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Distributed Object Computing

Team - A1

Williamson, MacFarlane, Crabtree

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SOAP Introduction

• Need exists for truly interoperable standards for object access.

• XML and HTTP provide perfect infrastructure.

• SOAP – Simple Object Access Protocol provides a lightweight protocol for remote object access with an eye on extensibility and simplicity.

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SOAP Process

• Sender initiates communication using an HTTP post with XML (SOAP) content

• Receiver processes SOAP message and returns result via HTTP response

• Errors are returned as a SOAP Fault

• SOAP allows for intermediaries

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SOAP Structure

• SOAP Envelope– The wrapper for the SOAP message

• SOAP Header(s)– Contain processing information and requirements– Allows for application-specific extensibility– Used to instruct intermediaries

• SOAP Body– Actual SOAP payload intended for the recipient– May contain SOAP Fault

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SOAP & RPC

• A non-vendor specific, non platform-specific way to conduct RPC

• Represent method calls using specially-formatted SOAP XML

• Supports advanced advanced language features such as polymorphism and function overloading

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SOAP Extensions

• WSDL– Web Services Description Language– A published interface for a web service

• UDDI– Directory of web services– A searchable “yellow pages” of WSDL

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What is an ORB

• Stubs and Skel utilize IDL• IIOP is layered upon the Internet• ex: CORBA, DCOM, EJB

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DCOM-General Info.

• DCOM (Distributed Component Object Model), from Microsoft, is an extension of COM for distributed environments.

• Provides client-server communications• Comes packaged with Windows Operating

systems and is available for major UNIX platforms and IBM’s large server products.

• DCOM replaces OLE Remote Automation.

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DCOM-Technical Info.

• Uses TCP/IP and HTTP

• Object RPC (ORPC), an extension of the DCE RPC protocol, defines how remote procedure calls are made across a network.

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RPC Structure

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DCOM Architecture

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Extending ORBs

• Real-Time– Configurability

– Predictability

– High Peformance

– Assurance of Correctness

– Resource Management

– Prioritization Issues

• Fault Tolerance– Active/Passive

Replication

– Network Recovery

– Fault Detection

– Rollback and Recovery

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Eternal - Unmodified ORB

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DOORS

UnmodifiedORB

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DCE

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DCE (cont)