Web Services

According to the W3C a Web service is a software system designed to support interoperable machine-to-machine interaction over a network. It has an interface that is described in a machine-processable format such as WSDL. Other systems interact with the Web service in a manner prescribed by its interface using messages, which may be enclosed in a SOAP envelope, or follow a REST approach. These messages are typically conveyed using HTTP, and normally comprise XML in conjunction with other Web-related standards. Software applications written in various programming languages and running on various platforms can use web services to exchange data over computer networks like the Internet in a manner similar to inter-process communication on a single computer. This interoperability (for example, between Java and Python, or Microsoft Windows and Linux applications) is due to the use of open standards. OASIS and the W3C are the primary committees responsible for the architecture and standardization of web services. To improve interoperability between web service implementations, the WS-I organization has been developing a series of profiles to further define the standards involved.

Standards used

• Web Services Protocol Stack: The Standards and protocols used to consume a web service, considered as a protocol stack.
• XML: All data to be exchanged is formatted with XML tags. The encoded message may conform to a messaging standard such as SOAP or the older XML-RPC. The XML-RPC scheme calls functions remotely, whilst SOAP favours a more modern (object-oriented) approach based on the Command pattern.
• Common protocols: data can be transported between applications using any number of common protocols, such as HTTP, FTP, SMTP and XMPP.
• WSDL: The public interface to the web service is described by Web Services Description Language, or WSDL. This is an XML-based service description on how to communicate using the web service.
• UDDI: The web service information is published using this protocol. It should enable applications to look up web services information in order to determine whether to use them.
• WS-Security: The Web Services Security protocol has been accepted as an OASIS standard. The standard allows authentication of actors and confidentiality of the messages sent.
• WS-ReliableExchange: A SOAP-based specification that fulfills reliable messaging requirements critical to some applications of Web Services. Accepted as an OASIS standard.
• WS-Management: This specification describes a SOAP-based protocol for systems managment of personal computers, servers, devices, and other manageable hardware and Web services and other applications.

Advantages of web services

• Web services provide interoperability between various software applications running on disparate platforms.
• Web services use open standards and protocols. Protocols and data formats are text-based where possible, making it easy for developers to comprehend.
• By utilizing HTTP, web services can work through many common firewall security measures without requiring changes to the firewall filtering rules.
• Web services easily allow software and services from different companies and locations to be combined easily to provide an integrated service.
• Web services allow the reuse of services and components within an infrastructure.

Disadvantages of web services

• Web services standards for features such as transactions are currently nonexistent or still in their infancy compared to more mature distributed computing open standards such as CORBA. This is likely to be a temporary disadvantage as most vendors have committed to the OASIS standards to implement the Quality of Service aspects of their products.
• Web services may suffer from poor performance compared to other distributed computing approaches such as RMI, CORBA, or DCOM. This is a common trade-off when choosing text-based formats. XML explicitly does not count among its design goals either conciseness of encoding or efficiency of parsing. This could change with the XML Infoset standard, which describes XML-based languages in terms of abstractions (elements, attributes, logical nesting). The traditional angle-bracket representation is now seen as an ASCII (or Unicode) serialisation of XML, not XML itself. In this model, binary serialisation is an equally valid alternative. Binary representations such as SOAP MTOM promise to improve the wire efficiency of XML messaging.

Platforms

Web services can be deployed by using application server software. A sample of application servers:

• Axis and the Jakarta Tomcat server (both at the Apache project)
• ColdFusion from Macromedia
• Cordys WS-AppServer
• infoRouter Document Management software Web Services API
• DotGnu from GNU Project
• Java Web Services Development Pack (JWSDP) from Sun Microsystems (based on Jakarta Tomcat)
• JOnAS (part of the ObjectWeb Open Source initiative)
• Mono development platform from Novell
• Microsoft .NET servers from Microsoft
• WebLogic from BEA Systems
• WebSphere Application Server from IBM (based on the Apache server and the J2EE platform)
• Zope is an object oriented web application server written in Python
• Web Application Server from SAP (the Web AS is a key part of the SAP NetWeaver stack)
• Pramati Application Server from Pramati Technologies Limited
• OpenEdge Platform from Progress Software
• Oracle Application Server from Oracle Corporation

Companies providing Web Services

These are companies that provide open public web services:

• Amazon.com - Search Products, Product Information, Cart System, Wish List
• eBay - Auction Search, Bidding, Auction Creation
• Google - In Beta - Web Search, Maps
• Yahoo! - Maps, Traffic
• FedEx - Tracking
• PayPal - Payment System
• Mappoint - Maps
• MSN - Virtual Earth
• BookBlog
• Flickr - Photo
• Interfax
• cddb
• Livejournal
• Blogger
• Xignite - Financial market data

See also

• List of Web service specifications

• Business logic
• Computing
• REST
• Service-oriented analysis and design
• Service-oriented architecture
• Software component
• Software design
• Web application
• Website

External links

• Apache Axis (SOAP Implementation)
• gSOAP: C/C++ Web Services and Clients
• Article, "Stop the hype about webservices!"
• XMethods listing of publicly available web services
• Microsoft proposed standards
• Organization for the Advancement of Structured Information Standards
• Web Services Activity at World Wide Web Consortium
• XML Protocol Working Group (SOAP) at World Wide Web Consortium
• Web Services Architecture at World Wide Web Consortium
• Articles, podcasts, webcasts about Web services security at WebServicesSummit.com
• Article, "The third era starts here"
• Service-Oriented Architecture (SOA) and Web services at IBM developerWorks.
• Oracle Web Services Technology Center
• Web services product information
• IEEE International Conference on Web Services
• IEEE International Conference on Services Computing
• International Journal of Web Services Research (JWSR)
• IEEE Services Computing Community
• Google Web APIs demo implementations
• Some sophisticated Web service interface specifications have been developed by the Open Geospatial Consortium (OGC)