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Lesson 2 The history of networking
Objective Explain the Evolution from Centralized to Decentralized Computers.

Evolution from Centralized to Decentralized Computers

While the computing environment of the 1990s is characterized by widely distributed systems, this decentralized database approach is actually a relatively new phenomenon.
It is very important to understand that the client/server model does much more than distribute data across a network. One of the foremost reasons for using the client/server model is to share the processing load.

Central data, central processing, distributed data, distributed processing
Central data, central processing, distributed data, distributed processing

In the four quadrants of this graph, we see several common approaches to the distribution of Oracle data and processors:
  1. centralized data and centralized processing,
  2. centralized data and distributed processing,
  3. distributed data and centralized processing, and
  4. distributed data and distributed processing.


All systems fall somewhere within these four domains, depending on the amount of distributed processing and number of distributed databases. The Oracle solution facilitates all of them. A distributed data store is a network in which a user stores his or her information on a number of peer network nodes. The user also usually reciprocates and allows users to use his or her computer as a storage node as well. Information may or may not be accessible to other users depending on the design of the network.

Distributed databases have become an integral part of business computing in the last 10 years. The ability to maintain the integrity of data and provide accurate and timely processing of database queries and updates across multiple sites has been an important factor in enabling businesses to utilize data in a range of different locations, sometimes on a global scale. Standardization of query languages, and of the Relational and Object models has assisted the integration of different database systems to form networks of integrated data services. The difficulties of ensuring the integrity of data, that updates are timely, and that users receive a uniform rate of response no matter where on the network they are situated remain, in many circumstances, major challenges to database vendors and users.
In this unit we shall introduce the topic of distributed database systems. We shall examine a range of approaches to distributing data across networks, and examine a range of strategies for ensuring the integrity and timeliness of the data concerned. We shall look at mechanisms for enabling transactions to be performed across different machines, and the various update strategies that can be applied when data is distributed across different sites. In the next lesson, we will take a look at the evolution of network protocols.