Information on the web

Liz Bennett and Jon Rosewell

Unit summary

In this unit, the emphasis has been on devices communicating with each other in networks. You were introduced to some general principles about signals and networks, and the differences between wired and wireless networks. You met some of the network technologies in common use (Ethernet, WiFi and Bluetooth), before looking more closely at specific applications (smart homes, RFID systems) for networked devices. But we have barely had time to scratch the surface of what these technologies offer
Author(s): The Open University

6.9 The personalised home

In the extract from The Road Ahead, quoted at the beginning of this section, Gates makes reference to ‘an electronic pin to clip to your clothes’. This pin appears to have the ability to communicate to the network so that its wearer can be identified and located. The information can then be used to provide a personal environment for the wearer. The next section introduces you to a technology that can provide the kind of pin that Gates refers to.

6.5 Smart home networks

Some devices in a smart home may need to communicate information about the environment (for example, information about light, heat, humidity, sound, movement, water levels, etc.). They may also need to communicate to:

• give information about their state (for example, activated, deactivated, faulty);

• give temporal information (for example clock time, lapsed time, delays);

• instruct, interrogate or acknowledge another dev
  Author(s): The Open University
  

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2.8 Attenuation and distortion

As a signal travels from one device to another it has two problems to overcome. The first is that it gets weaker the further it travels, because some of its energy is absorbed by the transmission medium. This effect is known as attenuation. The extent of attenuation depends on the distance it has to travel and on the type of medium it is travelling through. An amplifier can be used to boost the signal power at the transmitter and receiver, and if necessary at various points in the tran
Author(s): The Open University

5.1 The personal computer

Over the following screens you will look at three different examples of computers: a PC, which is obviously a computer, and a set of electronic kitchen scales and a digital camera, which are not so obviously computers. You will find that all three of these examples match with the functional block diagram of a computer given in Author(s): The Open University

4.2 Representing data

But if all the data and computer instructions within a computer are represented by 1s and 0s, how can this limited set of conditions be used to represent, for instance, every letter of the alphabet that might be typed into a computer from a keyboard? Activity 4 showed that there are four possible combinations
Author(s): The Open University

2.2 Memory

You should now be beginning to build up a picture of what a computer is: you know it needs input and output devices to communicate with the world outside and a processor to carry out the instructions that are programmed into it. But where are these instructions stored within the computer? The answer is that they are stored within what is called the computer's main memory, along with any data needed to carry them out.

However, the main memory in computers like PCs is much too smal
Author(s): The Open University

1 Bringing the news on the back of a horse

We seem to be surrounded by ‘news’ these days, but it was not always like that. In Shakespeare's Henry IV Part 2, Falstaff hears the news that his former friend and drinking partner, Prince Hal, is now King Henry V, following the death of Henry IV. It is a comic scene set in Gloucestershire, 200 km from the royal court in London, and it is clear that before the messenger (called Pistol) arrived on horseback Falstaff did not even know that Henry IV had died.

It would not be li
Author(s): The Open University

Learning outcomes

This is what you should have achieved when you have completed your study of this unit:

• have developed your skills in taking notes;

• have developed your skills in evaluating Web-based resources;

• be able to recognise different learning styles;

• have developed an awareness of ethical issues involved in online communication.

Learning outcomes

By the time you have completed this unit you should:

• know the meaning of all the terms highlighted in the text;

• understand the concept of the ‘network society’;

• have an awareness of how ICTs impact on your everyday life.

7.1 The advantages of reuseability

Reuse is the process of building new software from existing software assets, rather than starting from scratch. Reuse is an important factor in building flexible products that can be changed quickly in response to changes in requirements.

One of the advantages claimed of object technology is that it encourages a disciplined approach that facilitates reuse. Encapsulation encourages better designs that can be reused in a more reliable way, as there is exact knowledge of which oper
Author(s): The Open University

6.7 Modelling with objects

Object-oriented software development is very much focused on representing the world of the problem domain as a set of interacting objects. If the classes of the objects are chosen to correspond to natural categories of things in the world, such as customer invoice, payment, bill, there will be a structural similarity between the world and the software. This can lead to good traceability from requirements through to code.

Domain, analysis and design are the three modelling perspectives t
Author(s): The Open University

6.3 Networks of objects

No serious program consists of a single object. Instead there will be a network of objects, which collaborate to achieve the functionality of the whole system. Figure 4 shows a network of objects representing a hotel, some guests and some rooms. This sort of diagram is called an object diagram or a snaps
Author(s): The Open University

4 Emergent approaches to software development

Iterative and incremental methods have been widely adopted in software development. Nowadays, high competitiveness, reduced time-to-market and pressure to develop flexible enterprise software together with the rapid change of technology have led to the emergence of new approaches to building, deploying and maintaining software. At the time of writing (2005), several new approaches to software development have been established that may become significant during the lifetime of this course. The
Author(s): The Open University

References

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
Author(s): The Open University

4.1 What is a data flow diagram?

A data flow diagram (DFD) is a graphical description of the ebb and flow of data in a given context. A DFD allows you to identify the transformations that take place on data as it moves from input to output in the system. (DFDs pre-date UML diagrams, but still have a complementary role to play in describing systems.)

The Case Study below provides an example of a DFD used to describe the Open University's eTMA system (electronic Tutor Marked Assignment system). It uses the
Author(s): The Open University

3.1 Making consistent models

It would be preferable to have a consistent way of representing the different models that one might want to construct. The notion of a modelling language allows the developer to make useful connections between different models. For the most part, models are represented diagrammatically. There are two aspects of a diagram-based modelling language that you should be aware of:

• a set of rules that defines what symbols can be used on a particular type of di
  Author(s): The Open University
  

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