A Web service is an application of software, which is clearly identifiable with uniform resource Identifier (URI) and whose interfaces can be defined, described and found as XML artifacts. A Web service supports the direct interaction with other software agents using XML based messages by the exchange over Internet-based minutes.

A Web service is not:

• Middleware - the switching component and the guarantee of transaction security are missing
• Enterprise Application integration - however Web services can find with Enterprise Application integration use

Architecture

Client programs send generally inquiries to to Web a service and these answer with the desired information. It is therefore occasionally maintained that Web services for computers are that, which web pages for humans are. Even if only one part of the possibilities of the Web describes services, this comparison is quite appropriate. Web services are meant not for human users, but for software systems, who automate data exchange and/or on distant computers call functions.

Web services orient themselves at service-oriented architecture (SOA) and unite therefore distributed and object-oriented programming standards and are directed toward economical solutions in the Internet.

The instances consumer, offerer and listing can be identified.

The offerer publishes the description of his services in a listing. The consumer scans the listing and selects the desired service. After possibly further minutes details are exchanged, the dynamic binding of the consumer takes place to the offerer. The consumer falls back now to methods.

Here three standards, which are based in each case on XML and are more near described in the associated articles, form the basis:

• UDDI as listing service for the registration of Web services. It makes the dynamic finding of the Web for services possible (e.g. the service of football results) by the consumer.
• WSDL for the description of the supported methods (e.g. Goal scorer king) and their parameters (e.g. Date) for the programmer.
• SOAP (or XML-RPC) to communication. Here the actual call is started.

Web services illustrate the three most important parts of co-operation between Client and servers: The Zusammenfinden, binding and data exchange.

Web services are attainable over a clear URI. The used platform-independent standards are able to decode and an application pass on distant method calls of arbitrary platforms. In this way a distributed architecture develops. Communication with Web services is made by messages, which can be transported over several minutes.

Examples

Thus there are Web for example since 2002 of the operator of the search machine Google a service, which offers the same possibilities of the Website as the user interface. So can look now programs with few calls for information in the Internet and use these for their own tasks. The Parsen of the Google web page is also only approximate none in addition equivalent alternative.

A further example is the interaction between airlines and travel agencies. The travel agencies offer flights of different airlines, of which the travel agencies at run-time over UDDI on their Web operational readiness level experienced and whose flights transfer them to their offer. The airlines make possibilities for looking up and/or a booking available of flights over the Web service. The customer can compare prices and dates of different flights directly on the Web operational readiness level of the travel agency now central and book.

Evaluation

Advantages

• The used open standards avoid any license costs. Since to this standards also the pervasive Internet-based technologies belong, they can be used also in many places. A cost advantage lies also here.

• By usually used HTTP minutes to the data communication only rarely problems with Firewalls, contrary to comparable technologies arise such as CORBA, DCOM or also Java of RMI. Web services are bound however not at HTTP and can also with other minutes such as smtp or ftp be transferred and are thus open for different application scenarios.

• From the use from and wide-spread Internet standards already existing (HTTP, XML etc.) results an open and flexible architecture, which is independent of the used platforms, programming languages and minutes. So for example Windows C# Clients behind a Firewall with Java servers, which are implemented on Linux, can communicate. Wide-spread standard minutes make an interoperability possible over any in the Internet away.

• The barriers to the entrance are comparatively low.

Disadvantages

• Safety aspects might concern the main difficulty the conversion from Web services. So it is to be noted in the case of transport that important Web services are coded or a Authentifizierung take place can. Whether HTTPS is sufficient here or solutions are to be preferred such as XML Signature, XML Encryption or SAML, should be weighed out.

• A special attention is on the performance. This is affected negatively by XML, Parsen and file size. The administration expense increases with strongly distributed systems. The Overhead is partly substantial.

• It is necessary more know-how than e.g. with Remote Procedure Call (RPC). Programming languages, with which one wants to merge Web services, need special libraries (e.g. CATHEDRAL). Interfaces must be defined exactly - that is much work.

Areas of application

Web services represent new beginnings in the context of Enterprise Application integration (EAI) and Grid Computing. The planned main operational area lies in the Business ton Businessrange (B2B). Business processes are to be completed problem-free over enterprise borders away. A language for this is to be orchestrieren BPEL, which permits it.

Extensions

With the Web services Composite Application Framework (WS-CAF) a resuming specification was submitted with the W3C and with OASIS for standardisation, the Web services over for the co-ordination of applications useful standards, like e.g. Transaction management, to extend are. Further, extensions are angedacht with different manufacturers. In order to meet problems of security, concepts on the basis of the Security Assertion Markup LANGUAGE (SAML) are developed.

Literature

• Wolfgang DOS valley, Mario Jeckle, Ingo Melzer, Barbara Zengler: Service-oriented architectures with Web services. Spectrum academic publishing house, September 2005, ISBN 3-8274-1457-1 (Website to the book)
• Michael Kuschke, Ludger Web services compactly. Spectrum Akadademi publishing house, Heidelberg Berlin 2002, ISBN 3-8274-1375-3 (great an entrance for the beginner on 110 sides)
• Gustavo Alonso, F. Casati, H. Kuno: Web services. Springer, Berlin 2003, ISBN 3-540-44008-9 (English)
• Sanjiva Weerawarana, F. Curbera, F. Leymann: Web services Platform Architecture. Prentice resound to PTR, Upper Saddle River/NJ 2005, ISBN 0-13-148874-0 (English)

See also

• SOAP
• WSCI
• WSDL
• WSEL
• WSFL
• WSS
• UDDI
• BPEL
• Apache_Axis
• Service (computer science)

Related links

• Sides of the W3C over Web services
• German translations of the W3C specifications: edition-W3C
• Web services with Java, Axis, XDoclet and Eclipse
• Web services in the GI-encyclopedia
• XML protocol activity (English)
• Compilation of most diverse manufacturer definitions to the term Web service
• Web services and service Oriented Architectures. Definitions and explanations (English)
• German-language guidances: Amazon Web services and Google Web APIs
• Introduction to XML Webdienste

Search machines APIs

• API to Google
• API to Yahoo
• Project side with demo implementations to the Google Web APIs

Articles in category "Web service"

We found here 8 articles.

Related Websites

We found here 3 related websites.

• MSDN Web Services Developer Center
  The developer's home for information and resources about Web services, Indigo, .NET remoting, and other distributed technologies.


• Web Services Activity
  W3C's overview of news, groups, documents and specifications, events and recommended reading.


• Web Services Description Language (WSDL)
  The W3C note is a specification for describing network services as a set of endpoints operating on...