Describing Web Services An Overview of WSDL

Marco Cova – Describing Web Services: An Overview of WSDL – CS595G - 1/33

Describing Web Services An Overview of WSDL

CS595G: Web Services and Security1/17/2006

Marco Cova [email protected]


Outline

● Motivations● WSDL specification and an example● Tools● WSDL alternatives


Web Services Interaction

Typical steps in WS interaction:● Discovery: the requester entity becomes aware of the

provider entity either by directly knowing the provider agent's address or through some discovery service

● Agreement on service description: provider and requester agent “agree” on the service description

● Agents setup: web service description and semantics are input to requester and provider agents

● Messages are exchanged between the requester and provider agents


Web Services Stack

Image taken from http://www.oracle.com/technology/oramag/webcolumns/2003/techarticles/images/smith_wsc_f1.gif

Here, we will focus on the service description layer and WSDL specifically


Web Services description: goals and requirements

● To provide a structured, formal description of a web service:– What operations are available and how to

invoke them● To describe how to concretely access a web

service:– Web service address– Transport protocol

● What type of description: syntactical or semantic?


WSDL

● Web Service Definition Language: a language to describe web services

● XML-based

Status:● WSDL 1.1 is a W3C note published on 15 March

2001● WSDL 2.0 is a W3C Candidate Recommendation

(last update on 6 January 2006)


WSDL goals

● Service description: documentation for distributed systems– Language- and platform-independent

● Service automation: recipe for automating the details involved in the service invocation


WSDL: web service model

A WSDL document defines a web services as● Collection of communicating endpoints capable

of exchanging messages

For each web service, WSDL may provide two types of definitions:

● Abstract: the web service is seen as a language- and platform-independent interface

● Concrete: the web service is seen as a component accessible through specific transport and network standards


WSDL elementsMain WSDL elements:

● Types: container for data type definitions using some type system, typically XML Schema

● Message: an abstract, typed definition of the data being communicated

● Operation: an abstract description of an action supported by the service

● Port Type: an abstract set of operations supported by one or more endpoints

● Binding: a concrete protocol and data format specification for a particular port type

● Port: a single endpoint defined as a combination of a binding and a network address

● Service: a collection of related endpoints


WSDL elements – cnt'd

For each part of the specification, an example taken from the Amazon E-Commerce Service is presented. The full WSDL document is located at http://webservices.amazon.com/AWSECommerceService/AWSECommerceService.wsdl


wsdl:types

● Data type definitions needed to define the exchanged messages

● By default, the types are defined in terms of XML Schema

<definitions .... > <types> <-- type-system extensibility element --> * </types></definitions>


wsdl:types - example<types> ... <xs:element name="ItemSearch"> <xs:complexType><xs:sequence> <xs:element name="SubscriptionId" type="xs:string" minOccurs="0"/> <xs:element name="AWSAccessKeyId" type="xs:string" minOccurs="0"/> <xs:element name="AssociateTag" type="xs:string" minOccurs="0"/> <xs:element name="XMLEscaping" type="xs:string" minOccurs="0"/> <xs:element name="Validate" type="xs:string" minOccurs="0"/> <xs:element name="Shared" type="tns:ItemSearchRequest" minOccurs="0"/> <xs:element name="Request" type="tns:ItemSearchRequest" minOccurs="0" maxOccurs="unbounded"/> </xs:sequence> </xs:complexType></xs:element> ...</types>


wsdl:message

● Messages exchanged to provide a service● Messages are simply containers of parts which

are defined in terms of the types described in the types section

<definitions .... > <message name="nmtoken"> * <part name="nmtoken" element="qname"? type="qname"?/> * </message></definitions>


wsdl:message - example

<message name="ItemSearchRequestMsg"> <part name="body" element="tns:ItemSearch"/></message>

<message name="ItemSearchResponseMsg"> <part name="body" element="tns:ItemSearchResponse"/></message>


wsdl:portType

● A portType is a named set of abstract operations and the abstract messages involved

<wsdl:definitions .... > <wsdl:portType name="nmtoken"> <wsdl:operation name="nmtoken" .... /> * </wsdl:portType></wsdl:definitions>


Message exchange patterns

4 messaging types:● One-way: endpoint receives a message● Request-response: endpoint receives a message,

and sends a correlated message● Solicit-response: endpoint sends a message, and

receives a correlated message.● Notification: endpoint sends a message


wsdl:portType - example

<portType name="AWSECommerceServicePortType"> ... <operation name="ItemSearch"> <input message="tns:ItemSearchRequestMsg"/>

<output message="tns:ItemSearchResponseMsg"/> </operation> ...</portType>

In addition, a message can be used to communicate a fault: <fault message=”...”/>


wsdl:binding

● Message format and protocol details for operations and messages defined by a portType

<wsdl:definitions .... > <wsdl:binding name="nmtoken" type="qname"> * <-- extensibility element (1) --> * <wsdl:operation name="nmtoken"> * <-- extensibility element (2) --> * <wsdl:input name="nmtoken"? > ? <-- extensibility element (3) --> </wsdl:input> <wsdl:output name="nmtoken"? > ? <-- extensibility element (4) --> * </wsdl:output> <wsdl:fault name="nmtoken"> * <-- extensibility element (5) --> * </wsdl:fault> </wsdl:operation> </wsdl:binding></wsdl:definitions>


wsdl:binding – cnt'd

● Extensibility elements allow to specify– Concrete grammar for input, output and fault messages– Concrete per-binding information– Concrete per-operation information

● The WSDL specification introduces binding extensions for:– SOAP– HTTP GET/POST– MIME


wsdl:binding - example

<binding name="AWSECommerceServiceBinding" type="tns:AWSECommerceServicePortType">

<soap:binding style="document" transport="http://schemas.xmlsoap.org/soap/http"/> ...

