WCF Interview Questions and Answers

Answer - 1 : - Windows Communication Foundation (WCF) is a framework for building service-oriented applications. Using WCF, you can send data as asynchronous messages from one service endpoint to another. A service endpoint can be part of a continuously available service hosted by IIS, or it can be a service hosted in an application. An endpoint can be a client of a service that requests data from a service endpoint. The messages can be as simple as a single character or word sent as XML, or as complex as a stream of binary data. A few sample scenarios include: A secure service to process business transactions. A service that supplies current data to others, such as a traffic report or other monitoring service. A chat service that allows two people to communicate or exchange data in real time. A dashboard application that polls one or more services for data and presents it in a logical presentation. Exposing a workflow implemented using Windows Workflow Foundation as a WCF service. A Silverlight application to poll a service for the latest data feeds. While creating such applications was possible prior to the existence of WCF, WCF makes the development of endpoints easier than ever. In summary, WCF is designed to offer a manageable approach to creating Web services and Web service clients

Answer - 2 : - WCF includes the following set of features. Service Orientation One consequence of using WS standards is that WCF enables you to create service oriented applications. Service-oriented architecture (SOA) is the reliance on Web services to send and receive data. The services have the general advantage of being loosely-coupled instead of hard-coded from one application to another. A loosely-coupled relationship implies that any client created on any platform can connect to any service as long as the essential contracts are met. Interoperability WCF implements modern industry standards for Web service interoperability. For more information about the supported standards, see Interoperability and Integration. Multiple Message Patterns Messages are exchanged in one of several patterns. The most common pattern is the request/reply pattern, where one endpoint requests data from a second endpoint. The second endpoint replies. There are other patterns such as a one-way message in which a single endpoint sends a message without any expectation of a reply. A more complex pattern is the duplex exchange pattern where two endpoints establish a connection and send data back and forth, similar to an instant messaging program. For more information about how to implement different message exchange patterns using WCF. Service Metadata WCF supports publishing service metadata using formats specified in industry standards such as WSDL, XML Schema and WS-Policy. This metadata can be used to automatically generate and configure clients for accessing WCF services. Metadata can be published over HTTP and HTTPS or using the Web Service Metadata Exchange standard. Data Contracts Because WCF is built using the .NET Framework, it also includes code-friendly methods of supplying the contracts you want to enforce. One of the universal types of contracts is the data contract. In essence, as you code your service using Visual C# or Visual Basic, the easiest way to handle data is by creating classes that represent a data entity with

Answer - 3 : - ServiceBehaviour attribute is used to specify the InstanceContextMode for the WCF Service class (This can be used to maintained a state of the service or a client too) There are three instance Context Mode in the WFC PerSession : This is used to create a new instance for a service and the same instance is used for all method for a particular client. (eg: State can be maintained per session by declaring a variable) PerCall : This is used to create a new instance for every call from the client whether same client or different. (eg: No state can be maintained as every time a new instance of the service is created) Single : This is used to create only one instance of the service and the same instance is used for all the client request. (eg: Global state can be maintained but this will be applicable for all clients)

Answer - 4 : - SOA is Service Oriented Architecture. SOA service is the encapsulation of a high level business concept. A SOA service is composed of three parts. 1. A service class implementing the service to be provided. 2. An environment to host the service. 3. One or more endpoints to which clients will connect.

Answer - 5 : - Self hosting the service in his own application domain. This we have already covered in the first section. The service comes in to existence when you create the object of ServiceHost class and the service closes when you call the Close of the ServiceHost class. Host in application domain or process provided by IIS Server. Host in Application domain and process provided by WAS (Windows Activation Service) Server.

Answer - 6 : - We Should remember ABC. Address --- Specifies the location of the service which will be like http://Myserver/MyService.Clients will use this location to communicate with our service. Binding --- Specifies how the two paries will communicate in term of transport and encoding and protocols Contract --- Specifies the interface between client and the server.It's a simple interface with some attribute.

Answer - 7 : - Web services can only be invoked by HTTP (traditional webservice with .asmx). While WCF Service or a WCF component can be invoked by any protocol (like http, tcp etc.) and any transport type. Second web services are not flexible. However, WCF Services are flexible. If you make a new version of the service then you need to just expose a new end. Therefore, services are agile and which is a very practical approach looking at the current business trends. We develop WCF as contracts, interface, operations, and data contracts. As the developer we are more focused on the business logic services and need not worry about channel stack. WCF is a unified programming API for any kind of services so we create the service and use configuration information to set up the communication mechanism like HTTP/TCP/MSMQ etc    

Answer - 8 : - There are three major ways of hosting a WCF services • Self-hosting the service in his own application domain. This we have already covered in the first section. The service comes in to existence when you create the object of Service Host class and the service closes when you call the Close of the Service Host class. • Host in application domain or process provided by IIS Server. • Host in Application domain and process provided by WAS (Windows Activation Service) Server. More details http://www.dotnetfunda.com/articles/article221.aspx#whatarethevariouswaysofhostingaWCFservice