CORBA (Common Object Request Broker Architechture) Aniket Prabhune Varun Saini Balaprasuna Chennupati Lally Singh

CORBA Day1: Aniket : Introduction, OMA, ORB Core, OMG IDL, IDL Stubs and Skeletons Varun : Interface Repository, Dynamic Invocation and Dispatch (DII, DSI) Day2: Prasuna : Object Adapters, Inter-ORB protocols (IIOP/GIOP), Services (Event, Naming, Trading, Transaction) Lally: COM vs CORBA, QoS, Examples and Applications

CORBA Heterogeneous and Open Systems Engineering tradeoffs Cost Effectiveness Legacy Systems Need for integrating diverse applications within Distributed heterogeneous environments [SV97]

OMG (Object Management Group) Formed in 1989 to develop, adopt and promote standards for the development and deployment of applications in distributed heterogeneous environments. Largest software consortium in world with developers, vendors and end users on member list CORBA – Industry Standard for open distributed processing [SV97]

OMA (Object Management Architecture) Object Model and Reference Model Object Model Defines how objects distributed across a heterogeneous environment can be described Object is an encapsulated entity with a distinct immutable identity whose services can be accessed only through well defined interfaces Object References [SV97]

OMA Reference Model Characterizes the interactions between the objects Interface Categories in OMA Reference Model Object Request Broker Object Services Domain Interfaces Application Interfaces [ACP99]

OMA Object Frameworks AI DI OS AI DI ORB [ACP99] AI = Application Interface DI = Domain Interface OS = Object Service ORB = Object Request Broker

Features of CORBA: ORB Core OMG Interface Definition Language Language Mappings Stubs and Skeletons Interface Repository Dynamic Invocation and Dispatch Object Adapters Inter-ORB protocols Services [SV97]

Relation between features: Static Stub Multiple OAsSame for all applications IDL Dependant Client ApplicationServer Application Client ORB Core Server ORB Core Sktn DII DSI ORB Interface ORB Interface OA n/w [ACP99]

ORB Core Deliver request to target object Return response to the clients Transparent Client/Object Communication Object Location Object implementation Object Execution State Object communication mechanism [SV97]

IDL (Interface Definition Language) Interfaces are defined in the OMG IDL Language-Independent declarative language eg: // OMG IDL interface Factory { Object create(); }; [SV97]

IDL Includes Built-in Types: long, short, float, double, char, boolean, octet, enum, etc Constructed Types: struct, union Template Types: string, sequence, fixed point decimal Interface Inheritance: Open-Closed Principle Object Interface [SV97]

Language Mappings Determines how the OMG IDL features are mapped to the facilities of a given programming language e.g.: OMG IDL TypeC++ Mapping long, short float,double booleanbool char struct unionclass sequenceclass.... [SV97]

Stubs and Skeletons IDL interface Stub Compiler Stubs (Client Side) Skeletons (Server Side) Fixed for a given language and interface Hide the ORB from application programmer [NE95]

Marshalling & Unmarshalling eg: Acct -> List(); client target object stub skeleton client ORB server ORB program language request marshalling n/w buffer unmarshalling operation invocation [SV97] [NE95]

Design Patterns (Stubs and Skeletons) Connect programming Language world to the underlying ORB transparently Stub adapts function call style of its language mapping to the request invocation mechanism of the ORB Skeleton adapts request dispatching mechanism of the ORB to the upcall method form expected by the object implementation Form of Adapter and Proxy patterns Proxy: Provide a surrogate or placeholder for another object to control access to it Adapter: Convert the interface of class to another interface clients expect [SV97][DP95]

References: [SV97] Vinoski, S., CORBA: Integrating Diverse Applications Within Distributed Heterogeneous Environments IEEE Communications Magazine, Vol. 35, No. 2, February 1997 [NE95] Edwards, N., CORBA: An Industrial Approach to Open Distributed Computing [ACP99] Henning, M., Vinoski, S., Advanced CORBA Programming with C++, Addison Wesley, [DP95] Gamma Erich., Helm Richard, Johnson Ralph, Vlissides, John, Design Patterns: Elements of Reusable Object-Oriented Software,Addison Wesley, 1995.