Distributed Object Computing using XML-SOAP

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Distributed Object Computing using XML-SOAP

• Kevin White
• James Kebinger
• Fall 2000

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Introduction to XML

• XML it s a text-based markup language that is
  becoming a standard to store data
• XML tags tell you what the data means, rather
  than how to display it.
• Elements are the holding blocks for data in an
  XML object.

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XML Example

• The following is a XML example of a pizza item
• ltpizzagt
• ltnamegtThe Texanlt/namegt
• lttoppingsgt
• lttoppinggtbarbeque brisketlt/toppinggt
• lttoppinggtdill pickleslt/toppinggt
• lttoppinggtonionslt/toppinggt
• lttoppinggtmozzarella cheeselt/toppinggt
• lttoppinggttomato saucelt/toppinggt
• lt/toppingsgt
• ltdescriptiongtPut the lone in lone star
  state!lt/descriptiongt
• lt/pizzagt

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What is XML?

• XML objects can also consist of the following
  items
• Elements holding blocks for data
• Attributes Name-value pairs that occur inside
  start-tags after the element name.
• Entity references Created to allow entity to be
  created and used in places where multiple
  instances of the same text will be use in many
  places.
• Processing instructions used to provide
  information specific to applications.
• Comments User comments
• CDATA A section of character data that will not
  be interpreted by the XML parser.

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Why is XML important?

• Plain Text
• XML is it stored as plain ASCII text
• Allows for viewing and editing the XML data with
  any text editor
• Data Identification
• Tag names relate to the data it holds
• Produces easily parable data with reference to
  tag names

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Why is XML important?

• Display styles
• XML is only a way to store data. A separate file
  can be created to display this data
• XSL
• Hierarchical
• XML documents benefit from their hierarchical
  structure
• Like stepping through a table of contents

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Present Distributed Object Models

• Java RMI for Java applications
• DCOM for Windows applications
• CORBA for cross platform applications
• Each have overhead and large scale
  interoperability issues
• Answer SOAP Simple Object Access Protocol

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Java RMI

• Design goal for the RMI architecture was to
  create a Java distributed object model
• RMI works in 3 layers
• The first layer intercepts method calls made by
  the client and redirects these calls to a remote
  RMI service.
• This second layer understands how to interpret
  and manage references made from clients to the
  remote service objects.
• The final layer is the transport layer and is
  based on TCP/IP connections between machines in a
  network.
• Java RMI works for Java applications only

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DCOM

• DCOM Distributed Component Object Model
• Microsofts solution for distributed computing
• Allows one client application to remotely start a
  DCOM server object on another machine and invoke
  its methods
• DCOM provides the ability to use and reuse
  components dynamically, without recompiling, on
  any platform, from any language, at any time

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CORBA

• CORBA Common Object Request Broker Architecture
• CORBA is platform and language independents
• CORBA Object Request Broker (ORB) provides a way
  to connect a client application with an object
  that it needs
• When creating CORBA applications, two main
  classes, a stub and a skeleton, are created along
  with several helper classes
• The ORB is the glue that connects the stubs and
  skeletons.

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The SOAP Protocol

• SOAP stands for Simple Object Access Protocol
• SOAP doesn't care what operating system,
  programming language, or object model is being
  used on either the server side or the client side
  
• SOAP is a cross-platform way to make remote
  method calls, serialize and de-serialize objects
  using XML

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The SOAP Protocol

• For a protocol it commonly uses HTTP, which is
  simple to implement and used universally
• SOAP works over many protocols, not limited to
  HTTP
• Using HTTP for transport gives SOAP an advantage
  over other previous middleware solutions because
  it does not require changes be made to network
  routers and proxy servers
• An inherent advantage of SOAP being able to use
  HTTP is that it is a universally deployed
  protocol

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SOAP Process

• SOAP request would be processed in the following
  steps
• 1. Get a request on the listen port.
• 2. Parse the request for the method id to call.
• 3. Consult a configuration file for what
  class/function to call to handle the request.
• 4. De-serialize the parameters for the method
  call.
• 5. Call the function with the given de-serialized
  parameters
• 6. Serialize the return value from the function
  and send it back to the requestor
• SOAP is not rocket-science. SOAP is simple to
  understand, implement and deploy.

