A web service is a service offered by an electronic device to another electronic device, communicating with each other via the World Wide Web. In a web service, the Web technology such as HTTP—originally designed for human-to-machine communication—is utilized for machine-to-machine communication, more specifically for transferring machine-readable file formats such as XML and JSON. In practice, a web service typically provides an Object database web-based interface to a database server, utilized for example by another web server, or by a mobile app, that provides a user interface to the end user. Another common application offered to the end user may be a mashup, where a web server consumes several web services at different machines, and compiles the content into one user interface.
The W3C defines a web service generally as:
Web services may use SOAP over HTTP protocol, allowing less costly (more efficient) interactions over the Internet than via proprietary solutions like EDI/B2B. Besides SOAP over HTTP, web services can also be implemented on other reliable transport mechanisms like FTP. In a 2002 document, the Web Services Architecture Working Group defined a web services architecture, requiring a standardized implementation of a "web service." In this:
In a 2004 document, the W3C extended the definition:
The term "web service" describes a standardized way of integrating web-based applications using the XML, SOAP, WSDL and UDDI open standards over an Internet Protocol backbone. XML is the data format used to contain the data and provide metadata around it, SOAP is used to transfer the data, WSDL is used for describing the services available and UDDI lists what services are available.
A web service is a method of communication between two electronic devices over a network. It is a software function provided at a network address over the web with the service always on as in the concept of utility computing.
Many organizations use multiple software systems for management. Different software systems often need to exchange data with each other, and a web service is a method of communication that allows two software systems to exchange this data over the internet. The software system that requests data is called a service requester, whereas the software system that would process the request and provide the data is called a service provider.
Different software may use different programming languages, and hence there is a need for a method of data exchange that doesn't depend upon a particular programming language. Most types of software can, however, interpret XML tags. Thus, web services can use XML files for data exchange.
Rules for communication between different systems need to be defined, such as:
All of these rules for communication are defined in a file called WSDL (Web Services Description Language), which has a .wsdl extension. (Proposals for Autonomous Web Services ( AWS) seek to develop more flexible web services which do not rely on strict rules.
A directory called UDDI (Universal Description, Discovery and Integration) defines which software system should be contacted for which type of data. So when one software system needs one particular report/data, it would go to the UDDI and find out which other system it can contact for receiving that data. Once the software system finds out which other system it should contact, it would then contact that system using a special protocol called SOAP (Simple Object Access Protocol). The service provider system would first validate the data request by referring to the WSDL file, and then process the request and send the data under the SOAP protocol.
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 model) or to generate a class skeleton given existing WSDL (a top-down model).
Critics of non-RESTful web services often complain that they are too complex and based upon large software vendors or integrators, rather than typical open source implementations.
Web services testing can also be automated using several test automation tools like SOAP UI, Oracle Application Testing Suite (OATS), Oracle Application Testing Suite Web Services Testing using Oracle Application Testing Suite Unified Functional Testing, Selenium, etc.