grid computing, b. wilkinson, 20043b.1 web services part ii

Grid Computing, B. Wilkinson, 2004 3b.1

Web ServicesPart II

Grid Computing, B. Wilkinson, 2004 3b.2

Web Services

From http://www.globus.org

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Address of a Web Service

• URIs

Example (URL)

http://www.cs.wcu.edu/webservices/math1

This does not exist, and if did, would only be meaningful to software.

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Client-Service Implementation

• Suppose we have found the service and have its WSDL description, i.e. got past step 4.

• In the implementation, it is convenient to use stubs - java classes suitable for web services defined with WSDL.

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Client Stub

• Between the client code and the network is a client stub, sometimes called client proxy.

• The client stub is responsible for taking a request from the client and converting the request into a SOAP request on the network - marshalling.

• Also responsible for receiving SOAP responses

on network and converting to a suitable form for client.

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Server Stub

• Between the service and the network is a server stub, sometimes called a skeleton.

• Responsible for receiving a SOAP request from the client stub and converting it into a suitable form for the service -unmarshalling.

• Also converts the response from the service into a SOAP message for the client stub.

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Web Service Application

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Steps

• Client calls client stub.

• SOAP request sent across network

• Server stub receives request and sends request to service

• Service send result to serve stub

• Server stub sends result across network to client stub.

• Client stub sends result to client.

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Web Service Application

Call client stubSOAP

requestRequest service

Result returnedSOAP

responseClient receives result

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Web Service Description

• Need a way of formally describing a service, what is does, how it is accessed, etc.

• An Interface Description language (IDL)

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Web Service Definition Language (WSDL)

A W3C standard XML document that describes three fundamental properties of a service:

• What it is - operations (methods) it provides.• How it is accessed - data format, protocols.• Where it is located - protocol specific network

address.

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Elements of a WSDL document

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Parts of a WSDL Document

Parts of an WSDL document::• Root definitions - namespaces

• portType definitions - abstract definition of service

• Message definitions - parameters in method signature

• Type definitions - data types

• Binding definitions - to protocols I.e. SOAP over HTTP

• Service definitions - where service is, ports

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portType

Describes “What” - an abstract definition of service operation. Uses the elements:

• message definitions - a set of parameters referred to by method signature, decomposed into parts

• type definitions - defines all data types used

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Binding

Describes “how” the elements in abstract interface (portType) are converted in actual data representations and protocols e.g. SOAP over HTTP.

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port and service

• Describes “where” service is.

• port - describes how a binding is deployed at the endpoint of a network

• service - a named collection of ports

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Root definitions

<?xml version=“1.0”?>

<definitions name=“PriceCheck”

targetNamespace=“http://www.skatestown.com/services/PriceCheck”

xmlns:pc=“http://www.skatestown.com/services/PriceCheck”

xmlns:avail=“http://www.skatestown.com/ns/availability”

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

xmlns:soap=“http://schemas.xmlsoap.org/wsdl/”>

.

<!-- other definitions -->

.

</definitions>

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portType definitions

<!-- Port type definitions -->

<portType name=“PriceCheckPortType”>

<operation name=“checkPrice”>

<input message=“PriceCheckRequest”/>

<output message=“PriceCheckResponse”/>

</operation>

</portType>

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Message definitions

<!-- Message definitions -->

<message name=“PriceCheckRequest”>

<part name=“sku” type=“xsd:string”/>

</message>

<message name=“PriceCheckResponse”>

<part name=“result” type=“avail:availabilityType”/>

</message>

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Type definitions

<!-- Type definitions -->

<types>

<xsd:schema targetNamespace=“http://www.skatestown.com/ns/availability”

xmlns:xsd=“http://www.w3.org/23001/XMLSchema”>

<xmlns:complexType name=“availabilityType”>

<xsd:sequence>

<xsd:element name=”sku” type=“xsd:string”/>

<xsd:element name=“price” type=“xsd:double”/>

<xsd:element name=“quantityAvailable” type=“xsd:integer”/>

</xsd:sequence>

</xmlns:complexType>

</xsd:schema>

</types>

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Binding definitions

<!-- Binding definitions -->

<binding name=“PriceCheckSOAPBinding” type=“pc:PriceCheckPortType”>

<soap:binding style=“rpc”

transport=“http://schemas.xmlsoap.org/soap/http”/>

<operation name=“checkPrice”>

<soap:operation soapAction=“”/>

<input>

<soap:body use=“encoded”

namespace=“http://www.skatestown.com/services/PriceCheck”

encodingStype=“http://schemas/xmlas.xmlsoap.org/soap/encoding?”/>

</input>

<output>

<soap:body use=“encoded”

namespace=“http://www.skatestpwn.com/services/PriceCheck”

encodingStype=“http://schemas/xmlas.xmlsoap.org/soap/encoding?”/>

</output>

</operation>

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Service definitions

<!-- Service definitions -->

<service name=“PriceCheckService”>

<port name=“PriceCheck” binding=“pc:PriceCheckSOAPBinding”>

<soap:address

location=

“http://localhost:8-8-/axis/services/PriceCheck”/>

</port>

</service>

</definitions>

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Building a ServicePreliminary to Assignment 1

To build (deploy) a service one has to create:

• a WSDL document for the service• the client stub• the server stub

and test with a client.

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Java Web Service (JWS)(The easy way to deploy a service)

• With JWS facility, service code with jws extension in the Axis-enabled web application is interpreted a web service.

• .jws file automatically compiled if necessary when service called.

• Simple and used in assignment 1 but has limitations.

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• Could actually use the web service after deployment with JWS without using a WSDL file nor stubs!

• Just use the service URL which would have a .jws extension - need some code in client and service to make SOAP calls.

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WSDL from Code

• One can write the service code (as a class or interface) and then use tools to generate the WSDL document.

– Axis Java2WSDL program generates WSDL file (and its scheme).

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WSDL from Running Service

• Another Axis tool can generate the WSDL document.directly from a running deployed service.

• add ?wsdl onto service URL.

• Example of this in assignment 1

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Stubs from WSDL

• If we have the WSDL document for the service, can use tools to generate client and server stubs:

– Axis WSDL2Java program generates stubs for use on client and server

– Example of this in assignment 1.