WSDL Web Services Description Language

WSDLWeb Services

Description Language

Presented By:

-Maitreya Natu

Outline

Introduction Document Structure Examining WSDL Web Services, Grids, Agents and WSDL References

What? Describes the technical details of how a Web Service works WSDL is a simple XML grammar for describing how to

communicate with a Web service It defines the messages (both abstract and concrete) that are

sent to and from a service It defines logical collections of messages (“port type”, “interface”) It defines how a given “port type” is bound to particular wire

protocols It defines where the service is located

Enables one to separate the description of abstract functionality offered by a service from concrete details.

Who?

WSDL 1.1 specification exists as a W3C Note, co-submitted by representatives of Microsoft and IBM

Why?

Classic IDL Model Almost all distributed systems have a language for describing

interfaces IDL in DCE and CORBA MIDL in COM and DCOM

Definitions are processed by an IDL compiler to generate stubs for clients which look like local function calls Dispatch routines for the server that invoke the developer’s

code WSDL acts as an IDL for Web Services distributed programming

model defines the communication protocol, the data transfer syntax and

location of the endpoint

How?

Developers use tool kits capable of reading and writing WSDL

Perl SOAP::Lite Constructs a local stub of a remote service object using WSDL

document as its template Programmer requests the local stub which silently

communicates with remote server SOAP::Lite -> service (

http://api.google.com/GoogleSearch.wsdl) -> do GoogleSearch(@parameters);

Microsoft’s .Net Web Services provides tools for consuming and producing WSDL documents wsdl.exe, creates a proxy class from a WSDL description

When?

WSDL 1.1, published as a W3C Note in March 2001

WSDL 1.2, published as W3C Working Draft in June 2003

Opinion

Principal advantage Wide acceptance as a fundamental component of

Web services Principal Disadvantage

Separates documentation from service Additional work to discover technical

specifications Stale WSDL files!

SOAP and WSDL

SOAP is a standard for communicating pure content. It needs a language to describe the content

SOAP messages carry type information It needs information about the service name, number of

parameters and types

WSDL automates the generation of client stubs for web services in a truly language and platform independent way

Document Structure

Abstract Section

Concrete Section

•Defines SOAP messages in a platform and language independent manner•Helps define set of services that several websites can implement

Site specific matters like serialization, bindings etc.

Document Structure

Types

Messages

Operations

Port Type

Bindings

Port

Service

Machine and language independent type definitions

Abstract typed definition of data communicated (function parameters)

Abstract description of supported action

Abstract set of operations supported

Document Structure

Types

Messages

Operations

Port Type

Bindings

Port

Service

A concrete protocol and data formatSpecification of a port type

A single endpoint defined as a combination of binding and networkaddress

A collection of related endpoints

Document Structure

<definitions><types>

Definition of types… …</types><message>

Definition of a message… …</message><portType>

<operation> <input message/> <output message/> </operation></portType><binding portType=“…”>

<operation> <input message/> <output message/> </operation></binding><service>

<port binding= “...”> Network Address… … </port></service>

</definitions>

Definitions







</definitions>

• Declares that document is XML• Defines the root element in the WSDL document <definitions>• Namespace declarations

Definitions

<?xml version=“1.0”?><definitions name=“StockQuote”

targetNameSpace=“http://example.com/stockquote.wsdl”xmlns:tns=“http://example.com/stockquote.wsdl”xmlns:xsdl=“http://example.com/stockquote.xsd”xmlns:soap=“http://scemas.xmlsoap.org/wsdl/soap/”xmlns=“http://schemas.xmlsoap.org/wsdl/”>

:::::

</definitions>• Declares that document is XML • Defines the root element in the WSDL document <definitions>• Namespace declarations

What are Namespaces for?

