- ^ Benslimane, D.; Dustdar, S.; Sheth, A. (2008). "Services Mashups: The New Generation of Web Applications". IEEE Internet Computing 10 (5): 13–15. doi:10.1109/MIC.2008.110. edit
- ^ "Mashup Dashboard". ProgrammableWeb.com. 2009. http://www.programmableweb.com/mashup s.
- ^ "Web Services Description Language (WSDL) Version 2.0 Part 2: Adjuncts". W3C. http://www.w3.org/TR/2007/REC-wsdl20- adjuncts-20070626/#_http_binding_defa ult_rule_method.
- ^ "Help - Creating bottom-up Web services". Eclipse. http://help.eclipse.org/help33/index. jsp?topic=/org.eclipse.jst.ws.doc.use r/concepts/cwsbtmup.html. Retrieved 2011-04-22.
- ^ "Help - Creating top-down Web services". Eclipse. http://help.eclipse.org/help33/index. jsp?topic=/org.eclipse.jst.ws.doc.use r/concepts/cwstopdown.html. Retrieved 2011-04-22.
- ^ Bray, Tim (October 28, 2004). "WS-Pagecount". TBray.org. http://www.tbray.org/ongoing/When/200 x/2004/09/21/WS-Research. Retrieved 2011-04-22.
- ^ Gray, N. A. B. (2005). "Performance of Java Middleware - Java RMI, JAXRPC, and CORBA". University of Wollongong. pp. 31–39. http://ro.uow.edu.au/infopapers/676/. Retrieved January 11, 2011. "The results presented in this paper show that the nature of response data has a greater impact on relative performance than has been allowed for in most previous studies."
External links
