[ Syllabus ] [ Teaching materials ] [ References ]

Distributed Object-Oriented Systems

Motivation:

Constant innovation in computing industry has brought large mass of sophisticated application. A set of problems has been derived from the sophistication for both developers and users. Applications are time-consuming to develop, difficult and costly to maintain. Functionality and data of one application generally are not available to other applications even if they are running on the same computer. Very often the same services provided by the operating system and the network are different. Programming models are also inconsistent. They are vary widely depending on whether the service is coming from a provider in the same address space as the client program, from a separate process on the same computer, from the operating system, or from a provider running on a separate computer across the network.

Another consequence of the increasing software complexity is the need for a new approach of developing software featured by

the object-oriented concepts to re-use existing solutions, and to facilitate new designs of more self-sufficient software components;
the client-server computing to communicate between powerful workstations and network servers;
the distributed computing to provide a single system image to users and applications and to permit use of services in a networked environment regardless of location, computer architecture, or implementation environment.

Responding to the increasing demand, a variety of distributed frameworks have been started to develop. Such frameworks facilitate the creation of collaborative distributed applications. Maybe the best-known representatives of such distributed framework is the CORBA

The Common Object Request Broker Architecture (CORBA) is structured to allow integration of a wide variety of object systems, developed by the Object Management Group (OMG).

The client is the entity that wishes to perform an operation on the object and the object implementation is the code and data that actually implements the object. The ORB (Object Request Broker) is responsible for all of the mechanisms required to find the object implementation for the request, to prepare the object implementation to receive the request, and to communicate the data making up the request. The interface the client sees is completely independent of where the object is located, what programming language it is implemented in, or any other aspect which is not reflected in the object's interface.

To make a request, the client can use the Dynamic Invocation interface (the same interface independent of the target object's interface) or an OMG Interface Definition Language (OMG IDL) stub (the specific stub depending on the interface of the target object). The client can also directly interact with the ORB for some functions.

The ORB locates the appropriate implementation code, transmits parameters and transfers control to the object implementation through an IDL skeleton or a dynamic skeleton. Skeletons are specific to the interface and the object adapter. In performing the request, the object implementation may obtain some services from the ORB through the Object Adapter. When the request is complete, control and output values are returned to the client.

ORB is not required to be implemented as a single component, but rather it is defined by its interfaces. Any ORB implementation that provides the appropriate interface is acceptable. The ORB Core is that part of the ORB that provides the basic representation of objects and communication of requests. CORBA is designed to support different object mechanisms, and it does so by structuring the ORB with components above the ORB Core, which provide interfaces that can mask the differences between ORB Cores.

Aim:

This course is intended to bring together the student's knowledge of object-oriented software development and networking and to extend it into the creation of distributed object-oriented systems. We set the objective to develop a new course to introduce CORBA both on theoretical and practical level.

Objectives:

On completion of this course student will be able to:

use Java programming language
understand the client-server computation model
understand the CORBA concepts
design and implement simple distributed applications

Approach:

The theoretical aspects of this topic will be covered in lectures to convey the fundamental issues. Practical exercises will concentrate on the use of framework and creation applications. The particular tools to be used (ORBIX, Java, etc) will be defined after evaluating experiencies are from TEMPUS partners.