Web Services

1
Web Services

• Ellen Lay
• Software Developer
• March 26, 2008

2
What is a Web Service?
A Web Service is a software system designed to
support interoperable machine-to-machine
interaction over a network.
-World Wide Web Consortium (W3C)

• Clients and Servers that communicate over HTTP
  protocol that are used on the web.

3
What is a web service?
A web service is any service

• that is available over the internet
• Uses a standardized XML messaging system
• Not tied to any operating system
• Not tied to any programming language

Should also be

• Self describing // publish interface for use
• Discoverable // register service

4
Background
(How did web services come to exist?)

• Companies computerize their services resulted in
  isolated computer systems
• Mergers, acquisitions, business growth happened
• Internet helped out BUT
• Work around new distributed technologies
  emerged RMI, DCOM, CORBA clunky!

5
So what makes web services better?

• Based on existing, well known HTTP
• Uses XML messages
• Based on set of standardized rules and
  specifications (makes it portable)
• Developer friendly
• Lots of SOAP tools available in many programming
  languages
• Lots of XML tools that read, write, generate XML

6
What are the goals of web services?

• Sharing of information, and computing routines
  between remote, isolated computer systems made a
  lot cheaper and easier
• Makes Business-to-Business communication more
  efficient

7
Web Terminology

• URI Uniform Resource Identifier
• Internet
• The hardware and software infrastructure part of
  the global network of interconnected computers
• the Web
• Very large set of interlinked hypertext documents
  (webpages) accessed via the Internet
• Note
• the Web is not synonomous with the Internet

8
Hypertext Transfer Protocol (HTTP)

• Document-based protocol
• Client puts a document in an envelop, sends to
  server
• Server replies by putting a response in envelope
  and sends to client.
• Strict standards for how to address envelope
• Envelope contents can be anything

9
HTTP Request
The path
HTTP Method
Request Headers (metadata) 8 total
Document inside
10
The Human Centric Web

• Humans are actors
• user web browsers
• Audio players
• Other front end GUIs

Users Focused on retrieval display of
data Content raw data presentation mark up
11
Amazon book search example
12
Search results (human)
13
Web Services The Programmable Web

• Conversations take place between applications, as
  easily as between web browsers servers
• Based on XML, and HTTP
• Examples

• Package Tracking
• Credit Card Verification
• Language Translation Babel fish
• Shopping Bots

Content raw data // Meant as input to
applications Applications are interpreting
response instead of humans
14
Run Ruby Code, Get Output
Run the Ruby Code
Program/Client Output - XML Document
15
What XML is!

• Extensible Mark up Language (XML)
• Simple, Flexible, Strict, Portable,
  Standards-based Format
• Defines a generic syntax used to mark up data
  thats
• Simple
• Human Readable
• Delivers valid data!

• XML Specification has strict rules, (grammar)
  about document format
• Allowed placement of tags
• How attributes can be attached to elements
• Where tags can appear
• Acceptable names for tags
• Which elements are legal

16
How does XML differ from HTML?

• XML is a structural, semantic markup language.
  HTML is a presentation language
• XML you can create your own tags. HTML
  finite set of predetermined tags
• XML is flexible, you can define your own tags
  as you need them. HTML you cannot define your own
  tags.
• XML provides strict rules for structure of a
  document.
• XML application (i.e. SVG), is a set of defined
  XML tags

17
XML is Cool!

• XML simply the most robust, reliable, and
  flexible document syntax ever invented
• XML is syntax of choice for newly designed
  document formats across almost all computer
  applications
• Interesting examples
• Used to trade stocks on Wall Street
• Save state of video games
• Delivers real-time game scores to cell phones

18
XML Flexible? OMG

• Example XML Applications

• Flexible enough to be customized for domains as
  diverse as

• Websites
• Electronic data interchange
• Geneology
• Real estate listing
• Object serialization
• Remote Procedure Calls (RPCs)
• Voice mail systems

• SAX
• SVG
• MathML
• CML
• KML

19
Steps in Creating Web Services

• Step 1 Define the data that comprises a request
  - URL, arguments, XML/HTML/JSON
• Step 2 Create HTTP request
• Step 3 Parse/interpret the response data
  stickers say how to parse/interpret
• Two Approaches
• Current Standard Big Web Services/SOAP
  Services
• Emerging Standard RESTful Services

20
How do Big Web Services work?