1 G52IWS: Web Services Description Language (WSDL) Chris Greenhalgh 2007-10-26.

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G52IWS: Web Services Description Language (WSDL)

Chris Greenhalgh2007-10-26

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Contents

• Standards• WSDL and web services• Anatomy of a WSDL definition document• WSDL bindings• WSDL tools

See also: “Developing Java Web Services”, ch 5 part (pp 201-222);WSDL 2.0 specification(s)

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Standards• First released 2000

– Microsoft, IBM, Ariba– Based on prior Network Accessible Services Specification

Language & SOAP Contract Language• March 2001 – WSDL 1.1 http://www.w3.org/TR/wsdl

– submitted to W3C as a Note• July 2002 – WSDL 1.2 draft

– Superceeded by WSDL 2.0 before fully standardised• June 2007 – WSDL 2.0 http://www.w3.org/2002/ws/desc/

– W3C Recommendation (standard)– Significantly redesigned – not directly compatible, but cleaner

and more general• See also: JSR 110: Java API for WSDL

http://www.w3.org/TR/wsdl

http://www.w3.org/2002/ws/desc/

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WSDL and web services

• Describes web service interface & semantics – how to invoke or call a web service

• Contains:– Interface information – publicly available functions– Data type information for incoming & outgoing

messages– Binding information about the protocol to be used– Address information for locating the web service

• Described services can be implemented in any language & on any platform

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WSDL and SOAP

• In principal a WSDL-described web service can be communicated with using any agreed protocol/transport, e.g.– SOAP– SMTP/MIME– HTTP (without SOAP)– MOM– …

• But it will often be SOAP– Or HTTP in simple cases

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Usage• May be generated from (describe) a Web service

– E.g. as in SampleServer2.jws– Or by hand

• May be used to specify and build a web service– E.g. as in SampleWebService.wsdl

• Link to WSDL published in a web services registry• Found by potential users

– “user” = application or programmer • Information is used to correctly communicate with the

web service– E.g. through creation and use of client-side stub classes– (Or construct an alternative but compatible service)

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Web-service lifecycle

“Developing Java Web Services” figure 5.1

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Anatomy of a WSDL 1.1 definition document

• Key elements:– <definitions> - document root element, specifying

service name & namespace(s)– <types> - data types, usually XML Schema

• (see XML notes)– <message> - logical definition of a one-way message– <portType> - abstract definition of the supported

operations in terms of specific messages– <binding> - specific protocol and data format for

portType– <port> - an address for binding to the service– <service> - the whole service: a set of related

(supported) ports

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<wsdl:definitions> element

• targetNamespace attribute identifies an XML Schema namespace for the WSDL document

• Defines other namespaces– Including standard wsdl namespace

WSDL1.1, xmlns:wsdl="http://schemas.xmlsoap.org/wsdl/"

– WSDL2.0: <description> in namespace xmlns:wsdl="http://www.w3.org/ns/wsdl"

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<?xml version="1.0" encoding="UTF-8"?><wsdl:definitions targetNamespace="http://localhost:8080/SampleServer2.jws" xmlns:apachesoap="http://xml.apache.org/xml-soap" xmlns:impl="http://localhost:8080/SampleServer2.jws" xmlns:intf="http://localhost:8080/SampleServer2.jws" xmlns:soapenc="http://schemas.xmlsoap.org/soap/encoding/" xmlns:wsdl="http://schemas.xmlsoap.org/wsdl/" xmlns:wsdlsoap="http://schemas.xmlsoap.org/wsdl/soap/" xmlns:xsd="http://www.w3.org/2001/XMLSchema">

http://www.cs.nott.ac.uk/~cmg/G52IWS/sample_soap/SampleServer2.wsdl

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<wsdl:types> element

• Typically XML Schema type definitions• For use in the messages/operations

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<wsdl:types> <schema targetNamespace="http://localhost:8080/SampleServer2.jws" xmlns="http://www.w3.org/2001/XMLSchema"> <import namespace="http://schemas.xmlsoap.org/soap/encoding/"/> <complexType name="ArrayOf_xsd_string"> <complexContent> <restriction base="soapenc:Array"> <attribute ref="soapenc:arrayType" wsdl:arrayType="xsd:string[]"/> </restriction> </complexContent> </complexType> </schema> </wsdl:types>


