Web Services

1
Web Services

• What is web services
• How to program web services in ASP.NET
• What e-commerce business models do web services
  enable

2
Current Web Usage

• User-oriented browsing and data publication
• Users browse for information
• Vast databases are accessed through HTML gateways
  and user-friendly displays
• Example Yahoo stock ticker
• Yahoo has tons of stock price history behind
  http//quote.yahoo.com
• That information is easily accessible to anyone
  browsing the page
• But it is not easily extracted to be used by a
  program

3
XML and E-Commerce

• In the real-world, computers and database systems
  contain data in different formats.
• For developers one of the time-consuming most
  challenging tasks is to exchange data between
  systems over the Internet
• XML can used to store data and share data, thanks
  to its plain text format (easy to share) and
  flexibility.

4
What is Web Services

• Software components (application logic)
  accessible via standard Web protocols
• Loosely coupled, reusable software components
  that semantically encapsulate discrete
  functionality and are distributed and
  programmatically accessible over standard
  Internet protocols (Stencil Group)

5
What is Web Services (Contd)

• Web site with no user interface, but program
  interface programming the web
• Available to any client that speaks the right
  language--Web protocols (XML, SOAP, WSDL)
• Platform independent components
• Application Programming Interface (API) machine
  to machine

6
Web Services in ASP.NET

• Filename .asmx
• Greetings.asmx
• lt_at_ WebServicegt tag
• Namespace imports system.web.services
• Class definition
• The ltWebMethod()gt tag making it available to
  outside world (like API)
• Communicating between client and server through
  WS
• HTTP request and response
• SOAP wrapper sent as part of request/response

7
The Program

• Greetings.asmx
• Running on localhost, the web server on local
  machine
• Hello( ) is a public method of the Greetings class

8
Sending Data Using HTTP GET

• When the data is sent via HTTP GET,
  Request.QueryString can be used to access the
  name-value pairs
• Syntax of GETGET /class/590f04/code/greeting.asm
  x/Hello?NameYao HTTP/1.1Host localhost

9
Sending Data via HTTP POST

• Post /class/295s04/code/greetings.asmx/Hello
  HTTP/1.1
• Host localhost
• Content-Type application/x-www-form-urlencoded
• Content-Length 15
• NameYao
• (The last line of the example in the book, on
  Page 673, should be deleted)

10
Sending Information via SOAP

• Simple Object Access Protocol
• Wraps up information inside an XML element,
  called a SOAP envelope, and send it via HTTP
• See example on Page 612
• SOAP is the default Web Services protocol to send
  information in ASP.NET

11
Building Web Services in ASP.NET

• Four essential parts of WS
• Processing directive lt_at_ WebService
  Languagevb Classgreetingsgt
• Name spacesimports System.Web.Services
• Public classPublic class Greetings
• Web methodsltWebMethod()gt Public Function
  Name(Input as DataType) as Datatype

12
Creating a Web Service with Multiple Web Methods

• The Measurement Conversion Example
• Multiple web methods in one web service class
• WSDL the Web Service Description Language
• Describes the input and output parameters of a
  web service
• Itself an XML file

13
Why Are Web Services Interesting?

• For developers
• Access to a Web-wide library of software
  components
• Smart development tools can
• Help you locate useful Web Services
• Download service descriptions (WSDL)
• Automatically generate code from the WSDL to talk
  to the service using SOAP over HTTP
• On the server side, automatically generate WSDL
  for a service from its source code

14
Advantages For Businesses

• Better information availability Any-to-Any
  integration
• Integral assumption of development
• Must tie together islands of data, devices, OS,
  businesses, people
• New revenue opportunities
• Intelligent consumer devices
• New services
• Better customer service
• Open, internet based standards
• Broad accessibility

15
Benefits of Web Services

• Reduction of integration cost
• Currently 7 for ever 1 of software purchase
• Connect with and reuse existing assets
• Increase revenue opportunities
• Extend to new end-points and devices
• Broaden partnerships
• Expose functionalities within a program
• Enabling value chain integration
• Collaboration among several firms
• More use for customer and business information
  shared across firms