Web service

Web service

A Web service (also Web Service) is defined by the W3C as "a software system designed to support interoperable machine-to-machine interaction over a network" [cite web |url=http://www.w3.org/TR/ws-gloss/ |title=Web Services Glossary] . Web services are frequently just Web APIs that can be accessed over a network, such as the Internet, and executed on a remote system hosting the requested services.

The W3C Web service definition encompasses many different systems, but in common usage the term refers to clients and servers that communicate over the HTTP protocol used on the Web. Such services tend to fall into one of two camps: Big Web Services and RESTful Web Services.

"Big Web Services" use XML messages that follow the SOAP standard and have been popular with traditional enterprise. In such systems, there is often 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 Spring, Apache Axis2 and Apache CXF being notable exceptions). Some industry organizations, such as the WS-I, mandate both SOAP and WSDL in their definition of a Web service.

More recently, "RESTful Web services" have been regaining popularity, particularly with Internet companies. These also meet the W3C definition, and are often better integrated with HTTP than SOAP-based services. They do not require XML messages or WSDL service-API definitions.



To improve interoperability of Web Services, the WS-I publishes profiles. A profile is a set of core specifications (SOAP, WSDL, ...) in a specific version (SOAP 1.1, UDDI 2, ...) with some additional requirements to restrict the use of the core specifications.The WS-I also publishes use cases and test tools to help deploying profile compliant Web Service.

Additional specifications, WS

Some specifications have been developed or are currently being developed to extend Web Services capabilities. These specifications are generally referred to as WS-*. Here is a non-exhaustive list of these WS-* specifications.;WS-Security: Defines how to use XML Encryption and XML Signature in SOAP to secure message exchanges, as an alternative or extension to using HTTPS to secure the channel.;WS-Reliability: An OASIS standard protocol for reliable messaging between two Web services.;WS-Transaction: A way of handling transactions.

Some of these additional specifications have come from the W3C. There is much discussion around the organization's participation, as the general Web and the Semantic Web story appear to be at odds with much of the Web Services vision. This has surfaced most recently in February 2007, at the Web of Services for the Enterprise workshop. Some of the participants advocated a withdrawal of the W3C from further WS-* related work, and a focus on the core Web.

In contrast, OASIS has standardized many Web service extensions, including Web Services Resource Framework and WSDM.

tyles of use

Web services are a set of tools that can be used in a number of ways. The three most common styles of use are RPC, SOA and REST.

Remote procedure calls

RPC Web services present a distributed function (or method) call interface that is familiar to many developers. Typically, the basic unit of RPC Web services is the WSDL operation.

The first Web services tools were focused on RPC, and as a result this style is widely deployed and supported. However, it is sometimes criticised for not being loosely coupled, because it was often implemented by mapping services directly to language-specific functions or method calls. Many vendors felt this approach to be a dead end, and pushed for RPC to be disallowed in the WS-I Basic Profile.

ervice-oriented architecture

Web services can also be used to implement an architecture according to Service-oriented architecture (SOA) concepts, where the basic unit of communication is a message, rather than an operation. This is often referred to as "message-oriented" services.

SOA Web services are supported by most major software vendors and industry analysts. Unlike RPC Web services, loose coupling is more likely, because the focus is on the "contract" that WSDL provides, rather than the underlying implementation details.

Representational state transfer

Finally, RESTful Web services attempt to emulate HTTP and similar protocols by constraining the interface to a set of well-known, standard operations (e.g., GET, PUT, DELETE). Here, the focus is on interacting with stateful resources, rather than messages or operations.RESTful Web services can use WSDL to describe SOAP messaging over HTTP, which defines the operations, or can be implemented as an abstraction purely on top of SOAP (e.g., WS-Transfer).

WSDL version 2.0 offers support for binding to all the HTTP request methods (not only GET and POST as in version 1.1) so it enables a better implementation of RESTful Web services [cite web |url=http://www.w3.org/TR/2007/REC-wsdl20-adjuncts-20070626/#_http_binding_default_rule_method |title=Web Services Description Language (WSDL) Version 2.0 Part 2: Adjuncts] .However, support for this specification is still poor in software development kits, which often offer tools only for WSDL 1.1.


Critics of non-RESTful Web services often complain that they are too complex [ [http://www.tbray.org/ongoing/When/200x/2004/09/21/WS-Research ongoing · WS-Pagecount ] ] and based upon large software vendors or integrators, rather than open source implementations.

