Seminarium onComponent-based Software Engineering

Jan Willem Klinkenberg

CORBA

22/04/23 Seminarium CBSE 2

Object Management Group (OMG) Consortium of Computing Industry Founded in 1989 Non profit around 800 members Goal: standardization of “whatever it

takes” to achieve interoperability on all levels of an open market for “objects”

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OMG Original effort: fix “wiring” problem:

How can distributed object-oriented systems implemented in different languages and running on different platforms interact?

Incompatibility between compilers Differences in object models Differences in platforms

Solution: CORBA

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CORBA Common Object Request Broker

Architecture. Open standard 1991 – version 1.0

Initial version. 1995 – version 2.0

IIOP OMA More languages support

2002 – version 3.0 Corba Component Model (CCM) Scripting languages support

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CORBA CORBA - Common Object Request

Broker Architecture.

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IDL Interface Definition Language

Defines all object interfaces in a common language Bindings are available for C, C++, Java, Python,

Smalltalk, Cobol, etc… An IDL compiler generates stubs and skeletons.

Stubs:• Looks like local object• Marhals arguments• Forwards all invocations through ORB to target object

Skeletons:• Receives invocations from ORB• Unmarshals arguments• Invokes target methods• Sends back return value

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IDL – examplemodule Example {

struct Date {unsigned short Day;unsigned short Month;unsigned short Year;

};interface Ufo {

readonly attribute unsigned long ID;readonly attribute string Name;readonly attribute Date FirstContact;unsigned long Contacts();void RegisterContact(out Date

dateOfContact);};

};

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IDL types IDL distinguishes between basic and

constructed type and CORBA object references.

Before CORBA 2.3, only references Since CORBA 2.3, call by value is

supported -> standard mapping by XML

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DII and DSISometimes binding can be too static:

DII Dynamic invocation interface DSI Dynamic skeleton interface (since

Corba 2.0)

These interfaces allow for dynamic selection of methods at client side or server side

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ORB Object Request Broker

Routes the method invocations Interface repository Implementation repository Can load and start object servants Can communicate with other ORBs using

IIOP

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CORBA and OMG IDL

Dynamicinvocationinterface

IDLstubs

ORBinterface

Object Adapter

Object Request Broker (ORB)

ApplicationsPrograms

IDLcompiler

Objectservants

IDLSkeletons

DynamicSkeletoninterface

IDL source

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Object Adapter Object servants register with ORB via the

object adapter. Servants are loaded and started by ORB via

adapter. BOA – Basic Object Adapter

Under specified, deprecated in 1998 POA – Portable Object Adapter

Replaced the BOA Essential for several CCM features Creates object references Several possible policies for object creation

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Server, client or both Separation of client and called object

does not impose an asymetric architecture.

The same process can issue and receive calls.

Pure application programs do not require registration with ORB

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CORBA v.1 - Problems An ORB is essentially an remote

incovation service Replaces sockets and remote

procedure calls in distributed applications with a cleaner model

So what’s the problem? Applictions still have to share many

conventions to interoperate OMG had to broaden it’s focus.

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OMA - Object Management Architecure Since CORBA 2.0 Adds new areas of standardization:

CORBAservices Common object services e.g.: naming, trader

event, security CORBAfacilities – defines a specific component

framework than can be used to integrate components. Horizontal: domain independent, focus on

specific application models e.g. printing facilities Vertical: domain specific e.g. healtcare, finance

Application object specifications (currently void) CCM - CORBA Component Model (since 3.0)

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CORBA Services supporting enterprise distributed computing Naming service

White pages Trader service

Yellow pages Event service

Send event objects from event suppliers to event consumers.

Notification service Add QoS, filtering, etc. to Event service

Object transaction service Security Service

Encryption, authentication

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CORBA Services supporting architecture using fine-grained objects Concurrency control service

Lock and release resources Licensing service

For non-freeware objects Lifecycle service

Creation, copying, moving and deletion of objects

Relationship service Not used or implemented

Persistant state service Allows storing and retrieving of objects

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CORBA Services continued… Externalization service

Mapping of object into stream and back Properties service

Add/delete and retrieve arbitrary properties to objects

Object query service (not implemented) Locate object instance by attributes

Object collections service (not implemented) Provides collection types like sets, trees, queues or

lists. Time service

Provides a universal time for the distributed system

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CCM - Corba Component Model Introduced with CORBA 3.0 in 2002 Logical extension of Enterprise

JavaBeans Is an architecture for defining

components and their interactions Provides a packaging technology Provides a container implementation

framework (CIF)

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CCM Component

MyBusinessComponent

Component interface

Facets

Eventsources

Eventsinks

Attributes

Receptacles

OFFERED

REQUIRED

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CCM Components features Ports

Facet – provided interface Receptacle – required interface Event sources Event sinks

Primary keys Instance identification for client

Attributes Home interfaces

Provides factory functionality

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CCM packagingCCM Assembly

CCM Component

Segments

Deployment configuration

CCM Component

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CCM Containers Component instances are placed

inside containers:

Component C

Home interface

Callbacks Services

Components interact with POA as well as transaction, security, persistence and notification services via interfaces on their container

Home for C

Container

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Components types There are different types of

components: Service Session Entity Process

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CIF Component Implementation

Framework Described in CIDL, Component

implementation Definition Language Creates programming skeletons that

automate many of the basic behaviors of components, including navigation, identity inquiries, activation, state management, lifecycle management, and so on.

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Questions?

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