Distributed Data Processing. Topic 3. Outline. Data Processing Network Architecture for DDP Tiered Network Architecture Circuits. Data Processing. Centralized data processing Computer, data, control, staff and processing are centralized Distributed data processing (DDP)
The work done by any application program can be divided into four general functions:
“Students list” link in course homepage:
Data Access Logic
From a viewpoint of distributed application system, there are three fundamental network architectures:
The very first data communications networks were host-based, with the host computer performing all four functions. The clients enabled users to send and receive messages to and from the host computer.
This very simple architecture often works very well. Application software is developed and stored on one computer and all data are on the same computer.
In the late 1980s, there was an explosion in the use of microcomputers and microcomputer-based local area networks.
Part of this expansion was fueled by a number of low-cost, highly popular applications such as word processors, spreadsheets, and presentation graphics programs.
With client-based architectures, the clients are microcomputers on a local area network, and the host computer is a server on the same network.
This simple architecture often works well. However, as the demands for more and more network applications grow, the network circuits can become overloaded.
Example: Novell NetWare 3.12
More organizations today are moving to client-server architectures.
Client-Server attempts to balance the processing between the client and the server by having both do some of the processing.
Client-server architectures have some important benefits compared to host-based architectures.
Client-server architectures also have some critical limitations, the most important of which is their complexity.
Even updating the network with a new version of the software is more complicated too.
Much of the debate between host- and client-server networks has centered on cost. Microcomputer hardware is more than 1000 times cheaper than mainframe hardware for the same amount of computing power.
Client-server networks enable software and hardware from different vendors to be used together. Unfortunately, they have few standards. One solution is middleware, software that sits between the application software on both the client and the server.
There are dozens of standards for middleware, each of which is supported by different vendors, and each of which provides different functions.
Middleware does two things:
1. It provides a standard way of communicating that can translate between software from different vendors.
2. It manages the message transfer from clients to servers so that the clients need not know the specific server that contains the application’s data.
Examples of middleware:
Open DataBase Connectivity
Cold Fusion + ODBC + Any DBMS
JDBC is Java's version of the DBI module in Perl 5.
Two-tiered client-server architecture
Three-tiered client-server architecture
N-tiered client-server architecture
IMW’s Forum User Database Updating
SQL Server 7.0
The function of client computer
Data Access Logic
Network configuration is the basic physical layout of the network.
There are two fundamental network configurations:
Most complex computer networks have many circuits, some of each type.
Circuits can be designed to permit data to flow in one or both directions. There are three ways to transmit: