Web Services tying it all together and Introduction to Grid Services Concepts

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Web Services(tying it all together)and
Introduction to Grid Services Concepts

• These slides are adapted from course material
  developed by Barry Wilkinson, http//sol.cs.wcu.ed
  u/abw/CS493F04/

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Web Services

• Software components designed to provide specific
  operations (services) accessible using standard
  Internet technology.
• Similar to RMI, CORBA,
• Client/server
• Platform independent
• Usually through SOAP (simple Object Access
  Protocol) messages carrying XML documents, and a
  HTTP transport protocol.

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Service-Oriented Architecture

• Steps
• Services published in a Service registry.
• Service requestor asks Service Registry to locate
  service.
• Service requestor binds with service provider
  to invoke service.

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Service-Oriented Architecture
Service registry
1. Publish
2. Find
3. Bind
Service requester
Service provider
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Web Services Stack
XML
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Calling a Web Service
From http//www.globus.org
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Address of a Web Service

• Uses URIs (Uniform Resource Identifiers) - web
  naming mechanism.
• URLs are a subset of URI, and would typically be
  used, e.g.
• http//talon.csce.uark.edu/aapon/myMath

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• URIs also include email addresses, i.e.
• mailtoaapon_at_uark.edu
• and
• Uniform Resource Names (URNs) which are globally
  unique and persistent. UDDI uses URNs.

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Hosting Environments for Web Services

• Microsoft .NET
• IBM Websphere
• Apache Axis - we are using this for the Web
  Services exercise

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Client-Service Implementation

• Just as in Java RMI, client and server stubs are
  used to handle the networking details.
• Java classes suitable for web services defined
  with WSDL.
• Client stub marshalls the request,
• Server stub receives a SOAP request from the
  client stub and converts 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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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
SOAP request
Call client stub
Request service
SOAP response
Client receives result
Result returned
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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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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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Building a ServiceBackground for Web Services
exercise

• 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 Web Services exercise 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 Web Services exercise

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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 Web Services exercise.

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Web Services Exercise

• This assignment uses
• Java 2 platform standard edition
• Apache Jakarta Tomcat Java servlet container
• Apache Axis tools

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Exercise Steps

• Write the Java code to implement the web service.
• Use Axis to generate all needed Java source
  files.
• Compile the source files just generated.
• Create client source and compile.
• Execute client to access service.
• Extend the functionality of the service.

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Axis Java Web Service Facility

• Place a jws (rather than java) file in your web
  application directory structure and Axis will
  automatically find it, compile it, and deploy the
  methods.

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Step 1 Implement Service

• Using Java write the code for the class that
  provides the web service. This code is
• public class MyMath
• public int squared(int x)
• return x x
• Save that code as a .jws (Java Web Service)
  file, Math.jws.

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Step 1 (continued)

• Copy the .jws file to the axis directory
• cp MyMath.jws \
• CATALINA_HOME/webapps/axis/yourusername
• Copying is needed so that the axis tools will be
  able to find the .jws file

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Step 2 Generate WSDL files

• Use the Axis tools to create four Java source
  files from MyMath.jws using the command
• java -classpath AXISCLASSPATH \
• org.apache.axis.wsdl.WSDL2Java \
• http//localhost8080/axis/MyMath.jws?wsdl

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Step 2 (continued)

• Axis finds MyMath.jws file and creates
• Two source files each holding a Java interface,
• MyMath.java and
• MyMathService.java
• Two source files each holding a Java class,
• MyMathServiceLocator.java
• MyMathSoapBindingStub.java
• These files are put in a new package in
• localhost/axis/yourusername/MyMath_jws/
• which is in
• /home/yourusername/WebServices/

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Step 3 Compile new source files

• Compile source files generated by step 2 with
• javac -classpath AXISCLASSPATH \
• localhost/axis/yourusername/MyMath_jws/.java

