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WSDL: Web Service Description Language – Overview and Structure

Learn about WSDL, a language used to describe and locate web services. Understand the elements of a WSDL document and how SOAP messages are mapped to WSDL. Explore the types, messages, ports, and operations defined in a WSDL document.

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WSDL: Web Service Description Language – Overview and Structure

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  1. T-110.5140 Network Application Frameworks and XML Web Services and WSDL15.04.2008Sasu Tarkoma Based on slides by Pekka Nikander

  2. What is WSDL? • WSDL: Web Service Description Language • An XML language used to describe and locate web services • location of web service • methods that are available • data type information and XML messages • Commonly used to describe SOAP-based services • W3C standard (work in progress) • Initial input: WSDL 1.1 as W3C Note • Current version 2.0 (Recommendation) • Some differences between 1.1 and 2.0 • WSDL 1.1 in WS-I Basic Profile 1.0 and 1.1.

  3. WSDL Document Elements (v.1.1.) • <types> - data type definitions • <message> - Abstract definition of the data being transmitted • <portType> - A set of abstract operations • <binding> - Concrete protocol and data format specifications for the operations and messages defined by a particular portType. Endpoint type. • <port> - An address for binding. Endpoint instance. • <service> - A set of ports.

  4. WSDL Overview <definitions>: ROOT WSDL element <types>: The data types that are used <message>: What messages are transmitted? <portType>: The supported operations <binding>: The binding to concrete protocols <service>: Reference to actual location

  5. A WSDL Document • A WSDL document contains two parts • Abstract part • Interfaces, types, messages • Concrete part • Binding to conrete protocol and encoding • May be published separately • Interfaces agreed between many companies • Each company published their own implementation in UDDI and import the abstract interface.

  6. Mapping SOAP to WSDL

  7. Message Styles • The WSDL 1.1 specification defines two SOAP message styles • Determined in binding • Document • <soap:Body> contains one or more child elements called parts • There are no SOAP formatting rules for what the <soap:Body> contains • preferred, loose coupling, easy validation • RPC • <soap:Body> contains an element with the name of the method or remote procedure being invoked • This element in turn contains an element for each parameter of the procedure • less popular today, tighter coupling

  8. The main structure (v.1.1) <definitions namespace = "http://.."> <types>XML Schema types</types> <message>..</message> <portType>a set of operations</portType> <binding>Communication protocols</binding> <service>A list of binding and ports</service> </definitions>

  9. Types • <types> define data types used in message declaration • For platform neutrality, WSDL uses XML Schema syntax to define data • XML Schema must be supported by any vendor of WSDL conformant products • Other kinds of type definitions also possible • Possible interoperability issues • If the service uses only XML Schema built-in simple types, such as strings and integers, the types element is not required

  10. WSDL Messages • The <message> element defines the data elements of an operation • the name of the message • contains zero or more message part elements • The parts can be compared to the parameters of a function call in a traditional programming language • All parts are typed by an XML Schema type • V.2.0 changes: message element is not used, replaced by patterns

  11. WSDL Ports • The <portType> element is the most important WSDL element • The operations that can be performed, the messages that are involved • A <port> defines the connection point to a web service, an instance of <portType> • It can be compared to a function library (or a module, or a class) in a programming language

  12. Operation Types (v.1.1) • One-Way: The operation can receive a message but will not return a response • Request-Response: The operation can receive a request and will return a response • Solicit-Response: The endpoint sends an output message and then receives an input message. • Notification: The operation can send a message but will not wait for a response • v.2.0 changes: abstract message patterns

  13. <message name="GetLastTradePriceInput"> <part name="body" element="TradePriceRequest"/> </message> <message name="GetLastTradePriceOutput"> <part name="body" element="TradePrice"/> </message> <message name=”ExampleInteraction"> <part name="index" type="xsd:integer"/> <part name="name" type="xsd:string" /> </message>

  14. Example <portType name="StockQuotePortType"> <operation name="GetLastTradePrice"> <input message="tns:GetLastTradePriceInput"/> <output message="tns:GetLastTradePriceOutput"/> </operation> </portType>

  15. One way and Notification Example <portType name="RegisterPort"> <operation name="register"> <input name="customerInfo" message="RegInfo"/> </operation> <operation name="registerResponse"> <output name="response" message="ResponseInfo"/> </operation> </portType>

  16. Putting it together Source: http://msdn.microsoft.com/

  17. WSDL 2.0 • 3 specifications • Part 1: Core • Abstract interfaces, independent of protocol and encoding • Part 2: Message Exchange Patterns • Predefined types of interactions • Part 3: Bindings • SOAP and HTTP/MIME binding • Lot’s of changes from 1.1

  18. Changes from 1.1 to 2.0 • Adding further semantics to the description language. • Removal of message constructs. These are specified using the XML schema type system in the types element. • No support for operator overloading. • PortTypes renamed to interfaces. Support for interface inheritance is achieved by using the extends attribute in the interface element. • Ports renamed to endpoints. • Abstracted message patterns

  19. WSDL 2.0 Conceptual Model Source: http://webservices.xml.com/pub/a/ws/2004/05/19/wsdl2.html

  20. Message Exchange Patterns MEP Description Fault in-only Single input message No robust-in-only Single input message Trigger In-out Input message + output message Replace out-only Single output message No robust-only-out Single output message Trigger out-in Output followed by input msg Replace out-optional-in Output followed by an opt. Input Trigger in-optional-out Input followed by an opt. Output Trigger

  21. Implementations • Microsoft .NET • SOAP 1.1, WSDL 1.1 • Java API for XML-based RPC (JAX-RPC) • SOAP 1.1, WSDL 1.1 • Java API for XML Registries (JAXR) • Apache Axis • Tools for automatically creating WSDL to/from Java • SOAP 1.1 and 1.2, WSDL 1.1, JAX-RPC 1.0 • Axis2 supports WSDL 2.0 component model • IBM Websphere, BEA Web Logic, SAP NetWeaver, …

  22. Uses of WSDL documents • Description of service interfaces • Compile-time • Developer uses WSDL before service deployment • Run-time • Client downloads WSDL description and uses the info it provides to execute the service • As a side-effect • Developers can use WSDL to speed up the development of code • WSDLJava code • Java interfaces  WSDL

  23. Summary • Deferred binding, using Web, composition • Some details and conventions still unclear • Possible interoperability issues • Parts hard to understand • Namespaces • Schemas • Differences between versions • Document vs. RPC SOAP style • Also literal vs. encoded • More about this next week

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