Slide 1 © Ingeniørhøjskolen i Århus ITONK1 CORBA & ICE Introduction.

© Ingeniørhøjskolen i Århus

ITONK1

CORBA & ICE Introduction


Goals of this lesson

• After this 2x35 min. lesson you will be:• Introduced to CORBA and ICE• Ready to present their position in the Middleware technology

family, when and where to use it

• You will not:• Be an expert. More practice and theory is required


Outline

• CORBA & ICE• Introduction & Background

• Architecture

• Session & Presentation layer

• CORBA Interface Definition Language – IDL

• ICE IDL: Slice

• Language mappings


CORBA Organization• OMG: Object Management Group

• http://www.omg.org • Non-profit organization in the US, representatives in United

Kingdom, Germany, Japan, India, and Australia• Founded April 1989• More than 800 members• Dedicated to creating and popularizing object-oriented industry

standards for application integration, e.g.• CORBA 1.0 (1995) –> CORBA 3.0.3 (2006)• UML 1.1 nov. 97. -> 2.1 (2006)


Goal of CORBA• CORBA: Common Object Request Broker Architecture

• Support distributed and heterogeneous object request in a way transparent to users and application programmers

• “King” of OO-Middleware

• Facilitate the integration of new components with legacy components (COBOL, C, ADA, C++, C#, Delphi, Python)

• Open standard that can be used free of charge

• Based on wide industry consensus • But not much Microsoft support


CORBA Problems

• Problem with CORBA• Considered too complex by many• Open standards -> cluttered solutions• No Microsoft Support • Is CORBA dead?


The Specifications

• CORBA is a collection of specifications• http://www.omg.org/technology/documents/corba_spec_catalog.htm

• Common Object Request Broker Architecture (CORBA/IIOP) (3.0.3)• CORBA Component Model (3.0)• Light Weight CCM• CORBA/e (replaces Minimum CORBA)• Real-Time CORBA (Dynamic/Static Scheduling)• Families of specifications:

• CORBAservices Specifications • CORBAfacilities Specifications • OMG Domain Specifications • IDL / Language Mapping Specifications

• Many others• Realted to UML

• UML Profile for CORBA (1.0)


CORBA History

• CORBA 1.0 (October 1991): IDL, C mapping• CORBA 1.1 (February 1992): BOA• CORBA 1.2 (December 1993): minor updates• CORBA 2.0 (August 1996): DSI, GIOP, IIOP, C++, SmallTalk

mappings• CORBA 2.1 (August 1997) : Secure IIOP / SSL, COBOL, ADA

mappings• CORBA 2.2 (February 1998): POA, Java mapping• CORBA 2.3 (June 1999): Objects by Value• CORBA 2.4 (October 2000) : INS & Interop services• CORBA 2.5 (September 2001) : Real-time CORBA• CORBA 2.6 (December 2001) : Common Security• CORBA 3.0 (July 2002): CCM, Minimum CORBA• CORBA 3.0.2 (December 2002): Minor Updates


ICE Background & History

• ICE: Internet Communication Engine• Group of ex CORBA specialists:

• Standard committees is ruining CORBA

• We need to “start-over”

• GPL – but controlled by one company

• ZeroC.com

• 2003: ZeroC announces ICE 1.01


ApplicationObjects

CORBAFacilities

CORBA Services(mandatory)

DomainInterfaces

Object Management Architecture (OMA)

Object Request Broker


CORBA Architecture1• Many different vendors and ORB types• Many of which do not interoperate• Must check specification compliance• OrbBacus from IONA produces both C++ and Java• Sun J2SE SDK has only Java-based ORB• C++ ORB from IONA will work with SUN ORB as specified• Many others

• MicoORB, Middcor, TAO, openORB, VisiBroker• OmniORB• OrbExpress: FPGA hardware ORB!


One standardised interface

One interface per object operation

ORB-dependent interfaceOne interface per object adapter

DynamicInvocation

ClientStubs

ORBInterface

Implementation Skeletons

Client Object Implementation

ORB Core

ObjectAdapter

CORBA Architecture 2


ICE Architecture


CORBA 2.0

Applications

GIOP ESIOP

IIOP DOETalk ........ DCE-CIOP ........

Mandatory: provides "out of the box" interoperability

Interoperability Protocols

EnvironmentSpecific ..

