1. ©2002-2003 G. Michael Youngblood
Introduction to CORBA
G. Michael Youngblood
Artificial Intelligence Laboratory
The University of Texas at Arlington
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2. ©2002-2003 G. Michael Youngblood
Objectives
CORBA technology introduction
CORBA terminology introduction
CORBA references introduction
CORBA IDL
CORBA Applications
CORBA Services
CORBA demonstration
Additional information
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3. CORBA Technology Overview
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CORBA
Common Object Request Broker Architecture
Specification written and maintained by the Object Management Group (OMG)
First Specification: OMA Object Management Architecture
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5. Object Management Architecture
Object: an encapsulated entity with an immutable distinct identity whose services are accessed only through well-defined interfaces.
Interface Categories: general groupings for object interfaces. Conceptually linked by an ORB.
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6. OMA: Interface Categories
Object Services: domain-independent, or horizontally oriented, interfaces used by many distributed object applications. Ex: Naming Service, Trading Service
Domain Interfaces: domain-specific, or vertically oriented, interfaces usu. Industry specific. Ex: Person Identification Service
Application Interfaces: developed specifically for a given application. Ex: your own CORBA applications
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7. OMA interface categories
Domain Interfaces
Domain Interfaces
Application Interfaces
Domain Interfaces
Domain Interfaces
Domain Interfaces
Object Request Broker
Object Services
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8. ©2002-2003 G. Michael Youngblood
CORBA Terminology
Side step..
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CORBA Terminology
CORBA Object: a “virtual” entity capable of being located by an ORB and having client requests invoked on it.
Target Object: within the context of a CORBA request invocation, it is the CORBA object that is the target of that request.
Client: an entity that invokes a request on a CORBA object,
Server: an application in which one or more CORBA objects exist.
Request: an operation invocation on a CORBA object by a client.
Object Reference: a handle used to identify, locate, and address a CORBA object.
Servant: a programming language entity that implements one or more CORBA objects.
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10. CORBA Technology Overview
Returning…
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11. OMA realized through CORBA
CORBA provides platform-independent programming interfaces and models for portable distributed object-oriented computing applications.
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CORBA major features
OMG Interface Definition Language
Language Mappings
Operation invocation and dispatch facilities (static and dynamic)
Object adapters
Inter-ORB Protocol
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CORBA Architecture
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IDL
Interface Definition Language
Sole purpose is to allow object interfaces to be defined in a manner that is independent of any particular programming language.
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Language Mappings
IDL-to-Programming Language mappings are defined.
C, C++, Java, Ada, LISP, XML, COBOL, FORTRAN, Smalltalk, Eiffel, Perl, Python, Tcl, etc.
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16. Operation Invocation and Dispatch Facilities
Static invocation and dispatch
IDL translated into language-specific stubs and skeletons that are compiled into applications.
Dynamic invocation and dispatch
Construction and dispatch of CORBA requests at run time.
Interface and types determined by outside means (e.g., Interface Repository)
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Object Adapters
Serve as glue between servants and the ORB
Fulfill 3 requirements
Create object references, which allow clients to address objects
Ensure each target object is incarnated by a servant
Takes requests dispatched by a server-side ORB and further directs them to servants incarnating each of the target objects
POA!
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Inter-ORB Protocols
ORB-to-ORB communication (even between different implementations)
GIOP (“gee-op”): General Inter-ORB Protocol
An abstract protocol that specifies transfer syntax and a standard set of message formats to allow independently developed ORBs to communicate over any connection-oriented transport.
IIOP (“eye-op”): Internet Inter-ORB Protocol
GIOP over TCP/IP
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IOR
ORB interoperability also requires standardized object reference formats.
Interoperable Object References (IOR)
Standard object reference format
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How does it work?
