Different books and different organizations provide different definitions to Web Services. Some of them are listed here.
A web service is any piece of software that makes itself available over the internet and uses a standardized XML messaging system. XML is used to encode all communications to a web service. For example, a client invokes a web service by sending an XML message, then waits for a corresponding XML response. As all communication is in XML, web services are not tied to any one operating system or programming language--Java can talk with Perl; Windows applications can talk with Unix applications.
Web services are self-contained, modular, distributed, dynamic applications that can be described, published, located, or invoked over the network to create products, processes, and supply chains. These applications can be local, distributed, or web-based.
Web services are built on top of open standards such as TCP/IP, HTTP, Java, HTML, and XML.
Web services are XML-based information exchange systems that use the Internet for direct application-to-application interaction. These systems can include programs, objects, messages, or documents.
A web service is a collection of open protocols and standards used for exchanging data between applications or systems. 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 inter-probability (e.g., between Java and Python, or Windows and Linux applications) is due to the use of open standards.
To summarize, a complete web service is, therefore, any service that:
the following Is available over the Internet or private (intranet) networks
Uses a standardized XML messaging system
Is not tied to any one operating system or programming language
Is self-describing via a common XML grammar
Is discoverable via a simple find mechanism
Components of Web Services
The basic web services platform is XML + HTTP. All the standard web services work using the following components
SOAP (Simple Object Access Protocol)
UDDI (Universal Description, Discovery and Integration)
WSDL (Web Services Description Language)
All these components have been discussed in the Web Services Architecture chapter.
How Does a Web Service Work?
A web service enables communication among various applications by using open standards such as
HTML, XML, WSDL, and SOAP. A web service takes the help of:
XML to tag the data
SOAP to transfer a message
WSDL to describe the availability of service.