Web services are components on a Web server that a client application can call by making HTTP requests across the Web. ASP.NET enables you to create custom Web services or to use built-in application services, and to call these services from any client application. Basically 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.
In simple sense, Web Services are means for interacting with objects over the Internet. The Web serivce consumers are able to invoke method calls on remote objects by using SOAP and HTTP over the Web. WebService is language independent and Web Services communicate by using standard web protocols and data formats, such as :
You can use Weather Reporting web service to display weather information in your personal website.
You can display latest update of Share market with Stock Quote on your web site
You can display latest news update by using News Headline Web Service in your website.
Web Service Properties
First, a Web service can have a public interface, defined in a common XML grammar. The interface describes all the methods available to clients and specifies the signature for each method. Currently, interface definition is accomplished via the Web Service Description Language (WSDL).
Second, if you create a Web service, there should be some relatively simple mechanism for you to publish this fact. Likewise, there should be some simple mechanism for interested parties to locate the service and locate its public interface. The most prominent directory of Web services is currently available via UDDI, or Universal Description, Discovery, and Integration.
Web Service Advantages
Since Web services are platform & language independent, hence any web services from different sources can communicate to one another.
Web Service messages are formatted as XML and this message is sent via HTTP, so that they can reach to any machine on the internet without being blocked by firewall.