vb .net tutorial - 15

8/14/2019 VB .net tutorial - 15

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Creating and Using Web Services

NIIT Creating and Using Web Services/Lesson 15/Slide 1 of 28

Objectives

In this lesson, you will learn to:

Identify the need for Web services

Identify the enabling technologies in Web services

Create a Web service

Use a Web service in a Visual Basic .NET local application

Use a Web service in a Web application


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Web Service

Is similar to a component that provides a specific

functionality.

Exposes a number of methods that provide functionality thatcan be used by one or more applications, regardless of the

programming languages, operating systems, and hardware

platforms used to develop them.

Functionality can be accessed by applications by usingInternet standards, such as HTTP and XML.


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Web Service (Contd.)

Can be of different types:

One that provides a fundamental functionality, which

can be used in multiple applications.

Second that can integrate the existing applications that

might have been created using different software and

hardware platforms.

Third that can be a means to exchange data in

business-to-business transactions.


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Enabling Technologies Used in Web Services

A Web service can be developed by using any

programming language in .NET suite. However, it requires:

A common data representation format in order to ensurethe interoperability of the data exchanged by the client

application and the Web service.

A standard method for sending messages from the

client application to the Web service and vice versa.

A standard format for describing the Web service.

A mechanism to allow client applications to discover the

Web services and their locations.


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Enabling Technologies Used in Web Services(Contd.)

Requirements are fulfilled by using various standards

such as: eXtensible Markup Language (XML) - Allows data

interchange regardless of the hardware and software

platform used to develop the application.

Simple Object Access Protocol (SOAP) - Is a standard

communication protocol for interchanging information in

a structured format in a distributed environment.

Web Services Description Language (WSDL) Is an

XML vocabulary that describes the methods that are

exposed by a Web service.


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Enabling Technologies Used in Web Services(Contd.)

Universal Description Discovery and Integration (UDDI)

- Is used as a standard mechanism to register anddiscover a Web service provided by various Web

service providers.


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Just a Minute

What is the difference between a Web service and a

component?


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Problem Statement 15.D.1

The Call Center application needs to provide a facility for

various departments to view the status of the queries received

from various customers. The organization also plans to

provide a facility to its customers to find out the status of their

queries through a Web site. For this, a reusable code needs to

be written so that both local and Web applications can access

the details about queries.


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Task List

Identify a mechanism for writing reusable code.

Identify the methods to be exposed to applications.

Create a Web service project.

Create the methods to be exposed to applications.

Execute the application.


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Task 1: Identify a mechanism for writing reusablecode.

Result:

A Web service allows applications to transfer data by usingstandard protocols and data formats. Therefore, in the given

scenario, you can create a Web service that exposes a Web

method to access query details.


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Task 2: Identify the methods to be exposed toapplications.

Result:

In the given scenario, you need to create a Web service andexpose a Web method that takes a query ID as a

parameter. The Web method should retrieve the details

about the query and populate a DataSet object with the

query details. This DataSet object should be returned to theclient application that uses the Web service.


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Task 3: Create a Web service project.

Task 4: Create the methods to be exposed to

applications.

Code model for Web services

A Web service is composed of two parts, the Web

service entry point and the code that provides the

functionality to be used by other applications.

The .asmx file serves as the entry point for the Web

service.

The .asmx file accesses the code from precompiled

assemblies and the code-behind (.vb) filecorresponding to the Web service.


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The code-behind file imports theSystem.Web.Services namespace, which contains

the classes that are required to build and use Web

services.

All Web service classes inherit the WebService class,

which belongs to the System.Web.Services

namespace.

While writing code within the Web service class, you

can use the following attributes:

WebService: Used to provide additional information

about the Web methods exposed by a Web service.

WebMethod: Used for every method that needs tobe exposed for use by other applications.


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Task 5: Execute the application.


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Problem Statement 15.D.2

A form needs to be designed in the Call Center application to

display the details about a query. The code for retrieving the

details about a query is provided in the GetQueryData Web

service. This Web service needs to be used in the Call Center

application to enable various departments of Diaz

Telecommunications to view the status of queries.


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Task List

Identify the data to be displayed.

Design the user interface.

Write the code to display data by using the functionality

exposed by the Web service.

