CS551 - Lecture 101

CS551 Object Oriented Middleware (II) (Chap. 4 of EDO)

Yugi LeeSTB #555(816) 235-5932yugi@umkc.eduwww.sice.umkc.edu/~leeyu

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Outline

• CORBA– CORBA Object Model– CORBA Interface Definition Language (IDL)– CORBA Architecture

• COM– Common Object Model– Microsoft IDL– COM Architecture

• RMI– Java (RMI) Object Model– Interface Definition in Java– RMI Architecture

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Who is the Object Management Group (OMG)?• Non-profit organization with HQ 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– ODMG-93– UML

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Goal of CORBA

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

• Facilitate the integration of new components with legacy components

• Open standard that can be used free of charge• Based on wide industry consensus

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Application Objects

CORBAfacilities

CORBAservices

DomainInterfaces

Object Request Broker

Object Management Architecture

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Object Model and Interface Definition

• Objects• Types• Modules• Attributes• Operations• Requests• Exceptions• Subtypes

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OMG Interface Definition Language

• Language for expressing all concepts of the CORBA object model

• OMG/IDL is– programming-language independent– orientated towards C++– not computationally complete

• Different programming language bindings are available

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Running Example

Team-name:string+bookGoalies()

coaches 1..*1..*

Player-name:string-Number:int+book()

+transfer(p:Player)

Club-noOfMembers:int-location:Address

Trainer-name:string

Organization#name:string

works for1 1..*

uses

plays in1 11..16

has1

*

+train()

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CORBA Object Model: Objects

• Each object has one identifier that is unique within an ORB (Object Request Broker)

• Multiple references to objects• References support location transparency• Object references are persistent

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CORBA Object Model: Types

typedef struct _Address { string street; string postcode; string city;} Address;typedef sequence<Address> AddressList;interface Team { ... };

Atomic types

Object type

Constructed types

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CORBA Object Model: Modules

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

ModulesSoccer::Address

People::Address

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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

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CORBA Object Model: Operations

interface Team { ... void bookGoalies(in Date d); string print(); };

Parameter list

Parameter kind

Parameter typeParameter nameOperation name

used in requests

Return types

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CORBA Object Model: Requests

• Requests are defined by client objects• Request consist of

– Reference of server object– Name of requested operation– Actual request parameters– Context information

• Request is executed synchronously• Requests can be defined

– statically– dynamically

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CORBA Object Model: Exceptions

• Generic Exceptions (e.g. network down, invalid object reference, out of memory)

• Type-specific Exceptions

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

Exception data

Operations declareexceptions they raise

Exception name

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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

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One standardised interfaceOne interface per object operation

ORB-dependent interfaceOne interface per object adapter

DynamicInvocation

ClientStubs

ORBInterface

Implementation Skeletons

Client Object Implementation

ORB Core

ObjectAdapter

CORBA Architecture

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Goals of COM

• Provide a component object model that facilitates binary encapsulation and binary compatibility– Binary encapsulation: Clients do not have to be re-

compiled if server objects change– Binary compatibility: Client and server objects can be

developed with different development environments and in different languages

• COM is proprietary de-facto standard

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Object Model and Interface Definition

• Interfaces• Implementations and Objects• Classes• Attributes• Operations• Requests• HRESULTS• Inheritance

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Microsoft IDL (MIDL)

• Language for expressing all COM concepts• MIDL is

– programming-language independent– evolved from OSF/RPC IDL– not computationally complete

• Different programming language bindings are available• Explanation of Model and Language by same example

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COM Interfaces

[object, uuid(1CF2B120-547D-101B-8E65-08002B2BD118)]interface IOrganization : IUnknown { ...};[object, uuid(1CF2B120-547D-101B-8E65-08002B2BD116)]interface IClub : IOrganization { ...};

UUID

Interfaces

Interface Inheritance

Root Interface

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COM Implementations

• Implement Interface in Prog. Lang., e.g. C++#include "Soccer.h"class Player : public IPlayer { private: char* name; short Number; protected: virtual ˜TrainerPlayer(void); public: TrainerPlayer(void); IMPLEMENT_UNKNOWN(TrainerPlayer) BEGIN_INTERFACE_TABLE(TrainerPlayer) IMPLEMENTS_INTERFACE(ITrainer) IMPLEMENTS_INTERFACE(IPlayer) END_INTERFACE_TABLE(TrainerPlayer) void book(); // IPlayer methods};

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COM: Objects

• Instances of COM Implementations• References to COM objects are called interface

pointers• Interface pointers refer to main memory locations• References support location transparency• Object references are persistent

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COM Classes

• Named implementations• Have one or several interfaces• Are the principal mechanism to create COM

objects• Can return interface pointers to specific COM

objects

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implements

1..*

1..*

Interfaceuuid : GUID

implements

instantiates 0..*1

Implementation

1..*

instantiates

11

Classclsid : GUID

1..*

0..*

Objectlocation : int

0..*1

creates&locates

ClassObject

11

0..*

COM Objects, Interfaces and Classes

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COM: Attributes

• COM does support attributes• Attributes must be represented as set and get

operations by the designer• COM has a keyword to designate this• Example:interface IOrganization : IUnknown { [propget] HRESULT Name([out] BSTR val);};

