Web Services

1
Web Services

• CS 6580

2
Web Services

• Internet-available services using XML messaging,
  for computer-computer interaction
  
• Not tied to any OS or language
• Self-describing public interface published, in
  XML
  
• Discoverable yellow pages to find services and
  interface descriptions

3
The Automated Web

• Standards mean lower barrier to application
  integration, possibly just-in-time

1. Discover services
Service Registry
2. Retrieve Service Description
3. Invoke remote service
Application
Web Server
Service Description
Web Service
4
Protocol Stack
Discovery UDDI
Description WSDL
XML messaging SOAP, XML-RPC, REST
Transport HTTP, SMTP, FTP, BEEP
5
XML-RPC

• Simple
• Request in XML, sent via HTTP POST
• Reply XML in HTTP response
• Sample request (minus HTTP headers)

6
XML-RPC response

• Response, minus HTTP headers

7
REST Representational State Transfer (aka
XML/HTTP)

• Simpler
• Request via HTTP GET, parameters in URL
• Result XML
• Ex) Visit http//www.amazon.com/webservices

GET /onca/xml?ServiceAWSECommerceServiceSubscrip
tionId15YAMHAMKKB9NK19SQ82OperationItemSearchS
earchIndexSportingGoodsKeywordsgolf20club20Ca
llaway (send above to webservices.amazon.com po
rt 80 using telnet)
8
SOAP Simple Object Access Protocol

• Complex
• Request and Reply in XML, over various protocols,
  usually HTTP
  

9
SOAP sample request
10
Service Description WSDL (Web Services
Description Language)

• An XML file containing
• Public functions
• Data types
• Binding info about protocol to use
• Address info for service
• (Extensions for SOAP)

11
Service Discovery UDDI (Universal Description,
Discovery, and Integration of Web Services)

• UDDI has 2 parts
• A technical spec for a distributed directory of
  businesses and web services
  
• Data stored in XML
• API for searching
• UDDI Business Registry an implementation of UDDI
  spec
  
• White pages general info (address, phone no.,
  etc)
  
• Yellow pages classification based on
  industry,product,etc
  
• Green pages tech info about a web service (SOAP,
  CORBA, Java RMI)