Take your teaching online
In this free course, Take your teaching online, you will gain  knowledge fundamental to delivering effective teaching online. You will hear about the experiences of real educators, be introduced to cutting edge research, and understand the ideas and tools that shape how we teach and learn online. You will also learn useful methods that will guide you to test out these new ideas in your own practice. Author(s): Creator not set

After studying this section you should be able to do the following.

• Recognise and use the terminology: function, signature, domain, semantics, input set, output set, precondition, postcondition.

• Suggest appropriate signatures and preconditions for functions corresponding to a variety of processes on numbers, characters and sequences, including those with more than one input and those that return a Boolean value.

• For
Author(s): The Open University

Many programming languages provide two functions associated with the character codes (see Table 2). We shall call these functions ASC and CHR. ASC takes a character as input, and returns the integer giving the ASCII code of the input character. CHR returns the character whose ASCII code is the input inte
Author(s): The Open University

Having looked at some forms of data, we now turn our attention to processes that can be applied to data. Each process that we consider in this section will input data of a specified form, and will result in a corresponding value. For example, one process, which we will call ASC, takes a character as input, and has as its resulting value the integer giving the ASCII code of the input character (as listed in Author(s): The Open University

Suppose that you are designing software for some application. You will be working with a programming language that enables you to communicate instructions to a computer. In this programming language, certain forms of data will already be represented electronically. These will include common forms of data, such as numbers, characters and sequences. In any particular application, you are likely also to be concerned with forms of data that are peculiar to that application. Having identified some
Author(s): The Open University

After studying this course, you should be able to:

• understand ways in which data may be stored and processed

• distinguish between different forms of data, and use notations introduced in the course to show different forms of data

• appreciate that fine details may be important when interpreting formal notation (for example, different types of brackets may be used to distinguish between different forms of data)

• interpret a given function
Author(s): The Open University

As I outlined in the previous section, peer entities in clients and servers exchange HTTP protocol data units when they wish to transfer a resource over the web. I gave very little detail about this because I wanted to focus on the general features of protocols in the application layer of the TCP/IP model. The HTTP protocol data units are transferred from the sender host to the receiver host by calling on the services of the transport layer. In the case we are considering, the transport layer
Author(s): The Open University

Applications use easy-to-remember names for hosts on the Internet, but before sending any data to a host an application in the source host must translate its name for the destination host to the numerical network address.

The Internet is divided into domains, and an authority in each domain is responsible for allocating names. However, the domains may be divided into sub-domains and the responsibility of allocating sub-domain names may be delegated to other authorities. In this way the
Author(s): The Open University

The Internet is a worldwide public internetwork, which allows computers to communicate with each other even though they may have different manufacturers and different operating systems. The origins of the Internet lie in a project of the US Defense Advanced Research Project Agency in the 1970s, where it was intended to foster communication between research institutions rather than operate for profit. However, a substantial amount of traffic carried by the Internet is now related to com
Author(s): The Open University

An internetwork is a network of networks, composed of terminals, switches and communication media. The overall objective of an internetwork is to allow communication between two (or more) networks. This simple description hides the complications that arise in real networks, in which the types of medium vary, transmission errors occur, transmission links fail, switches fail or become congested, equipment is produced by different manufacturers, networks are owned and maintained by differ
Author(s): The Open University

They are neither finite quantities, or quantities infinitely small, nor yet nothing. May we not call them the ghosts of departed quantities?

(Bishop G. Berkeley, The Analyst)

This section follows up the ideas presented in and aims to:

• define the terms analogue, discrete and digital;

• look briefly at the human perceptual system, which e
Author(s): The Open University

Suppose I take a digital photograph of myself for my website. Horrified by my wrinkled, baggy appearance, what can I do? Actually, with the right software I can do more or less anything I like: I can smooth out the wrinkles; I can restore the grey hair to its former splendour; I can even put in a background of books to give me a scholarly appearance. In fact, I can so improve the picture that if you met the real me you probably wouldn't recognise me.

â€˜Massagingâ€™ my photographic imag
Author(s): The Open University

The AND operation combines two binary words bit by bit according to the rules

• 0 AND 0 = 0

• 0 AND 1 = 0

• 1 AND 0 = 0

• 1 AND 1 = 1

In other words, only when both bits are 1 is the result 1. You may find it helpful to think of it this way: when one bit is one and the other bit is 1 the result is 1.

Author(s): The Open University

Except for third party materials and otherwise stated (see terms and conditions). This content is made available under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 Licence

Cover image:
Author(s): The Open University

The first computer block represents the checkout terminal. The processes at the checkout (receiving, storing, retrieving, manipulating and sending data to the user), are the same as I described earlier. However, the checkout terminal also sends data via the supermarket's network.

Author(s): The Open University

As each item is scanned, the checkout computer looks up its price. The running total for each customer's purchases is stored temporarily in the checkout terminal. Other data may also be stored, such as the amount of money that has been taken at that checkout during the day.

Author(s): The Open University

As I mentioned earlier, your computer has a hard disk which provides a permanent storage area for your computer's programs and the files you create. When you save files to your computer's hard disk, you are using a magnetic storage medium. Data stored in magnetic form can be changed once it has been stored, so if you run out of space you can delete some files to make room or, if you want to edit a file, you can make the necessary changes and then save it again. At the time of writing, a mediu
Author(s): The Open University

Synchronous message passing involves one entity (usually a client) in the message passing process sending a message and a second entity (usually a server) receiving it, carrying out some processing and then sending back some response which the first entity processes in some way. While the second entity is carrying out the processing the first entity pauses waiting for the response.

In asynchronous message passing each entity in the process does not have to wait for the next part
Author(s): The Open University

It might seem paradoxical to include sites which provide free products or services under the category of business models. Typical sites which come under this category include gaming sites where users can play computer games using their browser, sites which run free raffles and sites which offer free software.

Such sites do not earn any revenues from the products or services they offer; revenue is earned indirectly, for example by means of banner adverts or by receiving revenue from site
Author(s): The Open University

The World Wide Web contains millions of web pages. Many of these pages are impossible to read, even though many existing web pages will reference them: your browser will usually return with some message such as â€˜Error 404 Page not Foundâ€™ when you try to access them. Error 404 is a standard message returned by web servers when a non-existent page is accessed. It is also the telephone area code for Atlanta in the United States; you will occasionally hear technical staff referring to non-exi
Author(s): The Open University