One big concern of the REST Web Service developers is that the SOAP WS toolkits make it easy to define new interfaces for remote interaction, often relying on introspection to extract the WSDL and service API from Java, C# or VB code. This is viewed as a feature by the SOAP stack authors (and many users) but it is feared that it can increase the brittleness of the systems, since a minor change on the server (even an upgrade of the SOAP stack) can result in different WSDL and a different service interface. The client-side classes that can be generated from WSDL and XSD descriptions of the service are often similarly tied to a particular version of the SOAP endpoint and can break if the endpoint changes or the client-side SOAP stack is upgraded. Well designed SOAP endpoints (with handwritten XSD and WSDL) do not suffer from this but there is still the problem that a custom interface for every service 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 and HTTP in enveloping and transport. At the same time, there are also emerging XML parsing/indexing technologies, such as VTD-XML, that promise to address those XML-related performance issues.

imilar efforts

There are several other approaches to solving the set of problems that Web services address, both preceding and contemporary to it. RMI was one of many middleware systems that have seen wide deployment. More ambitious efforts like CORBA and DCOM attempted to effect distributed objects, which Web services implementations sometimes try to mimic.

More basic efforts include XML-RPC, a precursor to SOAP that was only capable of RPC, and various forms of HTTP usage without SOAP.

ee also

*List of Web service Frameworks
* List of web service protocols
* List of Web service specifications
*Service system
*Service Oriented Architecture
*Enterprise Information Integration (EII)
*Business Intelligence 2.0 (BI 2.0)
*Devices Profile for Web Services
*Web Processing Service
* Web server
*Microsoft Connected Services Framework
*Web Services Discovery
*Global SOA
*Service-Oriented Modeling Framework


External links

* [http://www.w3.org/2002/ws/ W3C Web Services Activity home page]
* [http://www.w3.org/TR/ws-arch/ Web Services Architecture] (W3C Working Group Note)
* [http://www.ibm.com/developerworks/webservices/library/ws-securtrans/ Secure, Reliable, Transacted Web Services] (IBM/Microsoft white paper)
* [http://www.ibm.com/developerworks/edu/ws-dw-ws-soa-autotest3.html?S_TACT=105AGY59&S_CMP=WIKITU&ca=dtl-1808tu1 Automate Web service testing, Part 3: Test a secured Web service with IBM Rational Software Architect and XMLUnit] (IBM developerWorks tutorial - advanced level)
* [http://webservices.sys-con.com/read/250512.htm The Performance Woe of Binary XML]
* [http://www2008.org/papers/fp389.html Where to find Web Services on the Web: Investigating Web Services on the World Wide Web (2008)]

Look at other dictionaries:

  • Web service — Service Web Un service web est un programme informatique permettant la communication et l échange de données entre applications et systèmes hétérogènes dans des environnements distribués. Il s agit donc d un ensemble de fonctionnalités exposées… …   Wikipédia en Français

  • Web-Service — Dieser Artikel oder Abschnitt bedarf einer Überarbeitung. Näheres ist auf der Diskussionsseite angegeben. Hilf mit, ihn zu verbessern, und entferne anschließend diese Markierung. Ein Webservice oder Webdienst ist eine Software Anwendung, die mit… …   Deutsch Wikipedia

  • Web Service — Dieser Artikel oder Abschnitt bedarf einer Überarbeitung. Näheres ist auf der Diskussionsseite angegeben. Hilf mit, ihn zu verbessern, und entferne anschließend diese Markierung. Ein Webservice oder Webdienst ist eine Software Anwendung, die mit… …   Deutsch Wikipedia

  • Web Service — saityno paslauga statusas T sritis dirbtinis intelektas apibrėžtis Standartizuota saityno taikomųjų programų paslauga, sukurta remiantis atviraisiais interneto standartais XML (duomenims žymėti), SOAP (duomenims siųsti), WSDL (paslaugoms… …   Lithuanian dictionary (lietuvių žodynas)

  • Web service — noun A software system designed to support interoperable machine to machine interaction over a network …   Wiktionary

  • Web Service Choreography — (WS Choreography) is a specification by the W3C defining a XML based business process modeling language that describes collaboration protocols of cooperating Web Service participants, in which services act as peers, and interactions may be long… …   Wikipedia

  • Web Service Resource Framework — (WSRF) forma parte de la família de especificaciones relativas a servicios web publicadas por OASIS. Los principales impulsores de esta especificación son IBM y la Globus Alliance. Un servicio web no tiene estado, es decir, no mantiene ninguna… …   Wikipedia Español

  • Web Service Description Language — Vorlage:Infobox Dateiformat/Wartung/magic fehltVorlage:Infobox Dateiformat/Wartung/genre fehltVorlage:Infobox Dateiformat/Wartung/website fehlt Web Services Description Language …   Deutsch Wikipedia

  • Web Service Modeling Ontology — Die Web Service Modeling Ontology (WSMO) stellt ein Meta Modell für die Web Service Modeling Language (WSML) dar. Sie bildet die konzeptuelle Grundlage dafür und definiert eine formale Sprache mit deren Hilfe es möglich ist, alle wichtigen… …   Deutsch Wikipedia

  • Web service level agreement — A web service level agreement (WSLA) is a standard for service level agreement compliance monitoring of web services. It allows authors to specify the performance metrics associated with a web service application, desired performance targets, and …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.