Web Service Interview Questions

What is a Web service?

Many people and companies have debated the exact definition of Web services. At a minimum, however, 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. Because 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.
What is new about Web services?

People have been using Remote Procedure Calls (RPC) for some time now, and they long ago discovered how to send such calls over HTTP.

I keep reading about Web services, but I have never actually seen one. Can you show me a real Web service in action?

If you want a more intuitive feel for Web services, try out the IBM Web Services Browser, available on the IBM Alphaworks site. The browser provides a series of Web services demonstrations.

Behind the scenes, it ties together SOAP, WSDL, and UDDI to provide a simple plug-and-play interface for finding and invoking Web services.

For example, you can find a stock-quote service, a traffic-report service, and a weather service. Each service is independent, and you can stack services like building blocks. You can, therefore, create a single page that displays multiple services--where the end result looks like a stripped-down version of my.yahoo or my.excite.
What is the Web service protocol stack?
The Web service protocol stack is an evolving set of protocols used to define, discover, and implement Web services.

The core protocol stack consists of four layers: Service Transport: This layer is responsible for transporting messages between applications. Currently, this includes HTTP, SMTP, FTP, and newer protocols, such as Blocks Extensible Exchange Protocol (BEEP). XML Messaging: This layer is responsible for encoding messages in a common XML format so that messages can be understood at either end. Currently, this includes XML-RPC and SOAP. Service Description: This layer is responsible for describing the public interface to a specific Web service. Currently, service description is handled via the WSDL. Service Discovery: This layer is responsible for centralizing services into a common registry, and providing easy publish/find functionality. Currently, service discovery is handled via the UDDI. Beyond the essentials of XML-RPC, SOAP, WSDL, and UDDI, the Web service protocol stack includes a whole zoo of newer, evolving protocols. These include WSFL (Web Services Flow Language), SOAP-DSIG (SOAP Security Extensions: Digital Signature), and USML (UDDI Search Markup Language). For an overview of these protocols, check out Pavel Kulchenko's article, Web Services Acronyms, Demystified, on XML.com. Fortunately, you do not need to understand the full protocol stack to get started with Web services. Assuming you already know the basics of HTTP, it is best to start at the XML Messaging layer and work your way up.
What is SOAP?

SOAP is an XML-based protocol for exchanging information between computers. Although SOAP can be used in a variety of messaging systems and can be delivered via a variety of transport protocols, the main focus of SOAP is Remote Procedure Calls (RPC) transported via HTTP. Like XML-RPC, SOAP is platform independent, and therefore enables diverse applications to communicate with one another.
What is WSDL?
The Web Services Description Language (WSDL) currently represents the service description layer within the Web service protocol stack. In a nutshell, WSDL is an XML grammar for specifying a public interface for a Web service. This public interface can include the following: Information on all publicly available functions. Data type information for all XML messages. Binding information about the specific transport protocol to be used. Address information for locating the specified service. WSDL is not necessarily tied to a specific XML messaging system, but it does include built-in extensions for describing SOAP services.
What is UDDI?

UDDI (Universal Description, Discovery, and Integration) currently represents the discovery layer within the Web services protocol stack. UDDI was originally created by Microsoft, IBM, and Ariba, and represents a technical specification for publishing and finding businesses and Web services. At its core, UDDI consists of two parts.

First, UDDI is a technical specification for building a distributed directory of businesses and Web services. Data is stored within a specific XML format, and the UDDI specification includes API details for searching existing data and publishing new data. Second, the UDDI Business Registry is a fully operational implementation of the UDDI specification. Launched in May 2001 by Microsoft and IBM, the UDDI registry now enables anyone to search existing UDDI data. It also enables any company to register themselves and their services.
How do I get started with Web Services?

The easiest way to get started with Web services is to learn XML-RPC. Check out the XML-RPC specification or read my book, Web Services Essentials. O'Reilly has also recently released a book on Programming Web Services with XML-RPC by Simon St.Laurent, Joe Johnston, and Edd Dumbill. Once you have learned the basics of XML-RPC, move onto SOAP, WSDL, and UDDI. These topics are also covered in Web Services Essentials. For a comprehensive treatment of SOAP, check out O'Reilly's Programming Web Services with SOAP, by Doug Tidwell, James Snell, and Pavel Kulchenko.
Does the W3C support any Web service standards?

The World Wide Web Consortium (W3C) is actively pursuing standardization of Web service protocols. In September 2000, the W3C established an XML Protocol Activity. The goal of the group is to establish a formal standard for SOAP. A draft version of SOAP 1.2 is currently under review, and progressing through the official W3C recommendation process. On January 25, 2002, the W3C also announced the formation of a Web Service Activity.

This new activity will include the current SOAP work as well as two new groups. The first new group is the Web Services Description Working Group, which will take up work on WSDL. The second new group is the Web Services Architecture Working Group, which will attempt to create a cohesive framework for Web service protocols.
Which one is better Remoting or WebServices ?

Remoting involves efficient communication or exchange of data when we have control on both ends of the application involved in the communication process. Web Services is open-protocol-based exchange of informaion. Web Services play there role when we need to communicataion with external organization or whicj doesnot have .NET technology. ..