IIOP: Internet Inter-ORB Protocol is the primary CORBA transport protocol


General Inter-ORB Protocol (GIOP)

• Handles the session & presentation layer• Defines seven message primitives:

• Request, Reply, Locate Request, Locate Reply, Cancel request, Close Connection, Message Error

• More simple than JRMP for Java RMI

• Internet Inter-ORB Protocol (IIOP)

• Maps GIOP to TCP/IP• Provides operations to open and close TCP/IP connections• Is required from ORBs for CORBA compliance• But intra vendor ORB com is not restricted to this

More on the IIOP later in the course


Common Data Representation (CDR)

• Defined as part of GIOP• Presentation layer implementation to support

heterogeneity• Mapping of IDL data types to transport byte stream• Encodings of

• primitive types

• constructed types

• interoperable object references


Recap - motivation for an IDL

• IDL: Interface Definition Language • Components of distributed systems are written in

different programming languages• Programming languages may or may not have their

own object model• Object models largely vary• Differences need to be overcome in order to facilitate

integration


Heterogeneous OO Network

CORBAC++

ClientApp.3

CORBAC#

ClientApp.2

CORBAJavaClientApp.1

TCP/IPNetwork

CORBACobol

DatabaseServer

DB

“Object Wrapping

of nonOO application”

Different ORB’s from different vendors, on different operating systems – and written in different languages = Heterogenity


PL6

PL2

PL5

PL1

PL4

PL3 PL6

PL2

PL5

PL1

PL4

PL3IDL

CORBA IDL & Mappings

Avoid multiple mappings


IDLCommon

ObjectModel

SmalltalkSmalltalk

CobolCobol

JavaJava

Ada-95Ada-95C++C++

CC

CORBA Programming Language Bindings

.NET.NETJaneva / Middcor (C#)Janeva / Middcor (C#)

Win32 DelphiWin32 Delphi


ICE Language Support

• C++• Java• .NET• Python• PHP• Objective C• Ruby


Interface Definition Language (IDL)

• Language for expressing all concepts of the middleware’s object model

• Should be• programming-language independent

• not computationally complete

• Bindings to different programming languages are needed • language bindings are specified by CORBA

The IDL is very comprehensive – don’t try to learn everything

The IDL of ICE is called SLICE


Example UML to IDL mapping

Player

-name:string-Number:int

+book()

Team

-name:string

+bookGoalies()

plays in

1 11..16

+transfer(p:Player)

Club

-noOfMembers:int-location:Address

has1

*

uses

Organization

#name:string

coaches 1..*

1..*

Trainer

-name:string1 1..*

+train()works for


Constructed types

CORBA Object Model: Types

typedef struct Address {

string street;

string postcode;

string city;

};

typedef sequence<Address> AddressList;

interface Team { ... };

Atomic types

Object type


CORBA Object Model: Modules

module Soccer { typedef struct Address { string street; string postcode; string city; };};module People { typedef struct Address { string flat_number; string street; string postcode; string city; string country; };};

Modules =namespaces

Soccer::Address

People::Address


CORBA Object Model: Attributes

interface Player;

typedef sequence<Player> PlayerList;

interface Trainer;

typedef sequence<Trainer> TrainerList;

interface Team {

readonly attribute string name;

attribute TrainerList coached_by;

attribute Club belongs_to;

attribute PlayerList players;

...

};

Attribute type Attribute name

changeable

Clients cannotchange value


CORBA Object Model: Operations

interface Team {

...

void bookGoalies(in Date d);

string print();

};

Parameter list

Parameter kind

Parameter type

Parameter nameOperation nameused in requests

Return types


CORBA Object Model: Exceptions• Generic Exceptions (e.g. network down, invalid object

reference, out of memory)• Type-specific Exceptions (e.g. PlayerBooked)

exception PlayerBooked{sequence<Date> free;}; interface Team { void bookGoalies(in Date d) raises(PlayerBooked); };

Exception data

Operations declareexceptions they raise

Exception name


CORBA Object Model: Subtypes

interface Organization { readonly attribute string name; };interface Club : Organization { exception NotInClub{}; readonly attribute short noOfMembers; readonly attribute Address location; attribute TeamList teams; attribute TrainerList trainers; void transfer(in Player p) raises NotInClub; };

Inherited by Club

Supertype

Implicit supertype: Object

This has only been a minimal presentation of the IDL


ICE vs CORBA Comparision

• Performance is equal• Appears easier than CORBA• CORBA is based on standards and is open and

widely supported• ICE has ”one environment for all” – but is controlled

by ZeroC• ICE is GPL with all bindings• Hard to find both C++, Java and .NET CORBA in one

product

Slide 1 © Ingeniørhøjskolen i Århus ITONK1 CORBA & ICE Introduction.

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