10. Web Services Description Language

July 09, 2002, http://www.w3.org/TR/wsdl12/ - The World Wide Web Consortium (W3C) announced the publication of initial working draft specifications for Web Services Description Language (WSDL) Version 1.2 and Web Services Description Language (WSDL) Version 1.2: Bindings. In the introduction section of this document, it explain what is WSDL: “… WSDL describes Web services starting with the messages that are exchanged between the service provider and requestor. The messages themselves are described abstractly and then bound to a concrete network protocol and message format. A message consists of a collection of typed data items. An exchange of messages between the service provider and requestor are described as an operation. A collection of operations is called a portType. Collections of portTypes are grouped and called a serviceType. A service represents an implementation of a serviceType and contains a collection of ports, where each port is an implementation of a portType, which includes all the concrete details needed to interact with the service.”

What is WSDL?

XML language for describing web services as a set of endpoits (ports) of message exchange
Each endpoint consists of

Definitions of operations and messages
Binding protocol and message format

WSDL for describing a Web Service of a message exchange using XML-based contract

Consists of a collection of typed data items
Operation: exchanged between service provider and requestor
portType: a collection of operations
serviceType: a group of collections of portTypes
service: an implementation of serviceType and contains a collection of ports, where each port is an implementation of a portType, which include all the concrete details needed to interact with the service

WSDL Usage Scenarios, http://www.w3.org/TR/ws-desc-usecases

Messaging

UC0001 Fire–and-forget – update status example
UC0002 Oneway Message with Guaranteed Delivery [WS] – enterprise messaging (JMS example)
UC0006 Document Centric Computing [WS] – attach document along with other regular messages (ebXML Web service example)
UC0015 Request-Response [WS] – e-Business example
UC0025 Event notification [WS] – return output messages
UC0028 Sync/Async Operations [WS] – blocking/non-blocking messaging
UC0030 Events [WS] – push, poll (send a SOAP request)

Specifications

UC0003 Multiple Faults

UC0004 Service Level Attributes
UC0005 Operation Level Attributes
UC0029 Namespaces with data and interfaces
UC0031 Versioning
UC0032 Classification System for Operation
UC0033 Header Specification – additional routing header info
UC0034B Specifying streaming – A Webcam video streaming over HTTP
UC0035 Extending PortType – an example, Universal Plug and Play (UPNP) devices

Service References

UC0027 References

Meta Data

UC0026 Service Metadata

Miscellaneous

UC0034A Obtaining WSDL from the web service itself

WSDL Requirements, http://www.w3.org/TR/sw-desc-reqs/

Notations – keywords: MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD NOT, RECOMMENDED, MAY, OPTION
Definitions: Web Services, Message, Operation, InterfaceBinding, EndPoint, etc
Requirements:

General: R001,R004, R099, R100, etc
Simplicity: R013, R014
Interface Description: R021, R022, etc
Description of Interaction with a Service: R036, R044, etc
Messages and Types: R046, R085
Service Types: R118, R058
InterfaceBindings
Reusability
Extensibility
Versioning
Security
Mapping to Semantic Web

Requirements from other W3C WGs

Web Services Description Language (WSDL) Specification

WSDL Specification Version 1.1, http://www.w3.org/TR/2001/NOTE-wsdl-20010315
WSDL Specification Version 1.2, http://www.w3.org/TR/wsdl12, 9 July 2002
WSDL Specification 1.2: Binding, http://www.w3.org/TR/2001/NOTE-wsdl-20010315, 9 July 2002

WSDL Document Syntax Defines 6 kinds of Component

Root - WSDL Definition Element with five types of child elements

service description (Ports: Ending Port1, Ending Port2, etc)
binding description (Operations: SOAP_Protocol, SOAP_Protocol, etc)
serviceType description
portType description (Operations: Method Call_1, Method Call_2, etc)
message description (Part: Schema-Mess1, Schema-Mess2, etc)
type description (Types - Schema_simpleType, Schema - complexType)

WSDL Root and Child Elements

definitions – the root element

targetNamespace attribute - base URI required

types - element for enclosing data type definitions

When XSD is used as the type system, types element should contain the schema definition through http://www.w3.org/2001/XMLSchema
schema – element
simpleType
complexType

message – element

part - element

portType – element

operation – element

input – element
output – element

binding – element

operation – element
input – element
output – element

service - element

document – element
port - element

Example: A SubscribeToQuotes SOAP 1.1 one-way message, a StockQuote Service via SMTP Binding, cited from http://www.w3.org/TR/wsdl12-bindings/

Request Message: a ticker symbol of type string, and includes a header defining the subscription URI

Example: A GetTradePrice SOAP 1.1 RPC requests StockQuote Service via HTTP Binding, cited from http://www.w3.org/TR/wsdl12-bindings/

Request Message:

tickerSymbol: ticker symbol of type string, a time of type timeInstant

Return Message: the price as a float in the SOAP response

Example: A GetTradePrice SOAP 1.1 requests StockQuote Service via HTTP Binding, cited from http://www.w3.org/TR/wsdl12-bindings/

Request Message:

tickerSymbol: a stock quote symbol string, a
timePeriod: an application defined TimePeriod structure containing a start and end time

Return Message:

frequency:
an array of float: stock prices recorded by the service within that period of time, as well as the frequency at which they were recorded as the SOAP response

Example: A Web Services Example: Calculator with Multiply and Divide Methods

<?xml version="1.0" encoding="utf-8"?>

<definitions targetNamespace="http://domain_name/Calculator/wsdl"

xmlns:tns="http://domain_name/Calculator/wsdl"

xmlns:xsd="http://www.w3.org/2001/XMLSchema"

xmlns:s="http://domain_name/Calculator/schema"

xmlns="http://schemas.xmlsoap.org/wsdl/">

<types>

<schema attributeFormDefault="qualified"

elementFormDefault="qualified"

xmlns="http://www.w3.org/2001/XMLSchema"