To avoid naming conflicts 2 services can use the same name only if they mean exactly

the same thing in both instances With 2 distinct namespaces, one web service “add” can

mean a different thing than other web service “add” Namespace attribute declares a shorthand for each

namespace used in the document http://www.infotects.com/addService#add ~ carlos:add If carlos is declared as a shorthand for

http://www.infotects.com/addService Location pointed by URI does not have to be a real web

location, they are use to guarantee uniqueness A GUID can be used instead “335DB901-D44A-11D4-A96E-0080AD76435D” is a valid

namespace designator

Types







</definitions>

• Declares the application specific data types• XML Schema allows for definition of complex data types which are equivalent to C structs

Types

<types> <schema targetNameSpace=“http://example.com/stockquote.wsdl”

xmlns=“http://www.w3.or/2000/10/XMLSchema”><element name=“TradePriceRequest”> <complexType>

<all> <element name=“tickerSymbol”

type=“string”/><all>

<complexType><element><element name=“TradePrice”> <complexType>

<all> <element name=“price” type=“float”/><all>

<complexType><element>

<schema></types>

• Declares the application specific data types• XML Schema allows for definition of complex data types which are equivalent to C structs

Messages







</definitions>

• Abstract definition of the data being transmitted• Consists of logical parts, each of which is associated with a type definition within some type system

Messages

<message name=“GetLastTradePriceInput”> <part name=“body” element=“xsdl:TradePriceRequest”/><message>

<message name=“GetLastTradePriceOutput”> <part name=“body” element=“xsdl:TradePrice”/><message>

• Abstract definition of the data being transmitted• Consists of logical parts, each of which is associated with a type definition within some type system (here an XML schema defined in types section)

Messages

Message part

Type Definition

<definitions …> <types> <schema …>

<element name=“PO” type=“tns:POType”/> <complexType name=“POType”>

<element name=“id” type=“string”/> <element name=“name” type=“string”/> <element name=“items”> <complexType>

<all><element name=“item” type=“int”>

</all></complexType>

</element> </complexType>

</schema> </types>

<messages name=“PO”> <part name=“po” element=“tns:tns:PO”/>

</message><definitions>

Messages

Message part

Type Definition

<definitions …> <types> <schema …>

<element name=“PO” type=“tns:POType”/> <complexType name=“POType”>

<element name=“id” type=“string”/> <element name=“name” type=“string”/> <element name=“items”> <complexType>

<all><element name=“item” type=“int”>

</all></complexType>

</element> </complexType>

</schema> </types>

<messages name=“PurchaseOrder”> <part name=“pOrder” element=“tns:PO”/>

</message><definitions>

Port Type







</definitions>

• A set of abstract operations • Each operation declares the abstract messages involved

Port Type

<portType name=“StockQuotePortType”> <operation name=“GetLastTradePrice”>

<input message=“tns:GetLastTradePriceInput”/> <output message=“tns:GetLastTradePriceOutput”/>

</operation></portType>

• A set of abstract operations • Each operation declares

• The name of method• Parameters• Types of each parameter

Port Type

<types> <schema …> <element name=“TradePriceRequest”>… type=“string”…</element> <element name=“TradePrice”> … type=“float” …</element> </schema></types>

<message name=“GetLastTradePriceInput”> <part name=“body” element=“xsdl:TradePriceRequest”/><message>

<message name=“GetLastTradePriceOutput”> <part name=“body” element=“xsdl:TradePrice”/><message>

<portType name=“StockQuotePortType”> <operation name=“GetLastTradePrice”>

<input message=“tns:GetLastTradePriceInput”/> <output message=“tns:GetLastTradePriceOutput”/>


Types

Message

Operations &Port Type

float GetLastTradePrice (string TradePriceRequest)

Operations WSDL operations refer to 4 transmission primitives

that an endpoint can support One-way: The endpoint receives a message Request-response: The endpoint receives a message, and

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

receives a correlated message Notification: The endpoint sends a message

These primitives are abstractly defined; a given binding describes the concrete correlation information

Operations: one way operation

<portType …> <operation …>

<input name=“…” message=“…”/> </operation></portType>

Operations: Request-response operation


<input name=“…” message=“…”/> <output name=“…” message=“…”/> <fault name=“…” message=“…”/>


Operations: Solicit-response operation


<output name=“…” message=“…”/> <input name=“…” message=“…”/> <fault name=“…” message=“…”/>


Operations: Notification operation


<output name=“…” message=“…”/></operation>

</portType>

Bindings







</definitions>

• defines a concrete protocol and data format specification for a particular port type• specifies how each operation call and response is sent on the wire (protocol, serialization and encoding)

Bindings

<binding name=“StockQuoteSoapBinding” type=“tns:StockQuotePortType”> <stk:binding preferredEncoding=“UTF-8” /> <soap:binding style=“rpc” transport=“http://schemas.xmlsoap.org/soap/http/”> <operation name=“GetLastTradePrice”>