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<wsdl:message> element• Note: merged into operation input/output

element(s) in WSDL 2.0• Abstract definitions of all messages understood

by or sent by the web service• Each comprises a list of parts• Each part has

– Name– Element qualified name

• or type qualified name – not WSDL 2.0• As specified in types section or imported schema• Typically XML Schema

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<wsdl:message name="handleArrayResponse"> <wsdl:part name="handleArrayReturn" type="impl:ArrayOf_xsd_string"/> </wsdl:message> <wsdl:message name="handleArrayRequest"> <wsdl:part name="sa" type="impl:ArrayOf_xsd_string"/> </wsdl:message> <wsdl:portType name="SampleServer2"> <wsdl:operation name="handleArray" parameterOrder="sa"> <wsdl:input message="impl:handleArrayRequest" name="handleArrayRequest"/> <wsdl:output message="impl:handleArrayResponse" name="handleArrayResponse"/> </wsdl:operation> </wsdl:portType>


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<wsdl:portType> element• <interface> element in WSDL 2.0• Contains a list of the <operation>s supported• Each may have

– An <input> – An <output>

• WSDL 1.1 – each identifies a defined message• WSDL 2.0 – each defines a message, e.g. as an

XML Schema-defined element or list of elements (parts)

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portType Extension• WSDL 1.1

– Different portTypes may contain essentially the same operations (same messages, etc.) but are not explicitly related

• WSDL 1.2– One portType may “extend” another, i.e. include all

of its operations, plus add others• WSDL 2.0

– Similarly, one interface may “extend” one or more others, i.e. include all of their operations, plus add others

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<wsdl:message name="handleArrayResponse"> <wsdl:part name="handleArrayReturn" type="impl:ArrayOf_xsd_string"/> </wsdl:message> <wsdl:message name="handleArrayRequest"> <wsdl:part name="sa" type="impl:ArrayOf_xsd_string"/> </wsdl:message> <wsdl:portType name="SampleServer2"> <wsdl:operation name="handleArray" parameterOrder="sa"> <wsdl:input message="impl:handleArrayRequest" name="handleArrayRequest"/> <wsdl:output message="impl:handleArrayResponse" name="handleArrayResponse"/> </wsdl:operation> </wsdl:portType>


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WSDL operation types• One-way – input message only• Notification – output message only• Request-response – input then output, plus optional fault

message(s) (failure responses, cf. Java exceptions)– <fault> element (WSDL 1.1)

• Solicit-response – output then input, plus optional fault message(s)

• WSDL 2.0:– Renamed consistently: in and/or out– Extended to consider

• Optional responses• “Robust” messages (have a fault response on failure)

– Distinguishes incoming & outgoing faults

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WSDL operation types

“Developing Java Web Services”, figure 5.2

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<binding> element

• Defines the message format & protocol details for operations and messages defined in a particular portType– (or WSDL 2.0 interface).

• Provides binding information for all operations, messages and faults in the portType

• See later note on WSDL bindings

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<wsdl:binding name="SampleServer2SoapBinding" type="impl:SampleServer2"> <wsdlsoap:binding style="rpc" transport="http://schemas.xmlsoap.org/soap/http"/> <wsdl:operation name="handleArray"> <wsdlsoap:operation soapAction=""/> <wsdl:input name="handleArrayRequest"> <wsdlsoap:body encodingStyle="http://schemas.xmlsoap.org/soap/encoding/" namespace="http://DefaultNamespace" use="encoded"/> </wsdl:input> <wsdl:output name="handleArrayResponse"> <wsdlsoap:body encodingStyle="http://schemas.xmlsoap.org/soap/encoding/" namespace="http://localhost:8080/SampleServer2.jws" use="encoded"/> </wsdl:output> </wsdl:operation> </wsdl:binding>


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<service> element

• Specifies the type and location of a particular service

• WSDL 1.1– List of <port>s, each a particular <binding> of a

particular <portType>– Each with an address (e.g. URL)

• WSDL 2.0– Implemented overall interface– With a list of <endpoint>s, each with a particular <binding> on a particular address

