Page 146 - DCAP601_SIMULATION_AND_MODELING

Simulation and Modelling

Notes The chief dispute in favour of the network model, in comparison to the hierarchic model, was
that it allowed a more natural modeling of relationships between entities. Although the model
was widely implemented and used, it botched to become dominant for two main reasons.
Firstly, IBM chose to stick to the hierarchical model with semi-network extensions in their
established products such as IMS and DL/I. Secondly, it was ultimately displaced by the relational
model, which offered a higher-level, more declarative interface. Until the early 1980s the
performance benefits of the low-level navigational interfaces offered by hierarchical and network
databases were persuasive for many large-scale applications, but as hardware became faster, the
extra productivity and flexibility of the relational model led to the gradual obsolescence of the
network model in corporate enterprise usage.

9.1 Network Model of a Project

Input and Output Controllers

Network input controllers are responsible for relaying data to the proper nodes for processing.
Since it does not process the data, only relays it, there are only two requirements for an input
controller.
1. One or more input socket
2. An equal number of output paths

Output controllers function exactly the same way as input controllers, but in reverse. They both
are designed to make networks more portable. A network can have more than one input
controller and more than one output controller.
Figure 9.1: Input Output Controllers

How to Chat with Networks?

Ultimately the network user will want to communicate using characters and symbols. To
accomplish this, some kind of character set must be used. One could use ASCII, however all 8 bits
are not necessary for this purpose. ISO developed a fairly unknown 6 bit character set. It provides
English communication using the lowest number of bits possible.

140 LOVELY PROFESSIONAL UNIVERSITY