webservices

1. What are Windows services?

Windows services, previously known as NT services, are applications that are installed on the system as system services. In other words, Windows services are applications that run in the background with the Windows operating system. The primary use of Windows services is to reduce the consumption of memory required for performing backend operations. Let's take an example to understand this easily. Suppose you want to perform a variety of functions, such as monitor the performance of your computer or application, check the status of an application, and manage various devices, such as printers.

        In such a case, you can use Windows services to reduce memory consumption. In addition, Windows services can run on your system even if you have not logged on to your computer. In addition, these services do not have any user interface.

2. Can you share a process between Windows services?

Yes, you can share a process between Windows services.

3. In .NET, which is the parent class to create all Windows services?

The ServiceBase class is the parent class to create all Windows services.

4. Which class in .NET is used to install a Windows service?

The ServiceInstaller class, also known as the project installer class, is used to install a Windows service.

5. While installing a Windows service, an EventLogInstaller class is automatically created to install the event log related to the particular service. Is it true?

Yes, it is true.

6. Which property of the ServiceBase class can be used to specify whether a service can be paused and resumed?

The CanPauseAndContinue property provides such type of service.

7. Describe the services that UDDI provides to Web applications.

UDDI provides the following types of services to a Web application:

• XML Schema for business descriptions - Includes information about the service publisher (contact name, address, and so on) and specifications on the Web service
• Web registry of Web services - Includes business, service, and binding information for the Web service

8. Write the file extension for a Web service.

A Web service file extension is .asm file. For example, service1.asmx is a Web service file.

9. Which method is used to uninstall the Windows services?

The Uninstall() method is used to uninstall the Windows services.

10. What is the use of the mustUnderstand attribute in the Header element of a SOAP message?

The mustUnderstand attribute indicates that a header entry is either required or optional for the recipient to process further.

11. Explain the WSDL.

WSDL is a short form for Web Services Description Language, which is used to describe a Web service in terms of the messages that it creates and accepts. The WSDL document is an XML file that contains the interface schema for the Web service. It identifies the methods that are used during the exchange between a Web service consumer and a Web service provider. The following are the elements contained in the WSDL document:

• Types - Describe the variations of data types that are used to exchange messages between the user and the provider.
• Message - Describes the actual message or method call.
• portType - Describes the set of operations and each related message.
• binding - Describes the protocol details.
• service - Used to make groups a set of related ports together.

12. What advantage UDDI has over DISCO?

The UDDI directory has an advantage over a DISCO file, as it provides a single location where a client can find the Web services offered by different organizations.

13. How can you ensure that only authorized users access your Web service?

You should use the <authorization> element to ensure that only authorized users access your Web service. This element allows or denies access to your Web service according to their role.

14. Describe the EventLog class.

The EventLog class is used to access the Windows event logs from Windows services. Using EventLog, you can also customize Windows event logs that record information about important software and hardware events, such as the events of the .NET controls, keyboard, or other hardware devices.
           The EventLog class allows you to read or write to event logs, delete logs, and create as well as delete event sources. You can use the EventLog class to create event logs while creating an event source. An event source can be used to write to only one event log at a particular time. However, it is possible to associate one event log to multiple sources.

15. How can you prevent your Web services from unauthorized access?

The following are the ways to prevent your Web service from unauthorized access:

• Using encryption and message-based security.
• Using authentication and access controls for the Web service.

16. Explain the concept of Web services in brief.

A Web service may be defined as an independent and self-sustained unit of a software application that is hosted on the Web and implement specific functionalities to execute the business logic. A Web service provides so many functionalities, such as generating pay slips for employees, computing tax, broadcasting weather report, and providing updated news. The Web service allows application to share information or exchange data with other applications across different operating systems and hardware.

Therefore, the work of a Web service is to unite software by exchanging data irrespective of their operating systems, supported hardware, and programming language used in their development. The Web services transfer data in the XML format and use Simple Object Access Protocol (SOAP) to communicate. It is an XML based protocol. The Web services use Web Services Description Language (WSDL) and Universal Description, Discovery, and Integration (UDDI) to describe itself.

17. What advantages have Web services over Component Object Model (COM) and Distributed Component Object Model (DCOM)?

The advantages of Web services over COM and DCOM are as follows:

• Web services are simple to use and can be implemented on varied platforms.
• Web services are loosely coupled; as a result, their interfaces and methods can be extended.
• Web services do not carry any state information with them so that multiple requests can be processed simultaneously.

18. Mention the namespace that you must import in code to build a Web service.

System.Web.Services is the elementary namespace, which must be imported to develop code of a Web service.

19. What does the portType element of a WSDL document contain?

The portType element contains the operations exposed by the Web service, and the messages involved in the communication between the Web service and its consumers.

20. What is DISCO?

DISCO is a technology developed by Microsoft to publish and discover Web services. It discovers URLs of all XML Web services located on a Web server and creates a list of these Web services in a file called as a DISCO file.

21. Which two methods are used to discover the URL of Web services?

The two methods to discover the URL of Web services are Web service discovery tool (Disco.exe) and UDDI.

22. Which step is necessary to perform before a Web service can be consumed?

It is necessary to build a proxy class by using the wsdl.exe utility before a Web service can be consumed.

23. Which property of the WebMethod attribute allows you to maintain the state of objects across sessions in a Web method?

The WebMethod attribute's EnableSession property enables you to enable session state for a Web method.

24. Write the names of public properties defined in the WebService class.

There are many properties defined in the WebServices class:

• Application - Obtains the application object for the current HTTP request
• Context - Obtains the HttpContext object for the current request, which encapsulates all HTTP-specific context used by the HTTP server to process Web requests
• Server - Obtains the HttpServerUtility object for the current request
• Session - Obtains the HttpSessionState object for the current request
• SoapVersion - Obtains the version of the SOAP protocol used to make the SOAP request to a Web service
• User - Obtains the Server User Object. This property can be used to authenticate whether a user is authorized to execute the request.

     25. What do you understand by SOAP encoding?

        The Serialization of the types, such as integers and strings, inside a SOAP message is called encoding. The SOAP objects use XML elements and attributes to serialized data, for example, encodingStyle is an attribute of the Envelop element, which is used to specify the encoding rules for a SOAP object.

       26. What is the use of a .disco file?

        A client application uses a .disco file to locate or discover the documents that contain the description of a Web service. The .disco file contains links to other resources, which describe essential features, such as capabilities of a Web service. The links contained in a .disco file can refer to other discovery documents or XSD schemas. The description about the services and capabilities of a Web service is written in Web services Description Language (WSDL). A .disco file can also contain the information about other XML Web services that reside on the same or a different Web server.

        27. Mention the name of the directory where it is necessary to locate the proxy file to use a Web service.

         The proxy file must be stored in the /bin directory. This directory is situated under the root directory of the application.

         28. Does a Web service have state?

         The Web services do not have any technique to maintain state. However, it can access ASP.NET objects, such as application and session if they extend from the WebService base class.

        29. Which namespace must be included in a code that enables a XML Web service to write events in an event log file?

       The System.Diagnostics is the namespace, which must be included in a code to enable a Web service for writing events in an event log file.

        30. Which tool installs the DLL on your local computer and installs the Windows service in a transactional manner?

      The Installutil.exe tool.