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<wsdl:service name="SampleServer2Service"> <wsdl:port binding="impl:SampleServer2SoapBinding" name="SampleServer2"> <wsdlsoap:address location="http://localhost:8080/SampleServer2.jws"/> </wsdl:port> </wsdl:service></wsdl:definitions>


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WSDL bindings• Associate protocol and data format information

with abstract entities such as message, operation & portType (WSDL2.0 interface)

• Extensible, – i.e. new bindings can be specified & identified without

changing the WSDL standard• WSDL 1.1 has standard bindings for

– SOAP – HTTP GET & POST– MIME (not strictly a complete protocol)

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Example WSDL 1.1 SOAP 1.1 binding (as in examples)

• Binding must:– Identify SOAP 1.1 protocol– Identify data encoding– Specify address for SOAP endpoint

• And may– Identify SOAP action HTTP header URI– Define SOAP Envelope header entries

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<soap:binding> element

• Identifies use of SOAP (and version)• Identifies default server style

– document – XML document exchange– rpc – remote procedure call with

arguments/return values• Identifies transport binding

– transport=...– In this case HTTP as per SOAP specification

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<soap:operation> element

• Allows per-operation specification of SOAP style (rpc or document)

• Allows SOAP action header to be specified for that wsdl:operation

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<soap:body> element• Specifies mapping/encoding of message part(s)

to SOAP body• Affected by operation style:

– rpc • Body contains an element named after the operation• Each part appears within the operation element as a named

wrapper element – literal

• Body contains parts directly• Affect by message specification

• If “type” then type applies to Body or wrapper itself• If “element” then that element is added as child

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Example document/literal bodyWSDL:<wsdl:message name="listMatchingResponse"> <wsdl:part name="body" element="types:nameValuePair" /></wsdl:message><wsdl:operation name="listMatching"> <wsdl:input message="service:listMatchingRequest" name="listMatchingRequest" /> …</wsdl:operation>

SOAP:<soapenv:Body> <nameValuePair xmlns="http://www.cs.nott.ac.uk/~cmg/G52IWS/SampleWebServiceTypes"> <name xmlns="">subject</name> <value xmlns="">Chris</value> </nameValuePair> </soapenv:Body>

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Example rpc/encoded bodyWSDL:<wsdl:message name="handleStringRequest"> <wsdl:part name="s" type="xsd:string" /> </wsdl:message><wsdl:operation name="handleString" parameterOrder="s"> <wsdl:input message="impl:handleStringRequest" name="handleStringRequest" /> … </wsdl:operation>

SOAP:<soapenv:Body> <ns1:handleString soapenv:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/" xmlns:ns1="http://DefaultNamespace"> <s xsi:type="xsd:string">abc</s> </ns1:handleString> </soapenv:Body>

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<soap:body> element attributes

– parts="(part name list)" – optional, parts to appear in SOAP body (specifically)

– use="literal" – part(s) (elements or types) are XML and appear directly

– use="encoded" – parts (types only) are abstract types and are encoded into XML

– encodingStyle="(encoding URI(s))" identifies encoding used, required for encoded

• Typically SOAP encoding– namespace="URI" – for encoded content not

explicitly defined by the abstract type(s)

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<soap:address> element

• Specifies service endpoint address– In this case an HTTP URL (HTTP transport)

<wsdl:service name="SampleServer2Service"> <wsdl:port binding="impl:SampleServer2SoapBinding" name="SampleServer2"> <wsdlsoap:address location="http://localhost:8080/SampleServer2.jws"/> </wsdl:port> </wsdl:service></wsdl:definitions>

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WSDL tools• Possible capabilities

– WSDL generation – from an existing service• E.g. as seen with SimpleServer2.jws• Also AXIS java2WSDL

– WSDL compilation – generate data structures and skeleton for service implementation

• E.g. as seen with SimpleWebService.wsdl server • using AXIS WSDL2Java

– WSDL proxy generation – produce client stub for a particular language encapsulating all details for invoking the web service

• E.g. as seen with SimpleWebService.wsdl & SimpleClient.java

• Also AXIS WSDL2Java• See examples (notes & code)

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Limitations of WSDL

• Unable to describe complex business processes– E.g. multiple web services, sequences of

related messages– See WS-CDL, BPEL, ebXML CCP/A, …

1 G52IWS: Web Services Description Language (WSDL) Chris Greenhalgh 2007-10-26.

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