Execute the application.


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Task 1: Identify the data to be displayed.

Result:

The data to be displayed includes:

Query ID

Date of submission

Customer ID

Employee ID

Response date

Status

Feedback


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Task 2: Design the user interface.

Task 3: Write the code to display data by using the

functionality exposed by the Web service.

To access the functionality exposed by a Web service,perform the following tasks:

Locate the Web service that provides the functionality

required in the application.

Create a proxy class for the Web service.

Reference the proxy class in the application code.

Instantiate the proxy class.


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Task 4: Execute the application.


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Just a Minute

2. How can you locate the Web services developed by a Web

service provider?

3. Which attribute is used to describe a Web service?


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ASP.NET

Is a powerful programming framework for the development

of enterprise-class Web applications.

Is a part of the .NET Framework.

Provides access to all the features of the .NET Framework.

Therefore, you can develop an ASP.NET Web application

by using any of the programming languages provided in .

NET, such as Visual Basic .NET and C#.


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Elements of ASP.NET

User interface - For accepting input and displaying text to a

user in an ASP.NET Web application, Web Formsare used.

The working of a Web Form is similar to that of a Windows

Form except that the user interface is typically rendered in a

Web browser.

Components For providing reusable code and adding

business logic in an ASP.NET Web application, Web

services are used.

Data - For accessing data stored in a database in an

ASP.NET Web application, ADO.NET is used.


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Web Form

Allows you to create programmable Web pages that serve

as a user interface for your Web application.

Provides a combination of HTML, various Web Formcontrols, and code. Code provided in a Web Form is

executed on a Web server running Internet Information

Services (IIS) 5.0.

Can be used to interact with any Web application regardlessof the browser or the type of computer used by them.


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Summary

In this lesson, you learned that:

A Web service exposes functionality that can be used by

one or more applications, regardless of theprogramming languages, operating systems, and hardware

platforms used to develop them.

The functionality exposed by a Web service can be

accessed by applications by using Internet standards, suchas HyperText Transfer Protocol (HTTP) and eXtensible

Markup Language (XML).

A Web service can be created using any programming

language in .NET suite, such as Visual Basic .NET, VisualC#.NET, and Visual C++.NET.


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Summary (Contd.)

Web services use eXtensible Markup Language for

interchanging data in a standard format between different

applications.

To be able to communicate with each other, a Web service

and a client application must agree upon a common

protocol. SOAP is a standard communications protocol

for interchanging information in a structured format in a

distributed environment.

To be able to use a Web service, the developers of a client

application need to know the methods exposed by the

Web service and the parameters to be passed to thesemethods. Web Services Description Language (WSDL) is

a markup language, which is used to describe a Web

service.


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Summary (Contd.)The Universal Description Discovery and Integration (UDDI)

initiative is used to allow client applications to discoverthe Web services provided by various Web service

providers.A Web service consists of two parts, the Web service entry

point and the code that provides the functionality that isused by other applications.

The .asmx file serves as the entry point for the Web service.

The WebService attribute is an optional attribute that canbe used to provide additional information about the

Web methods exposed by a Web service.

You must place the WebMethod attribute before thedeclaration of every method that needs to be exposed foruse by other applications.


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Summary (Contd.)In order to be able to access the functionality exposed by a

Web service, you need to perform the following tasks:

Locate the Web service that provides the functionalityrequired in the application.

Create a proxy class for the Web service.

Reference the proxy class in the application code.

Instantiate the proxy class.

Visual Studio .NET provides you with an integrateddevelopment environment for creating Web applicationsranging from traditional Web sites consisting of several

HTML pages to sophisticated business-to-businessapplications that provide Web-based components forperforming data interchange between trading partners.


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Summary (Contd.)

The Web applications developed using Visual Studio.NET

are built on ASP.NET, which is a powerful

programming framework for the development of enterprise-

class Web applications.

ASP.NET is a part of the .NET Framework. It provides

access to all features of the .NET Framework.

An ASP.NET Web application has the same elements asany other client-server application. These elements are

the user interface, components, and data.

Web services can be effectively used in both local and Web

applications. Using a Web service in an ASP.NET Webapplication involves the same steps as in the case of a

Windows application.

vb .net tutorial - 15

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