From http://www.w3schools.com (Copyright Refsnes Data)
Web services are small units of code built to handle a limited task.
Web services are small units of code designed to handle a limited set of tasks.
An example of a web service can be a small program designed to supply other applications with the latest stock exchange prices. Another example can be a small program designed to handle credit card payment.
Web services use the standard web protocols HTTP, XML, SOAP, WSDL, and UDDI.
HTTP (Hypertext Transfer Protocol) is the World Wide Web standard for communication over the Internet. HTTP is standardized by the World Wide Web Consortium (W3C).
XML (eXtensible Markup Language) is a well known standard for storing, carrying, and exchanging data. XML is standardized by the W3C.
You can read more about XML in our XML tutorial.
SOAP (Simple Object Access Protocol) is a lightweight platform and language neutral communication protocol that allows programs to communicate via standard Internet HTTP. SOAP is standardized by the W3C.
You can read more about SOAP in our SOAP tutorial.
WSDL (Web Services Description Language) is an XML-based language used to define web services and to describe how to access them. WSDL is a suggestion by Ariba, IBM and Microsoft for describing services for the W3C XML Activity on XML Protocols.
You can read more about WSDL in our WSDL tutorial.
UDDI (Universal Description, Discovery and Integration) is a directory service where businesses can register and search for web services.
UDDI is a public registry, where one can publish and inquire about web services.
Since web services use XML based protocols to communicate with other systems, web services are independent of both operating systems and programming languages.
An application calling a web service will always send its requests using XML, and get its answer returned as XML. The calling application will never be concerned about the operating system or the programming language running on the other computer.
Web services make it easier to communicate between different applications. They also make it possible for developers to reuse existing web services instead of writing new ones.
Web services can create new possibilities for many businesses because it provides an easy way to distribute information to a large number of consumers. One example could be flight schedules and ticket reservation systems.
From http://www.w3schools.com (Copyright Refsnes Data)