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3.1 Introduction

This section starts by broadly classifying different types of network, first by the nature of the communication links used to connect devices and then by a network's geographical spread. It then examines in more detail a network which uses a cabled communication link.

A networked device is often referred to as a node so we shall use this term in the sections that follow. A node is any device (for example, computer, printer, server) connected to a network, either as an end point (
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1 1 The incredible shrinking chip

Two Scottish computer engineers with little or no physics knowledge set out to make a semiconductor transistor. This was 50 years ago, and their efforts gained them the Nobel Prize. The versatility of that transistor is now at the heart of the electronics industry. Millions of transistor switches are shrunk down into the microprocessors that are found in computers, mobile phones and almost everything else electrical.

The first transistor took years to plan and make; today more are made
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7.1 Introduction

Earlier on I indicated that in order for a processor to perform a defined function it needs to be supplied with a list of instructions called a program. In this section I shall explore this idea a little further.

Software can be split into two categories, application software and operating systems. Application software is the name given to programs which enable a computer to perform specific tasks. The program that processes the image in the digital camera is one example; a word
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6 A look to the future

So what will computers do for you next? Perhaps they will be the key to solving transport problems. Driverless cars, controlled by computers, are under development. If these ever come to fruition perhaps they could help to reduce the number of road traffic accidents by automatically reducing their speed when they come too close to another car. Or perhaps journeys could be made faster and less frustrating because cars will use communicating computers to analyse traffic density and move along t
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Introduction

There is more to computers and processors than simply PCs. In fact computers are ubiquitous in everyday life. This unit challenges how we view computers through the examples of processors in kitchen scales and digital cameras, as well as a work of art that, at heart, is a computer.

This unit is from our archive and is an adapted extract from Computers and processors (T224) which is no longer taught by The Open University. If you want to study formally with us, you may wish to explore ot
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Acknowledgements

The content acknowledged below is Proprietary (seeterms and conditions) and is used under licence. This content is made available under a Creative Commons Attribution-NonCommercial-ShareAlike 2.0 Licence

All materials included in this unit are derived from content originated at the Open University.


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6.2 Authority and the variety of information sources

Technology has massively increased the number and variety of news sources that we have access to. We still have printed books, magazines and newspapers, while digital techniques have increased the number of broadcast radio and TV channels that we can get. On the Web we have access to online versions of many of these. This allows us access to media that previously would have been inaccessible.

With traditional news sources such as these, we have some understanding of the authority that t
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5.1 Transmission of electrical signals on wires

In the discussions of newsgathering in the Taylor and Higgins papers, you saw the significance of the development of systems that allowed long-distance transmission of electronic signals. Initially transmission used metallic wires (remember Taylor's reference to the importance of the ‘lines infrastructure’ and his mention of the ‘wire picture’) and later wireless transmission (terrestrial and satellite microwave) became important. In this section I shall look at some aspects of the tr
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2.4 Comparing early sources of news

Radio and newsreels

Taylor compares the merits of radio and newsreels, as sources of news, with those of newspapers.


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2.3 Newsgathering and newspapers

Newspapers

Taylor now discusses some early information and communication technologies and the extent to which they had an impact upon newspapers.


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Introduction

This unit is from our archive and it is an adapted extract from Networked living: exploring information and communication technologies (T175) which is no longer in presentation. If you wish to study formally at The Open University, you may wish to explore the courses we offer in this curriculum area.

This unit looks at the technologies used to acquire information about
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6.9 Alternatives to the main success scenario

If a use case incorporates a scenario that is significantly different from the main success scenario, you may decide to create a new subsidiary use case. There may even be a need to create more than one subsidiary, depending on what happens in different circumstances. For example, when making a reservation in a typical hotel the receptionist would first determine whether the guest was already known to the hotel (among other advantages, this would speed up the reservation process since re-ente
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6.5 More about actors

In the hotel example, you saw two actors in the use case diagram shown in Figure 3 (reproduced below). Why is the actor Guest associated with the use case for making a reservation but not associated with the use cases for checking in and out? The answer comes from an understanding of what happens when someone, a guest, arrives at a hotel. Hotels are service oriented. That is to say, they offer certain services to their guests with the intention of earning money for the business. A hote
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6.4 Scenarios

The purpose of a use case is to meet the goal of its associated actor(s), such as a guest making a reservation with a hotel. This implies that a use case should include everything that must be done to meet that goal. For example, if it is necessary to check the availability of rooms in the hotel for the desired length of stay before accepting a reservation, then we expect the use case to contain that check. In general, a use case contains a narrative about the flow of events that specifies a
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6.3 Describing use cases

To understand the work, you need a good idea of what each use case means. To get a feel for what this might entail, look again at Figure 3 (reproduced below) which shows a simple use case model for a hotel chain reservation system. Note that Figure 3 is not intended to be an exhaustive model of the hotel domain; the scope of the problem to be solved is confined to reservations and the processes of checking in and out.


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6.2 Actors

Iteration is a natural part of the modelling process. It does not matter whether you start by looking for the actors or the use cases. We have chosen to begin with the actors, since it is a way of expressing the system boundary implicitly and identifying the different views that need to be taken into account. In practice, you are likely to find that the actors are to be found in the roles that people play as employees in the problem domain, such as the hotel's receptionist or manager.

A
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6.1 Use case modelling

In this section, we take a closer look at use case modelling, and show you how it can be used to model the requirements for a product that includes the development of a software application or, simply, a system. Use case models act as a discussion tool between the requirements analyst and stakeholders, and offer a common language for agreeing the functions of a proposed system. In this discussion, we shall use the Unified Modelling Language (UML) notation (diagrams) for use cases to re
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5.1 More information about modelling techniques

The four remaining diagramming techniques are described in separate sections below, which you should now study:

Diagramming Technique Section
Use case modelling Use Cases and Activity Diagrams
Activity diagrams Use Cases and Activity Diagrams
Entity–
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Acknowledgements

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Grateful acknowledgement is made to the following for permission to reproduce material:

Ince, D. Developing Internet Applica
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References

[1] E. Freeman, S. Hupfer and A.K. Arnald, JavaSpaces Principles, Patterns and Practice. Reading, MA: Addison-Wesley, 1999.
[2] G. Coulouris, J. Dollimore and T. Kindberg, Distributed Systems Concepts and Design. Harlow: Addison-Wesley, 2001.
[3] N. Lynch, Distributed Algorithms. New York: Morgan Kauffman, 1996.
[4
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