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Step 4 Write Client Source

• import localhost.axis.yourusername.MyMath_jws.MyMa
  thServiceLocator
• import localhost.axis.yourusername.MyMath_jws.MyMa
  thService
• import localhost.axis.yourusername.MyMath_jws.MyMa
  th
• public class MyMathClient
• public static void main(String args) throws
  Exception
• MyMathService service new
  MyMathServiceLocator()
• MyMath myMath service.getMyMath()
• int x (new Integer(args0)).intValue()
• System.out.println("The square of " args0
  " is "
• myMath.squared(x))

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Step 5 Compile Client code

• Compile the client source file with
• javac -classpath AXISCLASSPATH.
  MyMathClient.java

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Step 6 Execute Web Service program

• java -classpath AXISCLASSPATH MyMathClient 4
• The square of 4 is 16

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Step 7 Extend the Web Service

• Add functionality to the MyMath web service
• Add a method that returns whether a number is
  even.
• Modify MyMath.jws file and repeat all previous
  steps to test the extended web service.

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Extra Credit (not on assignment page)

• For extra credit, create a second web service and
  demonstrate a client using two web services.

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Grid Services Concepts
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Grid service

• The Global Grid Forum (GGF) developed standard
  interfaces, behaviors, core semantics, etc. for
  grid applications based upon web services.
• GGF introduced the term Grid Service as an
  extended web service that conforms to the GGF
  OGSI standard.

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Grid Services

• Standard provides for interoperability of
  independently developed services
• Grid services based on extensions of Web Services

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• The Globus Grid Forum (GGF) standard currently
  divided into
• Open Grid Services Architecture (OGSA)
• and
• Open Grid Services Infrastructure (OGSI)

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Open Grid Services Architecture(OGSA)
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OGSA

• Defines standard mechanisms for creating, naming,
  and discovering Grid service instances.
• Addresses architectural issues relating to
  interoperable Grid services.
• Described in The Physiology of the Grid
• http//www.globus.org/research/papers/ogsa.pdf

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OGSI(Open Grid Services Infrastructure)

• Based upon Grid Service specification and
  specifies way clients interact with a grid
  service (service invocation management data
  interface, security interface, ...).
• Details
• http//www-unix.globus.org/toolkit/draft-ggf-ogsi-
  gridservice-33_2003-06-27.pdf

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Based on http//www.globus.org
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This layer eliminated in most recent version of
standard under development
The core elements of the Open Grid Services
Architecture (shared)
The Grid 2 Blueprint for a new Computing
Infrastructure, Ian Foster, Carl Kesselman and
Steve Tuecker Editors, Morgan Kaufmann 2004 --
Chapter 17 The Open Grid Service Architecture,
by Ian Foster, Carl Kesselman and Steve Tuecker.
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Globus

• Open source grid software toolkit.
• Version 3 includes
• A complete implementation of OGSI
• Additional Web service components, some built on
  top of OGSI.
• We will use Globus 3.2 in Grid Services exercise.

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From http//www.globus.org
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• Grid services concept similar to Remote Procedure
  Call (RPC), Remote Method Invocation (RMI), only
  applied over HTTP
• In fact, Java implementations will use RMI
  underneath.

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Differences between a web service and a grid
service

• Grid services can be
• Stateful or Stateless
• Transient or Non-Transient.
• A web services is usually thought of as
  non-transient and stateless.

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Instances of Grid services

• Clients interact with instances of grid services.
• Apart from being the usual approach in an object
  oriented system, it enables clients to have
  access to different instances of a service and
  provides extended functionality to a web service.
  Allows for transient and private instances.
• Grid Services uses a Factory Service to create
  and manage service instances.

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Grid Services Factory
From http//www.globus.org
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Client - Service Interaction

• One-to-One -- a client has its own instance of
  a service. Most likely, instance destroyed with
  interaction finished.
• One-to-many -- instance of a services
  available to multiple clients. Information from
  service available to multiple clients.

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Grid Service Implementation

• Can be accessed remotely
• Potentially stateful
• Implements one of more WSDL portTypes
• Grid Service Factories can be used to create
  instances of services with many portTypes
• Introspection of a service to return information
  (list of portTypes it implements)

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Next time

• More details on Grid Services and GT3
• It is time to talk about projects.