Request Invocation
Object Reference Semantics
Reference Acquisition
Contents of an Object Reference
References and Proxies
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21. ©2002-2003 G. Michael Youngblood
Request Invocation
When a client invokes an operation via an object reference, the ORB does the following:
Locates the target object
Activates the server application if the server is not already running
Transmits any arguments for the call to the object
Activates a servant for the object if necessary
Waits for the request to complete
Returns any out and inout parameters and the return value to the client when the call completes successfully
Returns an exception (including any data contained in the exception) to the client when the call fails
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22. Request Invocation Characteristics
The entire request invocation mechanism is completely transparent to the client, to whom it looks like an ordinary method invocation on a local object.
Request characteristics:
Location transparency
Server transparency
Language independence
Implementation independence
Architecture independence
OS independence
Protocol independence
Transport independence
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23. Object Reference Semantics
Every object reference identifies exactly one object instance
Several different references can denote the same object
References can be nil
References can dangle
Reference are opaque (the client is not allowed to look at their contents)
References are strongly typed
References support late binding
References can be persistent
References can be interoperable
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24. Reference Acquisition
Object references are the only way for a client to reach target objects.
How does a client get a server’s object reference?
Bootstrapping
Naming or Trading Service
Command-line or reading a file
Out-of-band method
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25. Contents of an Object Reference
Repository ID
Endpoint Info
Object Key
Repository ID (standardized)
Endpoint Info (standardized)
Object Key (proprietary)
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26. References and Proxies
When a reference is received by a client, the client-side run time instantiates a proxy object in the client’s address space
This proxy is an instance that supplies an interface to the target object to the client.
Client
Server
Proxy
Skeleton Instance
foo()
foo()
foo()
Object Reference
foo()
Servant
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Questions?
CORBA Technology Overview
CORBA Terminology
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CORBA References
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29. OMG’s Document Access Page
OMG Specifications
Key Specifications
Architecture and Specification (CORBA/IIOP)
IDL
Language Mappings
Services
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Good Books
The C++ Standard… Advanced CORBA Programming with C++ by Michi Henning and Steve Vinoski\
Many examples… PURE CORBA by Fintan Bolton
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Implementations
Orbacus
OmniORB
MICO
TAO (The ACE ORB)
ORBit
etc.
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Questions?
CORBA References
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33. CORBA Interface Definition Language (IDL)
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34. Interface Definiton Languge
Simple language
Mappings to most modern popular programming languages
Compiled into stub and skeleton code by an IDL compiler
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IDL Compilation
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IDL Simple Example
// description of the module AddressBook
module AddressBook {
interface Person
attribute string name;
string send (in string fromWhom); };
} ;
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IDL Data Types
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IDL Supports
Constants
Custom types
Attributes
Methods
Structures
Exceptions
Interfaces
Modules
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Questions
CORBA IDL
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CORBA Applications
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41. General CORBA Application Development
Determine your application's objects and define their interfaces in IDL
Compile your IDL definitions into C++ stubs and skeletons
Declare and implement C++ servant classes that can incarnate your CORBA objects
Write a server main program
Compile and link your server implementation files with the generated stubs and skeletons to create your server executable
Write, compile, and link your code together with generated stubs
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Examples
Coming soon…
Please hold questions until demonstration
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CORBA Services
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CORBA Services
OMG Naming Service
Basically, DNS for IORs
OMG Trading Service
Service discovery
OMG Event Service
Broadcast events
Interface Repository
Time Service
etc.
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Questions?
CORBA Services
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CORBA Demonstration
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CORBA Examples
Simple Client-Server
Advanced Client-Server
Advanced Client-Server using NameService
Advanced Client-Server using NameService invoking a Callback
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Questions?
CORBA Applications
CORBA demonstrations
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49. Additional Information
Are there any questions?
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Questions
Any other questions?
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References
Henning, Michi and Steve Vinoski. Advanced CORBA Programming with C++. Addison-Wesley: Reading, MA
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52. G. Michael Youngblood youngbld@cse.uta.edu http://tauceti.uta.edu
Thank You!
G. Michael Youngblood
7/16/2019
© G. Michael Youngblood