What are Xml Web Services

1
What are Xml Web Services?

• A Web Service simply an application that exposes
  a Web-accessible API .
• Web services are a new, standard  platform for
  building interoperable distributed applications.
• The Web services platform is a set of standards
  that applications follow to achieve
  interoperability via the Web.
• You write your Web services in whatever language
  and on any platform you like, as long as those
  Web services can be viewed and accessed according
  to the Web services standards.

2
About Web Services

• Web Services, unlike DCOM or CORBRA, are founded
  on universal, nonproprietary standards including
  XML and HTTP and offer a model that is platform
  independent communicate using platform-independen
  t and language-neutral Web protocols.
• The Web services platform uses XSD as its type
  system. XML provides a simple way of representing
  data, but it says nothing about the standard set
  of data types available and how to extend that
  set. The data types you use must be translated to
  XSD types to conform to the Web services
  standards.
• Web services are not exclusive to .NET.
• NET includes several tools and a degree of
  support which simplify development of Web
  Services by automating many tasks involved and
  shielding the developer form many of the
  technical details.

3
More About Web Services

• Your Web service will sit behind a Web server,
  typically Internet Information Server (IIS).
• Support loosely coupled connections between
  systems.
• Works through existing proxies and firewalls.
• Can take advantage of HTTP authentication.
• Encryption for free with SSL.
• Web services only receive and return XML.
• Provide a stateless model similar to the
  singlecall activation mode. When a client invokes
  a remote method,the Server automatically
  constructs the relevant object, executes the
  method, returns any results, and discards the
  object. It is possible however, to maintain
  between method calls using the ASP.NET session
  object.

4
How are web services different from earlier
models of distributed computing, such as Corbra?

• Key differences
• loosely specified and coupled
• build on top of existing, ubiquitous
  infrastructure like HTTP and XML.

5
How are Web Services Described?

• Web Services are described using WSDL (Web
  Services Description language). These
  descriptions may be stored with the service
  itself or published in a UDDI registry.
• WSDL is an XML-based grammar for describing Web
  services, their functions, parameters, and return
  values.
• .NETs web service infrastructure will
  automatically generate the necessary WSDL to
  fully describe a .NET web service.
• .NET also provides tools that can consume WSDL
  descriptions of services and use these
  descriptions to generate proxy classes for use in
  client applications. So developers using .NET can
  remain ignorant of WSDL (and even SOAP) and
  create Web Services.

6
Example of a Service Description
xmlnss0"http//tempuri.org/"
name"TerraService" targetNamespace"http//
tempuri.org/" xmlns"urnschemas-xmlsoap-org
sdl.2000-01-25" mlsoap-orgget-sdl-2000-01-25"
href"http//207.46.235.37/terranet/terra
service.asmx/GetPlaceList"

name"imagePresence"/
ref"s0ArrayOfPlaceFacts"/


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How to Create a Web Service
To build a .NET Web service you create a file
with the .asmx extension.
8
Viewing a Test Page for the Web Service

• The framework provides built-in support for
  viewing and
• accessing methods exposed by a Web service. By
  accessing the
• Web service .asmx file, the framework
  automatically displays
• the public methods, as shown in figure below.

9
Testing the Web Service Continued

• The service method help page shows the XML
  representation of the request and response for
  the Web service, its arguments, and return types.
  You can also use the displayed HTML form to test
  the method.

10
How are Web Services Invoked?

• Soap (Simple Object Access Protocol) is the
  communications protocol for Xml Web Services.
• The Soap specification provides standards for the
  format of a SOAP message and how SOAP should be
  used over HTTP, which it uses as the transport
  layer to move structured type information across
  the Internet.
• SOAP also builds on XML and XSD to provide
  standard rules for encoding data as XML.
• Invoking a Web service from either a Web or
  desktop application is a simple matter of object
  instantiation and invocation. But which Object?
  This is where the proxy class comes into play.

11
Example of a SOAP Request
12
Proxy Classes

• The Proxy class is responsible for the following
• Generate SOAP request
• Send to the target service
• Receive the SOAP response
• Parse the SOAP Generate an object
• Return the object as a result
• The developer tools provided with the .NET SDK
  and Visual Studio .NET remove the need for the
  developer to work at the SOAP level. Instead,
  clients may calls against a proxy object derived
  from System.Web.Services.Protocols.SoapHttpClientP
  rotocol and .NET takes care of setting up,
  formatting and transmitting messages.
• The proxy class can be generated automatically
  using the command-line utility wsdl.exe.
• Contains not only the default constructor, but
  also methods to invoke the web service both
  synchronously and asynchronously.

