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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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Presentation Transcript
web services

Web Services

A good choice for sharing [ocean science] data.

distributed computing
Distributed Computing
  • Connecting systems
    • Transparency
    • Scalability
    • Fault Tolerance
data sharing obstacles
Data Sharing Obstacles
  • Platforms
  • Languages
  • Transports
data sharing methods
Data Sharing Methods
  • CORBA, RMI, DCOM
  • Problems
    • Goals lacked heterogeneous environment
    • Difficult-to-implement
    • Proprietary protocols
    • Not modular – crammed specifications
the web service
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
slide6
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)
soap requirements
SOAP: Requirements
  • Application
  • Application Server
  • SOAP Implementation
  • XML parser (sometimes)
soap how it works
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
soap getting started
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)
soap example
SOAP Example
  • Online Address Book
  • Functions:
    • getAddressForName( name )
    • addEntry( )
    • getAllListings()
soap response notify server
SOAP Response: Notify Server

id="urn:AddressFetcher">

type="java" ...

methods="getAddressFromName addEntry getAllListings" …

class="samples.addressbook.AddressBook" …

soap request making the call
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();

soap in action
SOAP: In Action

getAddressFromName(“John B. Good”)

Try it

addEntry(“John Doe ...”)

Try it

getAddressFromName(“John Doe”)

Try it

getAllListings()

Try it

soap drawbacks
SOAP: Drawbacks
  • Performance
    • XML lacks efficiency of parsing
      • XML Infoset (W3C recommendation)
    • HTTP limitations
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