A Web Service is programmable application logic accessible using standard Internet protocols. Web Services combine the best aspects of component-based development and the Web. Like components, Web Services represent black-box functionality that can be reused without worrying about how the service is implemented. Unlike current component technologies, Web Services are not accessed via object-model-specific protocols, such as DCOM, RMI, or IIOP. Instead, Web Services are accessed via ubiquitous Web protocols (ex: HTTP) and data formats (ex: XML).

Web Services is the next "big thing" in software development. Every business will eventually become both a supplier and consumer of Web Services. Web Services will completely change the way we conduct business, far beyond the impact we've seen with e-commerce. Web Services take what HTML and TCP/IP started, and add the element of XML, to enable task-focused services that come together dynamically over the Web.

Web Services are “Libraries” providing data and services to other applications over Web through a consistent set of interfaces and protocols.

Web Services are a new breed of Web application. They are self-contained, self-describing, modular applications that can be published, located, and invoked across the Web. Web Services perform functions, which can be anything from simple requests to complicated business processes. Once a Web service is deployed, other applications (and other Web Services) can discover and invoke the deployed service.

Web Services is a term that is being used to define a set of technologies that exposes business functionality over the Web as a set of automated interfaces. These automated interfaces allow businesses to discover and bind to interfaces at run-time, supposedly minimizing the amount of static preparation that is needed by other integration technologies.

SOAP & XML are core technologies of Web Services architecture.

Web Services and Enterprise Application Integration (EAI) are sometimes misunderstood to be one and the same. However, EAI tends to be more specific to a particular business process, such as connecting a specific order processing application to a specific inventory control application. And also, EAI is typically designed as a much tighter bound implementation of connecting systems. Web Services are a loose bound collection of services & they are much easy to plug in & out, discover, and bind to dynamically.

To summarize: a Web Service is

• A programmable application, accessible as a component via standard Web protocols,
• Uses standard Web protocols like HTTP, XML and SOAP,
• Works through existing proxies and firewalls,
• Can take advantage of HTTP authentication,
• Encryption for free with SSL,
• Easy incorporation with existing XML messaging solutions,
• Takes advantage of XML messaging schemas and easy transition from XML RPC solutions,
• No conflict between proprietary component based solutions like CORBA and COM,
• Combines the best aspects of component–based development and the Web, and
• Available to a variety of clients (platform independent).

In a nutshell, a Web Service is an application that can be called over the Web using standards such as SOAP over HTTP.

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