Introduction to WSDL

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Introduction to WSDL

• presented by Xiang Fu

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Source

• WSDL 1.1 specification
• http//www.w3.org/TR/wsdl
• WSDL 1.2 working draft
• http//www.w3.org/TR/wsdl12/
• W3C School Tutorial
• http//www.w3schools.com/wsdl/wsdl_intro.asp

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What is WSDL

• Web Service Description Language.
• An XML language used to describe and locate web
  services.
• Written in XML.
• Describe functionality of a web service
• Specify how to access the service (binding
  protocol, message format, and etc.)
• Not a W3C standard yet.
• Version 1.1 released March 2001
• Working draft of Version 1.2 released July 2003

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Related Standards

• Type System XML Schema
• Name space XML namespaces
• Binding SOAP, HTTP, MIME and etc.

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The Main Structure of WSDL

• ltdefinition namespace http/ gt
• lttypegt xschema types lt/typegt
• ltmessagegt lt/messagegt
• ltportgt a set of operations lt/portgt
• ltbindinggt communication protocols lt/bindinggt
• ltservicegt a list of binding and ports lt/servicegt
• ltdefinitiongt

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Types

• lttypesgt define types used in message declaration
• XML Schema, DTD, and etc.
• XML Schema must be supported by any vendor of
  WSDL conformant products.

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• lttypesgt
• ltschema targetNamespace"http//example.com/sto
  ckquote.xsd" xmlns"http//www.w3.org/2000/10/XMLS
  chema"gt
• ltelement name"TradePriceRequest"gt
• ltcomplexTypegt
• ltallgt
• ltelement
  name"tickerSymbol" type"string
• minOccur 1
  maxOccur10/gt
• ltelement name paymentgt
• ltcomplexTypegt
  ltchoicegt
• ltelement name
  account typestringgt
• ltelement name
  creditcard typestringgt
• lt/choicegt
  lt/complexTypegt
• lt/elementgt
• lt/allgt
• lt/complexTypegt
• lt/elementgt
• lt/schemagt
• lt/typesgt

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WSDL Messages

• The ltmessagegt element defines the data elements
  of an operation.
• Each messages can consist of one or more parts.
  The parts can be compared to the parameters of a
  function call in a traditional programming
  language.

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ltmessage name"GetLastTradePriceInput"gt ltpart
name"body" element"TradePriceRequest"/gt
lt/messagegt ltmessage name"GetLastTradePriceOutp
ut"gt ltpart name"body" element"TradePrice"/gt
lt/messagegt
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WSDL Ports

• The ltportTypegt element is the most important WSDL
  element.
• It defines a web service, the operations that can
  be performed, and the messages that are involved.
• The ltportgt defines the connection point to a web
  service, an instance of ltportTypegt.
• It can be compared to a function library (or a
  module, or a class) in a traditional programming
  language. Each operation can be compared to a
  function in a traditional programming language.

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ltportType name"StockQuotePortType"gt
ltoperation name"GetLastTradePrice"gt
ltinput message"tnsGetLastTradePriceInput"/gt
ltoutput message"tnsGetLastTradePriceOutput"
/gt lt/operationgt lt/portTypegt
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Operation Types

• The request-response type is the most common
  operation type, but WSDL defines four types

• One-way The operation can receive a message but
  will not return a response
• Request-responseThe operation can receive a
  request and will return a response
• Solicit-responseThe operation can send a request
  and will wait for a response
• NotificationThe operation can send a message but
  will not wait for a response
• -- v 1.2 addition
• request multiple response

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One way and Notification Example
ltportType nameRegisterPort"gt ltoperation
nameregister"gt ltinput namecustomerInfo"
messageRegInfo"/gt lt/operationgt
ltoperation name register Responsegt
ltoutput name response messageResponseInfo/gt
lt/operationgt lt/portType gt
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Binding

• Binding defines how message are transmitted, and
  the location of the service.

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ltbinding name"StockQuoteSoapBinding"
type"tnsStockQuotePortType"gt
ltsoapbinding style"document"
transport"http//schemas.xmlsoap.org/soap/http"/gt
ltoperation name"GetLastTradePrice"gt
ltsoapoperation soapAction"http//example.co
m/GetLastTradePrice"/gt ltinputgt
ltsoapbody use"literal"/gt
lt/inputgt ltoutputgt
ltsoapbody use"literal"/gt lt/outputgt
lt/operationgt lt/bindinggt
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ltservice name"StockQuoteService"gt
ltdocumentationgtMy first servicelt/documentationgt
ltport name"StockQuotePort" binding"tnsStockQuo
teBinding"gt ltsoapaddress
location"http//example.com/stockquote"/gt
lt/portgt lt/servicegt
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WSDL and UDDI

• Description of web service.
• Discovery of web service?
• UDDI yellow page.

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What is UDDI

• UDDI is a platform-independent framework for
  describing services, discovering businesses, and
  integrating business services by using the
  Internet.
• UDDI stands for Universal Description, Discovery
  and Integration
• UDDI is a directory for storing information about
  web services
• UDDI is a directory of web service interfaces
  described by WSDL

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How can UDDI be Used

• If the industry published an UDDI standard for
  flight rate checking and reservation, airlines
  could register their services into an UDDI
  directory.
• Travel agencies could then search the UDDI
  directory to find the airline's reservation
  interface.
• When the interface is found, the travel agency
  can communicate with the service immediately
  because it uses a well-defined reservation
  interface. (by WSDL)

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Whats missing?

• Quality of service. (how fast, how reliable?)
• Smart Searching (currently business code match)
• DAML-S project.
• DARPA Agent Markup Language for web Services.
• Describes control flow
• Quality of service.
• Support smart discovery of service
• Ontology based technology.
• A big dictionary defining the relations between
  concepts.
• e.g. vehicle car truck

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Problems

• Complex long running web services.
• Communication infrastructure
• Asynchronous communication
• Analysis and verification
• Automatic composition of complex services.