Characterization of distributed systems

We define a distributed system as a collection of autonomous computers linked by a network, with software designed to produce an integrated computing facility.

What others think about distributed systems

• a distributed system is one that stops you from getting any work done whenever a machine you ve never even heard of crashes (Leslie Lamport)
• A distributed system is a collection of autonomous computers linked by a network, with software designed to produce an integrated computing facility (Brazier) [6]

The characteristics of distributed systems are:

• resource sharing
• openness
• concurrency
• scalability
• redundancy
• modularity
• integration

Object oriented programming is usually used to program distributed systems. But it is very important to understand the equation below:

object oriented distributed systems $\not=$ objects + some form of distribution

CORBA, DCOM, RMI and JINI are acronyms that you have probably heard about. You will learn more about these in this course. You should not conclude that simply combining already existing OO-Modules with for example CORBA would be sufficient to build a distributed system. This course is just a short introduction into a couple of tools and languages (in the field of distributed systems) that are available today.
The real challenge of distributed system is to design the architecture of a distributed system and to model the software in order to get a system that guarantees the required quality of service.

Figure 1: Centralized and distributed systems