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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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6.1 Further reading

There is not a lot published on distributed development paradigms. The book by Coulouris et al. [2] indirectly introduces some of the paradigms introduced in this unit. Lynch's book [3] on distributed algorithms is full of algorithms which are message passing based. The book by Patzer and 14 others [4] is a good practical introduction to many of the technologies detailed in this unit. One of the few current books on JavaSpaces has been written by Freeman et al. [1].


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4.1 Introduction

Many of you will already be familiar with event processing if you have developed visual interfaces with the later versions of Java. Developing such an interface consists of a number of steps:

  • A visual object such as a button is placed in a container such as an applet or a object.
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3.1 Distributed objects technology

This technology virtually hides the network from the designer and programmer. A distributed object is an object which is resident on one computer and for which methods can be invoked associated with code resident on other computers. A good distributed objects technology should totally hide the underlying communication details from the programmer, for example when a programmer wants to invoke the method Author(s): The Open University

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2.2 Fixed and adaptive protocols

The protocol described above for a simple naming service is an example of a fixed protocol. This is a protocol whose vocabulary is fixed: it is embedded in the client and server's code and data and does not change. An adaptive protocol is one where the protocol changes. A fixed protocol could change over a period of time because the functionality provided by a server changes. However, this change will be over months or years rather than over seconds.

There are some instances wher
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Introduction

In this unit I look at a number of different programming and design styles associated with distributed system development. The unit first examines message passing and the role of protocols – both fixed and adaptive protocols. Two styles of message passing are also examined: synchronous and asynchronous message passing. The next part of the unit introduces distributed object technology. Event-based development relies on listener objects listening to events which are propagated along a bus; t
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8 Further reading

There are a large number of books that have been written on e-commerce, many of which are of varying quality. I have found three useful. The first is by Kalakota and Whinstone (1997). It is an excellent introduction to both the technologies and applications involved in electronic commerce. Kalakota has also written a book on electronic commerce which avoids many of the clichés and which concentrates on unglamorous areas such as supply chain automation (Kalakota, 1999) . If you ignore the jar
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7.2.15 E-learning

This term is used to describe companies or organisations who offer educational courses via the web. The quality and features found in sites which can be described by this business model can vary. At its simplest such sites offer students the ability to download conventional texts. More complex instantiations of the model offer the students facilities to read individual lessons, try out online multiple choice questions and experience simulations relevant to the topic being taught.


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