<operation name="ItemSearch"> <soap:operation soapAction="http://soap.amazon.com"/> <input> <soap:body use="literal"/> </input> <output> <soap:body use="literal"/> </output> </operation>

...

</binding>


wsdl:port

● Defines an individual endpoint by specifying an address for a binding

<wsdl:definitions .... > <wsdl:service .... > * <wsdl:port name="nmtoken" binding="qname"> * <-- extensibility element (1) --> </wsdl:port> </wsdl:service></wsdl:definitions>


wsdl:port - example

<service name="AWSECommerceService"> <port name="AWSECommerceServicePort" binding="tns:AWSECommerceServiceBinding"> <soap:address location="http://soap.amazon.com/onca/soap?Service=AWSECommerceService"/> </port></service>


wsdl:service

● A service simply groups related ports together

<wsdl:definitions .... > <wsdl:service name="nmtoken"> * <wsdl:port .... />* </wsdl:service></wsdl:definitions>


Tools: editor

How do you write WSDL files?● By hand: some editors have special support for

WSDL● Don't write them: automatic generation (in a few

slides)


Tools: validation

● WSDL documents can be quite large (the Amazon E-Commerce Service WSDL document is 2432 lines of code and over 100KB)

● Tools to validate/analyze WSDL documents:– http://xmethods.net/ve2/Tools.po– http://www.softwaresecretweapons.com/jspwiki/

services/oy-lm-1.3/generator.jsp


Tools: WSDL generation and client generation

● Manually creating a WSDL file for a web service is a difficult and error-prone task

● Given a WSDL file, generating a client to interact with the service is a repetitive task

● There exist toolkits for all major languages that allow to automate both tasks


WSDL toolkit: Java

● Axis: http://ws.apache.org/axis/ – Builds stubs, skeleton and data types from WSDL

● java org.apache.axis.wsdl.WSDL2Java AWSECommerceService.wsdl

– Builds WSDL from Java code● java org.apache.axis.wsdl.Java2WSDL -o wp.wsdl

-l "http://localhost:8080/axis/services/WidgetPrice -n"urn:Example6" -p"samples.userguide.example6" "urn:Example6" samples.userguide.example6.WidgetPrice

● Axis2: http://ws.apache.org/axis2/


WSDL toolkit: Python

● SOAPpy: http://pywebsvcs.sourceforge.net/ ● Parsing a WSDL file:>>> from SOAPpy import WSDL>>> wsdlFile = 'http://webservices.amazon.com/AWSECommerceService/AWSECommerceService.wsdl'>>> server = WSDL.Proxy(wsdlFile)>>> server.methods.keys()[u'SellerListingSearch', u'CartCreate', u'SellerLookup', u'Help', u'TransactionLookup', u'CartAdd', u'ItemLookup', u'MultiOperation', u'SimilarityLookup', u'CartClear', u'ListLookup', u'CartModify', u'CustomerContentLookup', u'ListSearch', u'BrowseNodeLookup', u'CartGet', u'SellerListingLookup', u'CustomerContentSearch', u'ItemSearch']


WSDL toolkit: Python – cnt'd>>> itemSearchM = server.methods['ItemSearch']>>> for inparams in itemSearchM.inparams:... print inparams.name, inparams.type... body (u'http://webservices.amazon.com/AWSECommerceService/2005-10-05', u'ItemSearch')>>>>>> for outparams in itemSearchM.outparams:... print outparams.name, outparams.type... body (u'http://webservices.amazon.com/AWSECommerceService/2005-10-05', u'ItemSearchResponse')>>> result = server.ItemSearch({'body': {'SubscriptionId': 'xxxxxxxxxxxxxxxxxxxx', 'SearchIndex': 'Books', 'Request' : {'SearchIndex': 'Books', 'Title': 'restaurant end universe'}}})>>> result.Items.TotalPages2>>> result['Items'].TotalResults'18'


WSDL toolkit: Python – cnt'd

>>> result.Items.Item[0]<SOAPpy.Types.structType Item at -1214384084>: {'ItemAttributes': <SOAPpy.Types.structType ItemAttributes at -1214386100>: {'Title': 'The Restaurant at the End of the Universe', 'ProductGroup': 'Book', 'Author': 'Douglas Adams'}, 'ASIN': '0345391810', 'DetailPageURL': 'http://www.amazon.com/exec/obidos/redirect?tag=ws%26link_code=sp1%26camp=2025%26creative=165953%26path=http://www.amazon.com/gp/redirect.html%253fASIN=0345391810%2526tag=ws%2526lcode=sp1%2526cID=2025%2526ccmID=165953%2526location=/o/ASIN/0345391810%25253FSubscriptionId=xxxxxxxxxxxxxxxxxxxx'}


Lessons learned

● Working with complex types is... complex and not very interoperable

● Editing WSDL files by hand is masochistic. Avoid it as much as you can

● If everything seems fine but nothing works, double check your namespaces


Alternatives

● At the moment, WSDL 1.1 is “the” web service description language

● WSDL 2.0 redefines and cleans up the grammar specified by WSDL

● Simplify the XSD, SOAP/REST, WSDL stack: SSDL (SOAP Service Description Language), RESEDEL (REstful SErvices DEscription Language), WRDL (Web Resource Description Language), WADL (Web Application Description Language), SMEX-D (Simple Message EXchange Descriptor), WDL (Web Description Language)

● Add semantics description of a service: WSDL-S, WSML (Web Service Modeling Language)


End

● Questions?

Date post:	19-Jan-2016
Category:	Documents
Upload:	lynna
View:	23 times
Download:	0 times

Describing Web Services An Overview of WSDL

Documents