Web service - Wikipedia

A Web Service is a string-based service (i.e. functionality) provided over the Internet, usually in a data language, meant as communication between computer software.

EDI was a precursor to web services, and is relatively difficult and expensive to implement, but reputedly reliable.

The World Wide Web Consortium has recognized that web services are an integral part of their work with XML and related technologies, and have several working groups appointed to the subject.

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1 Characteristics

2 Advantages of Web Services

3 Platforms

4 See also

5 Standards & Proposals

Characteristics

The communication between Web services are implemented in one of the standard Internet Protocols. The most common Protocol is HTTP, but others like EMail and FTP are possible.
XML is used for all communication purposes- for metadata WSDL is one of the more common formats, for data itself SOAP is dominant.
On top of those protocols sits another layer, which is in the process of being standardized. These protocols are embedded in SOAP and deal with transactions, security and relating of messages.

Protocols defined within the XML framework include the XML-RPC protocol for simple web services, and the SOAP and WSDL protocols for both simple and more complex web services. UDDI is for directories of services and RSS (Rich Site Summary) is an example of a very simple Web service. The composition of Web Services can be described by WSFL.

Advantages of Web Services

The main reason as to why Web Services are used seem to be that they rely on HTTP over TCP port 80. To understand this, keep in mind that many enterprises have protected themselves (see computer security) using firewalls, that filter and block much Internet traffic for security reasons. In this milieu, typically many ports, almost all, are closed to incoming and outgoing traffic, and the administrators of these firewalls are not eager to open them up to any traffic. However port 80 is always open, as it is used for web browsers, and thus, Web Services are appealing as they tunnel everything through port 80.

Another reason may be that prior to SOAP there were not really good interfaces to accessing functionality on different computers on a network, most of them were ad hoc and few people knew or could handle EDI, RPC and similar APIs. Web Services may have more solid frameworks and are thus easier to use.

Platforms

Web services usually run on dedicated computers called application servers. There are a few brands of these:

Websphere Application Server[?] from IBM (based on the Apache server and the J2EE platform)
WebLogic Application Server[?] from BEA[?]
Microsoft .NET servers from Microsoft

Standards & Proposals

Web Services Activity (http://www.w3.org/2002/ws/) at World Wide Web Consortium
XML Protocol Working Group (Soap) (http://www.w3.org/2000/xp/Group/)
List of Proposals by Microsoft (http://msdn.microsoft.com/webservices/understanding/gxa/)