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COM: Operations

interface IClub : IOrganization { [propget] HRESULT NoOfMembers([out] short *val); [propget] HRESULT Address([out] ADDRESS *val); [propget] HRESULT Teams([in] long cMax, [out] long *pcAct, [out,size_is(cMax),length_is(*pcAct)] ITeam *val); [propput] HRESULT Teams([in] long cElems, [in,size_is(cElems)] ITeam *val); [propget] HRESULT Trainers([out] ITrainer *val[3]); [propput] HRESULT Trainers([in] ITrainer *val[3]); HRESULT transfer([in] IPlayer *p);};

Operation name

Parameter listParameter kind

Return value indicating success/failure

Parameter, e.g.Interface pointer

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31 30-29 28-16 15-0

COM: HRESULTS

• HRESULTS are 32-bit integers• Structured into four fields

SeverityCode Reserved

FacilityCode

InformationCode

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COM Operation Invocations

• Invocation is defined by client objects• Invocation determines

– Interface pointer of server object– Name of invoked operation– Actual parameters

• Invocation is executed synchronously• Invocation can be defined

– statically– dynamically

• Clients have to interpret HRESULTS!

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Three Implementations of Requests

Inter-process call withlight-weight RPC

Method call

Client Object

Local Object inIn-Process DLL

Local Objectin EXE Server

Object onRemote Host

Remote call withreal RPC

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COM Architecture

ObjectProxy

COMLibraryInterface

proxy

Client

Objectstub

COMLibraryInterface

stub

SCMRegistry

SCMRegistry

OXIDResolver

OXIDResolver

Microsoft RPCsOXIDObject

ApplicationLayer

PresentationLayer

SessionLayer

Server

Implementation

COM Class

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COM Architecture

• Application Layer: – Client object: has a pointer to an interface proxy– an implementation of the interface and a COM class (creating new instances of

the implementation and locate these instances)• Presentation Layer: (un)marshalling

– (un)marshalling interface pointers and create an interface proxy for a requested interface (object proxy, object stub)

– (un)marshalling and unmarshalling the parameters of all operations contained in the interface (interface proxy, interface stub)

• Session Layer: – object activation: SCM (Service Control Manager)– the mapping of interface pointers to RPC bindings and references of server

objects for remote method invocation, OXID (Object Exporter Identifier) resolver

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Goals of RMI

• In Java 1.0 object communication confined to objects in one Virtual Machine

• Remote Method Invocation (RMI) supports communication between different VMs, potentially across the network

• Provide tight integration with Java• Minimize changes to Java language/VM • Work in homogeneous environment

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Java Object Model

• Interfaces and Remote Objects• Classes• Attributes• Operations• Exceptions• Inheritance

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Java Interfaces and Remote Objects

• Java already includes the concept of interfaces• RMI does not have a separate interface definition

language• Pre-defined interface Remote• Remote interfaces extend Remote • Remote classes implement remote interfaces• Remote objects are instances of remote classes

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Java Remote Interface Example

package soccer;interface Team extends Remote {public: String name() throws RemoteException; Trainer[] coached_by() throws RemoteException; Club belongs_to() throws RemoteException; Players[] players() throws RemoteException; void bookGoalies(Date d) throws RemoteException; void print() throws RemoteException;};

Remote operations

Interface nameDeclare it as remote

Package name

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Attributes

• RMI does not attributes• Attributes must be represented as set and get

operations by the designer• Example:interface Club extends Organization, Remote {public: int noOfMembers() throws RemoteException; Address location() throws RemoteException; Team[] teams() throws RemoteException; Trainer[] trainers() throws RemoteException; ...};

Attribute get operations

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Combining Classes and Remote Interfacesinterface Organization { private: String name() RemoteException;};class Address { public: String street; String postcode; String city;};interface Club extends Organization, Remote { public: int noOfMembers() throws RemoteException; Address location() throws RemoteException; Team[] teams() throws RemoteException; Trainer[] trainers() throws RemoteException; void transfer(Player p) throws RemoteException;};

Club makes name() remotely accessible

Club can return an address object

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Parameter Passing

• Atomic types are passed by value• Remote objects are passed by reference• Non-Remote objects are passed by value

class Address { public: String street; String postcode; String city;};interface Club extends Organization, Remote { public: Address location() throws RemoteException; ...};

returns a copy of the address!

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Exception

• Pre-Defined Exception RemoteException• Type-Specific Exceptions• Example:

class PlayerBooked extends Exception {};interface Team extends Remote { public: ... void bookGoalies(Date d) throws RemoteException, PlayerBooked; ...};

Type-specific Exception

Operation declares that it may raise it

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JAVA (RMI) Architecture

ServerClient

Stub RegistryInterfaces

Skeleton ActivationInterfaces

RMI Runtime (rmid,rmiregistry)

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Activation in Java

Client Host

StubFaultingReferenceLiveref

Host www.bvb.de

Activa-tion ID

ActivatorActivation Descriptors:ActGroup ClassName URL InitAG1 Team www.bvb.de/…AG2 Player www.bvb.de/…AG2 Player www.bvb.de/…AG2 Player www.bvb.de/…

Java VM1 Java VM2

AG1 AG2

1: activate

2: create objectin VM

3: passobject ref

4: updatelive ref

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Key Points

• CORBA, COM and RMI – enable objects to request operation execution from

server objects on remote hosts– identify server objects by object references– distinguish between interface and implementation– treat attributes as operations– provide mechanisms to deal with failures– have statically typed object models – compile stubs from their IDLs– support on-demand activation