Page 217 - DCAP312_WEB_TECHNOLOGIES_II

Unit 10: Web Services

services use HTTP because it is ubiquitous. Since HTTP is a core protocol of the Web, most Notes
organizations have a network infrastructure that supports HTTP and people who understand
how to manage it already. The security, monitoring, and load-balancing infrastructure for HTTP
are readily available today.
10.2.2 WSDL

WSDL (often pronounced whiz-dull) stands for Web Services Description Language. For our
purposes, we can say that a WSDL file is an XML document that describes a set of SOAP
messages and how the messages are exchanged. In other words, WSDL is to SOAP what IDL
is to CORBA or COM. Since WSDL is XML, it is readable and editable but in most cases, it is
generated and consumed by software.
To see the value of WSDL, imagine you want to start calling a SOAP method provided by one
of your business partners. You could ask him for some sample SOAP messages and write your
application to produce and consume messages that look like the samples, but this can be error-
prone. For example, you might see a customer ID of 2837 and assume is an integer when in
fact it is a string. WSDL specifies what a request message must contain and what the response
message will look like in unambiguous notation.
The notation that a WSDL file uses to describe message formats is based on the XML Schema
standard which means it is both programming-language neutral and standards-based which
makes it suitable for describing XML Web services interfaces that are accessible from a wide
variety of platforms and programming languages. In addition to describing message contents,
WSDL defines where the service is available and what communications protocol is used to talk
to the service. This means that the WSDL file defines everything required to write a program
to work with an XML Web service. There are several tools available to read a WSDL file and
generate the code required to communicate with an XML Web service. Some of the most capable
of these tools are in Microsoft Visual Studio .NET.

10.2.3 UDDI
Universal Discovery Description and Integration (UDDI) is the yellow pages of Web services.
You can, of course, offer a Web service without registering it in UDDI, just as you can open a
business in your basement and rely on word-of-mouth advertising but if you want to reach a
significant market, you need UDDI so your customers can find you.
A UDDI directory entry is an XML file that describes a business and the services it offers. There
are three parts to an entry in the UDDI directory. The “white pages” describe the company
offering the service: name, address, contacts, etc. The “yellow pages” include industrial categories
based on standard taxonomies such as the North American Industry Classification System and
the Standard Industrial Classification. The “green pages” describe the interface to the service
in enough detail for someone to write an application to use the Web service. The way services
are defined is through a UDDI document called a Type Model or t-Model. In many cases, the
t-Model contains a WSDL file that describes a SOAP interface to an XML Web service, but the
t-model is flexible enough to describe almost any kind of service.
10.2.4 General Principles of Web Services XML

The general principles are given as:
Principle of Core Content
If you consider the information in question to be part of the essential material that is being
expressed or communicated in the XML, put it in an element. For human-readable documents this
generally means the core content that is being communicated to the reader. For machine-oriented
records formats this generally means the data that comes directly from the problem domain.

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