Page 205 - DCAP312_WEB_TECHNOLOGIES_II

Unit 10: Web Services

Notes
Figure10.1: Web Services

2
Web
1 Services 3
Bridge
Standardized
business request 4 Business
process
Standard protocol
5
Standardized
business response

The concepts used in Web Services hinge on the three following acronyms:
• SOAP (Simple Object Access Protocol) is a protocol based on the language, XML. It allows
exchanges between applications, whatever their platform. A SOAP service call is a stream
of ASCII text framed by XML tags and transported in the HTTP protocol.
• Web Services (Description Language) describes the Web Services in XML format, specifying
the methods that can be called, their signatures, and their access points (URL, port, etc.). To
some extent, it is the equivalent of CORBA's IDL language for distributed programming.
• UDDI (Universal Discovery Description and Integration) standardizes the use of distributed
directories for Web Services, allowing both publishing and discovery. UDDI behaves like
a Web Service itself, its methods being called using the SOAP protocol.
A significant advantage of Web Services, relative to other distributed architectures, is the support
of firewalls. By using the HTTP protocol on port 80, which is generally not secured, the Web
Services can get into the enterprise without being blocked by firewalls.

However, this creates other safety concerns because the default use of these characteristics is
too permissive. It is necessary to take this into account at the protocol levels.

A Web Service Example
In the following example we will use ASP.NET to create a simple Web Service that converts the
temperature from Fahrenheit to Celsius, and vice versa:
<%@ WebService Language= “VBScript” Class= “TempConvert” %>
Imports System
Imports System.Web.Services
Public Class TempConvert :Inherits WebService
<WebMethod()> Public Function FahrenheitToCelsius
(ByVal Fahrenheit As String) As String
dim fahr
fahr=trim(replace(Fahrenheit, “, “, “.”))
if fahr= ““ or IsNumeric(fahr)=false then return “Error”
return ((((fahr) - 32) / 9) * 5)
End function
<WebMethod()> Public Function CelsiusToFahrenheit
(ByVal Celsius As String) As String
dim cel

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