Objektorienteret Netværkskommunikation (ITONK1) CORBA Introduction

Slide 2 of 24 © Ingeniørhøjskolen i Århus Outline CORBA (part one) –Introduction & Background –Architecture –Session & Presentation layer GIOP / IIOP / CDR –CORBA Interface Definition Language – IDL –Language mappings –CORBA development steps

Slide 3 of 24 © Ingeniørhøjskolen i Århus Who is the OMG? OMG: Object Management Group – Non-profit organization 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 –UML 1.1 nov > 1.5 (2004)

Slide 4 of 24 © Ingeniørhøjskolen i Århus Goal of CORBA CORBA: Common Object Request Broker Architecture 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 –But not much Microsoft support Problem with CORBA –Considered too complex by many

Slide 5 of 24 © Ingeniørhøjskolen i Århus The specifications CORBA is a collection of specifications rba_spec_catalog.htmhttp:// rba_spec_catalog.htm –Common Object Request Broker Architecture (CORBA/IIOP) (3.0.2) –CORBA Component Model (3.0) –Minimum CORBA (1.0) –Real-Time CORBA (Dynamic Scheduling) (2.0) –Real-Time CORBA (Static Scheduling) (1.1) –Many others –Realted to UML UML Profile for CORBA (1.0)

Slide 6 of 24 © Ingeniørhøjskolen i Århus Application Objects CORBA Facilities CORBA Services (mandatory) Domain Interfaces Object Management Architecture (OMA) Object Request Broker

Slide 7 of 24 © Ingeniørhøjskolen i Århus CORBA Architecture1 There are many different vendors and ORB types Many of which do not interoperate Must check specification 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

Slide 8 of 24 © Ingeniørhøjskolen i Århus One standardised interface One interface per object operation ORB-dependent interface One interface per object adapter Dynamic Invocation Client Stubs ORB Interface Implementation Skeletons Client Object Implementation ORB Core Object Adapter CORBA Architecture 2

Slide 9 of 24 © Ingeniørhøjskolen i Århus CORBA 2.0 Applications GIOP ESIOP IIOPDOETalk DCE-CIOP Mandatory: provides "out of the box" interoperability Interoperability Protocols Environment Specific..

Slide 10 of 24 © Ingeniørhøjskolen i Århus 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

Slide 11 of 24 © Ingeniørhøjskolen i Århus 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

Slide 12 of 24 © Ingeniørhøjskolen i Århus 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

Slide 13 of 24 © Ingeniørhøjskolen i Århus Heterogeneous OO Network CORBA C++ Client App.3 CORBA C# Client App.2 CORBA Java Client App.1 TCP/IP Network CORBA Cobol Database Server DB “Object Wrapping of non OO application” Different ORB’s from different vendors, on different operating systems – and written in different languages = Heterogenity

Slide 14 of 24 © Ingeniørhøjskolen i Århus IDL Common Object Model Smalltalk Cobol Java Ada-95 C++ C C CORBA Programming Language Bindings.NET Janeva / Middcor (C#)

Slide 15 of 24 © Ingeniørhøjskolen i Århus 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

Slide 16 of 24 © Ingeniørhøjskolen i Århus Example UML to IDL mapping Player -name:string -Number:int +book() Team -name:string +bookGoalies() plays in transfer(p:Player) Club -noOfMembers:int -location:Address has 1 * uses Organization #name:string coaches 1..* Trainer -name:string 11..* +train() works for

Slide 17 of 24 © Ingeniørhøjskolen i Århus Constructed types CORBA Object Model: Types typedef struct Address { string street; string postcode; string city; }; typedef sequence AddressList; interface Team {... }; Atomic types Object type

Slide 18 of 24 © Ingeniørhøjskolen i Århus 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

Slide 19 of 24 © Ingeniørhøjskolen i Århus CORBA Object Model: Attributes interface Player; typedef sequence PlayerList; interface Trainer; typedef sequence TrainerList; interface Team { readonly attribute string name; attribute TrainerList coached_by; attribute Club belongs_to; attribute PlayerList players;... }; Attribute typeAttribute name changeable Clients cannot change value

Slide 20 of 24 © Ingeniørhøjskolen i Århus CORBA Object Model: Operations interface Team {... void bookGoalies(in Date d); string print(); }; Parameter list Parameter kind Parameter type Parameter name Operation name used in requests Return types

Slide 21 of 24 © Ingeniørhøjskolen i Århus CORBA Object Model: Exceptions Generic Exceptions (e.g. network down, invalid object reference, out of memory) Type-specific Exceptions exception PlayerBooked{sequence free;}; interface Team { void bookGoalies(in Date d) raises(PlayerBooked); }; Exception data Operations declare exceptions they raise Exception name

Slide 22 of 24 © Ingeniørhøjskolen i Århus 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

Slide 23 of 24 © Ingeniørhøjskolen i Århus Interface Definition Design Server Stub Generation Client Stub Generation Server Coding Client Coding Server Registration Development Steps – CORBA vs RMI & SOAP SOAP: WSDL Java2WSDL WSDL2JAVA AXIS SOAP RMI: rmic RMI: JAVA J2SE JDK Start with Server Interface Coding: JAVA Start with Server Interface Coding: JAVA rmiregistry CORBA CORBA: IDL ORB RMI: JAVA interface C++, Java …

Slide 24 of 24 © Ingeniørhøjskolen i Århus C++ Compiler, Linker Server Client.cc Server.cc C++ Compiler, Linker Client Team.idl included in generates reads IDL-Compiler Teamcl.hh Teamcl.cc Teamsv.cc Teamsv.hh CORBA Client and Server Implementation