Advance DBMS Lecture3

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1CPSC608: CORBA Copyright 2000 Hoh In

Lecture #3: CORBA

CPSC608: Distributed Database Systems

January 25, 2000

Hoh InTexas A&M University


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Goals of Today

Understand

CORBA technology: What, Why, How Discuss

Issues of CORBA: promises and problems


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Contents

Review

What is CORBA? Why CORBA? How does CORBA work? What are considerations for using CORBA?

Beyond CORBA


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What is CORBA?

CORBA is a standard for object interoperability

Support for different languages Support for different platforms Communications over the network Additional services (e.g., security)

CORBA is defined by the OMG (Object ManagementGroup) Begin since 1989 CORBA 1 was in 1991 Now, toward to CORBA 3 More information: http://www.omg.org

CORBA is a component of OMA (ObjectManagement Architecture)

* Source: Adapted from www.expede.com


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What is the OMA? Object Model and Interfaces (e.g., Domain Interfaces,

Application Interfaces) Defines what a CORBA object is

Common Object Request Broker Architecture (CORBA) Standard for an ORB (Object Request Broker) Defines the IIOP (Internet Inter-ORB Protocol) -- the standard for

communication Defines the Language interfaces and tools

Object Services -- common services Core services required to develop distributed architectures Naming -- allowing clients to find objects based on names

Trading -- allowing clients to find objects based on their properties

Others: Security, Transactions, event notification, ...

Common Facilities -- high-level services e.g., Distributed Document Component Facility (DDCF) -- OpenDoc Allowing for the presentation and interchange of objects based on a

document model facilitating the linking of a spreadsheet object into areport document


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Some ORBs

CORBA Software

(http://www.infosys.tuwien.ac.at/Research/Corba/software.html) Orbix (IONA) VisiBroker (Inprise) ObjectBroker (BEA)

PowerBroker (Expersoft) ORB Plus (HP) ORBacus (Object-Oriented Concepts, Inc.) NEO/JavaIDL (SunSoft)


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Contents

Review


Beyond CORBA


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Why CORBA?

Need to share information and resources

within and across diverse computingenterprises CORBA is a Middleware Standard

CORBA is a Software Bus CORBA is a Distributed Object Architecture

* Source: Adapted from www.expede.com


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CORBA is a Middleware Standard

Before CORBA, middleware was dominated by proprietary tools

CORBA provides a standard that allows you to: Develop applications using a common basis Change CORBA products with minimal rewriting of code Make objects running on different CORBA products interoperate

Integrate third-party products that respect the standard

CORBA is evolving to standardize other types of middleware

CORBA Object

Middleware

Message-Oriented

Middleware (MOM)

Object TransactionManagement

Transaction

Monitors

* Source: Java-CORBA E. Arch., expede.com


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CORBA and the Software Bus A standard architecture enabling you to plug components into

Support different languages and platforms Connects everything up in a single architecture

A basis for delivering reusable components A CORBA component can be accessed from any client technology A CORBA components has a clearly defined interface



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CORBA and Distributed Architectures



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Contents

Review


Beyond CORBA


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How Does CORBA Work?

Step 1: Write a specification for each object using IDL (Interface

Definition Language) Step 2: Compile the IDL to generate client stub and serverskeleton code

Step 3: Write the client application code. Step 4: Write the server object code.

Step 5: Compile the client and server code Step 6. Start the server Step 7: Run the client application

* Source: Visibroker Progammers Guide


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14CPSC608: CORBA Copyright 2000 Hoh In* Source: Visibroker Progammers Guide

12

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IDL

InterfaceDefinitionLanguage

IDL is a purelydeclarativelanguage Looks like a Java

Interface Independent from

any programminglanguage

Basic Types No int type No pointer type

* Source: expede.com and Supplemental Reading #19-1


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VisiBroker Demo


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Contents

Review


Beyond CORBA


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What are considerations for usingCORBA?

Security Performance Fault-Tolerance Scalability


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How to Analyze Security in CORBA?

The CORBA Security Service specification

Identification and authentication: verify who they claim to be Authorization and access control: decide whether an objectcan be accessed or not

Security auditing: make users accountable for security Security of communication between objects

Non-repudiation

The CORBA ORB-SSL integration specification The CORBA/Firewall specification

TCP/IP firewalls

SOCKS v5.0 firewalls GIP proxy firewalls


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How to Analyze Performance in CORBA?

Factors having a strong influence on the performance

of a distributed system The number of remote method invocations that are made

within the system The amount of data that is transferred with each remote

method invocation The marshalling costs of the different IDL data types used by

the system


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Fault Tolerance in CORBA

Failures caused by factors as diverse as:

Loss of processing resources - hardware or software Loss of logical and physical communication paths -- networkand connectivity failures

Both transient and permanent failures in the application itself

Approaches Prevention is better than cure Accept the fact that processes dont stay up for ever Complex heterogeneous applications are combined from

many tool components

CORBA Support Cold replication model Warm standby model Hot standby model


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Cold Replication Model

* source: Reference [3}


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Warm Standby Model



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Hot Standby Model



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Scalability Issues in CORBA

If a large number of client application is concurrently

executed using any CORBA system, consider: Will this single host have enough processing power tosupport all these clients?

Our manager server is a single point of failure. How will oursystem handle a software or hardware fault?

Our manager server process is limited to approximately1000 connections. How will the remaining clients be able toconnect to this process?

Approaches

Replicating severs Closing connections Load balancing (e.g., using application partitioning or

replication mechanisms)


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Contents

Review


Beyond CORBA


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Beyond CORBA

Unnecessary Heavy

Services Some application dontneed all services thatCORBA provides. Theymay degrade performancewithout any gains.

A solution approach:Container = objects +selected services

Scalability of ORB global Naming protocol complex marshalling

* Source: Enterprise CORBA


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Advance DBMS Lecture3