13
Example of a Proxy Class
14
Example for invoking a temperature Web service
from an ASP.NET Web page
15
What is UDDI?

• Result of the combined efforts of several
  technology companies (chiefly IBM and Microsoft)
  to produce a global Internet-based registry of
  businesses and the web services they provide.
• UDDI represents a set of protocols and a public
  directory for the registration and real-time
  lookup of web services and other business
  processes.
• Yellow pages of Web Services

16
UDDI continued

• Consists of 2 parts
• First, UDDI is a technical specification for
  building a distributed directory of businesses
  and Web services. Data is stored within a
  specific XML format, and the UDDI specification
  includes API details for searching existing data
  and publishing new data.
• Second, the UDDI Business Registry is a fully
  operational implementation of the UDDI
  specification. The UDDI registry enables anyone
  to search existing UDDI data, for example, for
  providers of service in a specified geographic
  location or for businesses of a specified type.
  It also enables any company to register
  themselves and their services.

17
UDDI continued

• The data captured within UDDI is divided into
  three main
• categories
• White Pages This includes general information
  about a specific company. For example, business
  name, business description, and address.
• Yellow Pages This includes general
  classification data for either the company or the
  service offered. For example, this data may
  include industry, product, or geographic codes
  based on standard taxonomies.
• Green Pages This includes technical information
  about a Web service. Generally, this includes a
  pointer to an external specification, and an
  address for invoking the Web service.

18
When to Use Web Services?

• Web Services offer the most benefit in cases
  where
• applications need to communicate across platform
  boundaries
• and over the Internet
• Business to Business Integration
• Integrating business processes across multiple
  businesses is
• commonly referred to as business-to-business
  integration. By
• using Web services, a business can expose vital
  business
• processes to authorized suppliers and customers.
• Example You can expose electronic ordering and
  invoicing
• thereby enabling your customers to electronically
  send you
• purchase orders and your suppliers to
  electronically send you
• invoices.

19

• Application Integration
• A good portion of development efforts is spent
  integrating
• applications written in various languages and
  running on
• different systems.
•  
• Example You need to get data into your
  application from a
• legacy application running on an IBM mainframe or
  you need to
• send data from your application to a mainframe or
  Unix-based
• application somewhere. Even on the same platform,
  applications
• from different vendors often need to be
  integrated. By
• exposing some of its functionality and data via a
  Web service,
• an application provides a standard mechanism for
  other
• applications to integrate with it.
• Communicating through a firewall

20

• Software Reuse
• Software reuse has always been limited by one key
  factor you
• can reuse the code but not the data behind the
  code. The
• reason for this is you cannot easily distribute
  data unless it is
• fairly static data not expected to change much.
  Web services
• let you reuse code along with the data it needs.
• Example If your applications user enters a
  mailing address that you
• want to validate, you could send it to an address
  verification Web
• service. This service can lookup the street
  address, city, state and zip
• code to make sure the address exists and in the
  specified zipcode. A
• service like this is not possible with component
  reuse, you need to have
• the current database of street addresses, cities,
  states and zip codes.
• Another scenario for software reuse is when you
  are building
• an application that aggregates the functionality
  of several
• other applications you can use Web services to
  aggregate
• functionality from many applications into one,
  consistent, user
• interface.

21
When Not to Use Web Services
Situations where using Web Services will cost you
performance Single Machine Applications Applicat
ions that need to communicate with others running
on the same machine. In this case, it is almost
always better to use a native API rather than a
Web service because they require relatively
little overhead. Homogeneous Applications on a
LAN Homogenous applications running on the same
machine or on different machines that need to
communicate on the same LAN.
22
Web Service Review

• Service Side
• Write the service code
• Expects SOAP as input
• Define the externally visible methods
• Create the WSDL description of those methods
• Publish the WSDL
• Run the service
• Client Side
• Locate the WSDL
• Load the WSDL
• Convert to a client proxy
• Write the client code, calling proxy
• Generates and sends SOAP