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Web Services. A good choice for sharing [ocean science] data. Distributed Computing. Connecting systems Transparency Scalability Fault Tolerance. Data Sharing Obstacles. Platforms Languages Transports. Data Sharing Methods. CORBA, RMI, DCOM Problems

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Web services l.jpg

Web Services

A good choice for sharing [ocean science] data.


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Distributed Computing

  • Connecting systems

    • Transparency

    • Scalability

    • Fault Tolerance


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Data Sharing Obstacles

  • Platforms

  • Languages

  • Transports


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Data Sharing Methods

  • CORBA, RMI, DCOM

  • Problems

    • Goals lacked heterogeneous environment

    • Difficult-to-implement

    • Proprietary protocols

    • Not modular – crammed specifications


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The Web Service

Defined: Process between systems

  • Leverage Internet standards

    • Passes XML messages over HTTP

  • Promotes

    • Interoperability

      • Perl to C++ to AppleScript…

    • Loose coupling

      • Implementation-independent & Versioning


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SOAP

  • The Emerging Web Service

    • Interface to existing programs

    • Modular Design

      • Extensible – add-on distinct specs

        • Security

        • Reliability

      • Customizable – combine features as needed

    • No forced model

    • 80+ implementations (platforms,languages)


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SOAP: Requirements

  • Application

  • Application Server

  • SOAP Implementation

  • XML parser (sometimes)


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SOAP: How It Works

  • Calls functions of existing programs

    • Application server knows:

      • Available functions

      • How to decode requests

      • How to encode responses

    • XML Request – invokes a function call

      • With function parameters (if necessary)

    • XML Response

      • Packages returned data of the function


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SOAP: Getting Started

  • Receiving SOAP requests

    • Define a SOAP “Service”

      • Tell Server “Providing” program

      • How to translate data (mapping)

  • Sending SOAP requests

    • Write SOAP call

      • Knowing what you are receiving

      • What parameters to pass along (if necessary)


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SOAP Example

  • Online Address Book

  • Functions:

    • getAddressForName( name )

    • addEntry( <some data> )

    • getAllListings()


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SOAP Response: Notify Server

<isd:service …

id="urn:AddressFetcher">

<isd:provider

type="java" ...

methods="getAddressFromName addEntry getAllListings" …

class="samples.addressbook.AddressBook" …

<isd:mappings>

</isd:service>


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SOAP Request: Making the Call

URL url = new URL("http://ragnarok.whoi.edu:7001/soap/servlet/rpcrouter");

Call call = new Call(); …

call.setTargetObjectURI("urn:AddressFetcher");

call.setMethodName("getAddressFromName");

Vector params = new Vector();

params.addElement( … "John B. Good“ …);

call.setParams(params);

Response response = call.invoke(url);

Parameter ret = response .getReturnValue();

<do something>


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SOAP: In Action

getAddressFromName(“John B. Good”)

Try it

addEntry(“John Doe ...”)

Try it

getAddressFromName(“John Doe”)

Try it

getAllListings()

Try it


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SOAP: Drawbacks

  • Performance

    • XML lacks efficiency of parsing

      • XML Infoset (W3C recommendation)

    • HTTP limitations



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