<soap:operation soapAction = “http://example.com/GetLastTradePrice”/>

<input> <soap:body use=“encoded”

namespace=“http://tempuri.org/message/” encodingStyle=“http://schemas.xmlsoap.org/soap/encoding/” />

</input> <output> <soap:body use=“encoded”


</output> </operation></binding>

Bindings








• name: referred by ‘Port’ element in ‘Services’ section

•type: refers to port Type

Bindings








• style: (rpc or document)• transport: specifies the underlying protocol (here HTTP SOAP)

• MSTK2 extension element, sepcifies preferred encoding as “UTF-8”

Bindings








• corresponds to elements in PortTypes section

Bindings








• SOAP specific URI: gets used in SOAP message in SOAP Action header verbatim• Used for HTTP binding to identify the intent of the message

Bindings








• Specifies what gets into the body of the resulting SOAP message

Bindings








• Specifies whether the data is “encoded” or “literal”

Bindings








• prevents name clashing• this URI is used verbatim in the resulting SOAP message

Bindings








• determines the encoding style if use=“encoded”• For SOAP encoding, this should have the URI value of “http://schemas.xmlsoap.org/soap/encoding/”

Ports & Services







</definitions>

• Port: defines an individual endpoint by specifying a single address for a binding• Service: groups a set of related ports together

Ports

<service name=“StockQuoteService”>> <documentation> My First service </documentation> <port name=“StockQuotePort” binding=“tns:StockQuoteBinding”>

<soap:address location=“http://example.com/stockquote”/> </port></service>

• Ports: associates a location with a binding in a one to one fashion

Ports


<soap:address location=“http://example.com/stockquote”/> </port></service>

URL associated with the binding

Binding name as defined in Bindings section

Port Name (to differentiate among multiple ports)

Services


<soap:address location=“http://example.com/stockquote”/> </port></service> •None of the ports communicate with each other

•several ports can use same port type but employ different bindings or addresses

• There can be more than one service elements• Ports can be grouped in a service

• according to URL• according to protocol

Major Changes in WSDL V 1.2

Port Type is called Interface Interface Inheritance feature is added Better definition of HTTP 1.1 and SOAP 1.2

binding Describes how to use WSDL with SOAP,

HTTP and MIME

Examining WSDL

Verbosity WSDL First Too much flexibility adds overhead Get rid of difference between document and

RPC Binding style Get rid of difference between Literal and

Encoded Binding style Why 4 ways to define bindings?

Grids and WSDL

OGSA designed for both persistent and transient services together.

This will be achieved through Development of WSDL conventions Standard WSDL interfaces Behaviors of core services MatchMaker protocol to link services

Agents and WSDL

Agent ontology is defined using XML schema components

Behavior as a WSDL interface Performatives as operations with request response

messages Reference to external framework by Bindings

between abstract definition and implementation Agent Service logically as Endpoint with a physical

location and port

SOAP/WSDL vs ACLs

ASK, REPLY and TELL: 4 WSDL types of messages

ACL Content: Message Tags SENDER: defined in WSDL message as Service ERROR and SORRY: WSDL Fault Tag Ontology : XML Schema Agent Management Systems : SOAP for Transport Sophisticated message transport services: ??? Services requiring Negotiation: ???

Upcoming plans Web Services: Standardized enterprise components offered

across the Web Grid Services: scientific/ computing resources that facilitate

large-scale scientific research Multi-Agent systems: heterogeneous agents that cooperate or

compete to solve distributed AI problems Key research challenges are:

Support automated interoperability without human intervention Semantic Web Services: to make services accessible and

understandable Emerging ontologies (DAML-S): to construct semantically rich

service description

References W3C Note on WSDL 1.1 W3C Working Draft on WSDL 1.2 WSDL Explained

-Carlos C. Tapang Examining WSDL

-Rich Salz WSDL Gets a Close Look

-Darryl K. Taft All we Want for Christmas is a WSDL Working Group

-Martin Gudgin, Timothy Ewald Emerging Technology Briefs: WSDL

-Rael Dornfest, Clay Shirky WSDL First

-Will Provost Agents of the Grid: A Comparison with web Servies

-A. Avila-Rosas, UK International semantic Web conference, 2002, Italy

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WSDL Web Services Description Language

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