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2.2 What are signals?

To convey data from one point to another we need to represent the data by means of a signal. We can think of a signal as a deliberate variation in some property of the medium used to convey the data. Some examples are:

  • an electrical voltage travelling along copper wires between your telephone and the local exchange;

  • pulses of light (though we might not be able to see them) in a fibre-optic cable;

  • the radio emissions t
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1.1 Getting an overview

This section starts with an article from a technical journal – the sort that is read by academics and professionals working in a related technical field. It sets the scene for some of the technologies and issues that you will be encountering later in this unit.

We're not going to ask you to read the entire article, but we would like you to get an idea of the article's contents, the kind of points the author is making, and the range of issues that it throws up. With this aim in mind, w
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Learning outcomes

When you have completed your study of this unit, you should be able to:

  • understand and use correctly terms introduced in this unit in relation to communication networks;

  • understand general principles involved in data exchange between ICT devices;

  • work with numbers expressed in scientific notation, and use the Windows calculator to perform calculations on these numbers.


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Acknowledgements

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

Grateful acknowledgement is made to the following sources for permission to reproduce material in this unit:

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2 2 Conclusion

The versatile tiny transistor is now at the heart of the electronics industry. In the video clips you have seen the history of the incredible shrinking chip, its Scottish connections, and an explanation of the physics that make chips work as well as a reconstruction of making a transistor using the crude techniques of yesteryear.


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Introduction

This unit focuses on the creation of a semiconductor transistor – a versatile tiny transistor that is now at the heart of the electronics industry. In the video clips, the history of the incredible shrinking chip, its Scottish connections and an explanation of the physics that make chips work are accompanied by a reconstruction of making a transistor using the crude techniques of yesteryear.


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Acknowledgements

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Grateful acknowledgement is made to the following sources for permission to reproduce material within this unit.

Figures

Figure 6 NanoElectronics Japan

Figure 30 The Cottingley Fairies © Science and Society Picture Library

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2.6 New media

From film to videotape

Taylor now describes the era when film was replaced with analogue electrical video.


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6.8 Sharing behaviour between use cases

For each use case there may be more than one scenario. In the process of requirements elicitation and specification, you may find a certain amount of common behaviour in two or more of your use cases. You may even find that an existing component can provide part or all of that common or shared behaviour. Indeed, if you do find such an existing component, this is an example of reusing requirements which is discussed more fully in MRP.

You can record the shared behaviour in
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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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1.1 Types of model

When the word model is used, you are most likely to bring to mind physical models such as those that are constructed to depict new buildings, cars or other artefacts. Such models are a precursor to actually building the artefact ‘for real’. However, our use of the word goes beyond physical models. For example, when a new house is built there will be a variety of plans produced to show different aspects of the house: its floor plan, a diagram of its location, a drawing of the front elevati
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5.2 An example

In order to complete this section I shall present a simple example. This is loosely based on one described in [1], currently one of the very few books written on JavaSpaces technology.

An object that can be stored in a space has to implement an interface . The objects that form part of the example will just
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1.8 Maintenance

Databases are one of the more enduring software engineering artefacts; it is not uncommon to find database implementations whose use can be traced back for 15 years or more. Consequently, maintenance of the database is a key issue.

Maintenance can take three main forms:

  • Operational maintenance, where the performance of the database is monitored. If it falls below some acceptable standard, then reorganisation of the database, usuall
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1.7 Testing

The aim of testing is to uncover errors in the design and implementation of the database, its structure, constraints and associated user and management support. Testing is usually considered to involve two main tasks – validation and verification. Without adequate testing users will have little confidence in their data processing.

Validation answers the question: has the right database been developed to meet the requirements? It attempts to confirm that the right database has been co
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6.1.1 The user interface

An interface to a washing machine does not need to be like the interface to a personal computer (a user interface is a display/control panel that enables the user to control a machine or interact with a program). It is specific to the task of washing laundry, which involves two things:

  1. displaying the choices that relate to washing laundry (such as type of laundry to be washed, water temperature, and spin speed);

  2. displaying some indica
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4.2.2 Using the web more effectively: gateways

A gateway on the web is a website intended to direct users to other preselected websites containing information on a particular topic. It can also refer to a computer that acts as a message router on the internet

University librarians often set up gateways for particular areas of study, although they may be set up by anyone with sufficient expertise in a topic. Gateways may be fairly general, such as a gateway site for sciences, or more specific, such as a gateway for part
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3.4.1 A computer system is the combination of:

  • the computer (with its processor and storage);

  • other equipment such as a scanner or printer,

  • the software programs that make it all work (software programs that are designed to help with some human task are often referred to as applications).


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3.1 Making sensation make sense

In the previous section you learned something about what data is, where it can be found, and how it can be used. But have you ever thought about how we get data in the first place? As human beings, we are so used to reading, writing, speaking and observing that we rarely think about the true origins of the data we commonly use with such ease. I don't intend taking you back to these origins – that would take too long. Rather, I want to describe how human beings ‘get’ data and put it into
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2.1.2 Data and information

So far, I have used two words in connection with computers: data and information. Did you see any differences in the way the two terms have been used? Let me point out one.

Data refers to discrete items, such as the price of an item on the shelf of a supermarket, or the type of product listed on a sign over a supermarket aisle. The word ‘data’ is a plural Latin word but it is generally used as a singular word in English.

In contrast, information involves linking
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Introduction

School governors need to be involved in the monitoring and evaluation of secondary schools. But what areas should you be monitoring and how can you ensure that monitoring is effective. This course will help you assess these matters and also look at the kind of evidence you should be sourcing, and how that evidence should be evaluated.

This OpenLearn course provides a sample of postgraduate study in Author(s): The Open University

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