CS551 - Lecture 101
CS551 Object Oriented Middleware (II) (Chap. 4 of EDO)
Yugi LeeSTB #555(816) [email protected]/~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