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Basic SOAP Sample

• Here is a SOAP request
• POST /StockQuote HTTP/1.1Host
  www.stockquoteserver.comContent-Type text/xml
  charset"utf-8"Content-Length nnnnSOAPAction
  "Some-URI"ltSOAP-ENVEnvelope  xmlnsSOAP-ENV"h
  ttp//schemas.xmlsoap.org/soap/envelope/"  SOAP-E
  NVencodingStyle"http//schemas.xmlsoap.org/soap/
  encoding/"gt   ltSOAP-ENVBodygt       ltmGetLastTr
  adePrice xmlnsm"Some-URI"gt           ltsymbolgtDI
  Slt/symbolgt       lt/mGetLastTradePricegt   lt/SOAP
  -ENVBodygtlt/SOAP-ENVEnvelopegt

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Basic SOAP Sample

• And the matching response is
• HTTP/1.1 200 OKContent-Type text/xml
  charset"utf-8"Content-Length
  nnnnltSOAP-ENVEnvelope  xmlnsSOAP-ENV"http//
  schemas.xmlsoap.org/soap/envelope/"  SOAP-ENVenc
  odingStyle"http//schemas.xmlsoap.org/soap/encodi
  ng/"/gt   ltSOAP-ENVBodygt       ltmGetLastTradePr
  iceResponse xmlnsm"Some-URI"gt           ltPricegt
  34.5lt/Pricegt       lt/mGetLastTradePriceResponsegt
     lt/SOAP-ENVBodygtlt/SOAP-ENVEnvelopegt

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Apache SOAP

• Used Apache SOAP v 2.0 for implementation.
• Java library for both client and server
• Application need not parse nor create XML
• Server implemented as a servlet
• Server application programmed without regard to
  SOAP
• Client SOAP calls easy to construct using API

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SOAP National Bank

• Prototype client-server application
• Supports basic banking tasks
• Balance inquiries
• Deposits/withdrawals
• Transfers
• View transaction history

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Use Cases
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Class Diagram
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System Architecture
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System Implementation

• Client and Server written in Java v 1.22
• Client GUI uses Java Swing API
• Server uses JDBC to connect to MS Access DB
• Client and Server communicate using Apaches Java
  SOAP library

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Screenshot
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Bank System Conclusions

• System successful, all functions work
• Implementation fairly painless once we learned
  SOAP API
• Only major snag was learning how to configure the
  SOAP servlet
• Application rather slow what causes slowness?
• MS Access calls
• SOAP itself

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SOAP Benchmarking

• Compare RMI to SOAP
• Build a small client-server system to exchange
  the current data and time
• As a java.util.Date object
• As a java.lang.String object
• Different objects will compare efficiency and
  scalability of serialization

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SOAP Serialization Example

• String
• ltreturn xsitype"xsdstring"gtThu Nov 23 172446
  EST 2000
• lt/returngt

• Date
• ltreturn xsitype"ns1date"gt
• lttime xsitype"xsdlong"gt975013920065lt/timegt
• ltminutes xsitype"xsdint"gt12lt/minutesgt
• ltseconds xsitype"xsdint"gt0lt/secondsgt
• ltdate xsitype"xsdint"gt23lt/dategt
• ltday xsitype"xsdint"gt4lt/daygt
• lthours xsitype"xsdint"gt16lt/hoursgt
• ltyear xsitype"xsdint"gt100lt/yeargt
• lttimezoneOffset xsitype"xsdint"gt300lt/timezoneOf
  fsetgt
• ltmonth xsitype"xsdint"gt10lt/monthgt
• lt/returngt

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Benchmark Setup

• 250 Remote Calls per trial
• Took average of 3 trials for final results
• Tests run on Pentium 2 266 Laptop with 288 Megs
  of RAM
• Tests run locally, therefore do not reflect cost
  of network time.

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SOAP Serialization
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RMI Serialization
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RMI v. SOAP
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Benchmark Conclusions

• RMI about ten times faster than SOAP
• Agrees with published results from Indiana
  University
• RMI Serialization may scale better than SOAP
• SOAP using possibly inefficient generic
  serializer in test

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SOAP Conclusions

• SOAP could use an automatic stub generator like
  RMI
• Would have sped up development greatly
• Lots of people using SOAP
• IBM, Microsoft, Compaq etc.
• SOAP not a standard yet
• Could change a lot before settling down

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SOAP Conclusions

• SOAP very usable today
• Some questions concerning interoperability
  between SOAP implementation
• SLOW
• May be OK for some web apps
• Not for high performance computing
• Would recommend use for small systems