1. Computer Networks
Lesson 4

2. Starter
Work in pairs to complete the word search and write a definition for the words and phrases you find in the grid.

3. Objective of the Lesson
Understand how HTML works and the most common file types used over the internet.
All of you will:
Explain what HTML, PDF files and GIF files are used for.
Most of you will:
Create a simple webpage using HTML.
Describe the difference between lossy and lossless file compression.
Some of you will:
Create a more advanced web page including links to external sources.

4. Homework
Everybody should create a simple web page using HTML and it to your teacher for marking.
Some of you may also want to get the extra marks by creating a more advanced website.
This homework is due in next lesson.
Make sure you have written your homework clearly in your planner.

5. What is the Internet?
The internet is a world wide network connecting millions of networks together over the globe.
This allows us to share information easily between computers.
It has revolutionised how people search for information, communicate with each other and how businesses advertise and sell to their customers.

6. <p>This is a paragraph.</p>
HTML
HTML is a language used for creating web pages.
HTML stands for Hyper Text Markup Language
It uses tags to describe the code. These are shown in triangular brackets as shown below:
<p>This is a paragraph.</p>
This ends the code.
This starts the code.

7. Common Tags in HTML
<h1>This is a main heading</h1>
<h2>This is a sub-heading</h2>
<p>This is a paragraph.</p>
<a href=" is a link</a>
<a an </a>
<b>Bold text</b>
<i>Italic text</i>
Start a new file using Notepad and enter the text as shown above.
Save the file as Test.html.
Open it up using a web browser and see what has happened to the tags.

8. HTML HTML has become the standard language used on websites.
It is compact, very flexible and relatively easy to learn the basics.
The HTML language was designed to be an efficient way of transferring and formatting data and was designed to be able to change as new media formats were created, whilst still remaining predictable to use.

9. Who created HTML?
The standard language is decided upon by a large body of volunteers and experts called “The World Wide Web Consortium”
They oversee the progress of the HTML language and guide its development.
If you create a website using HTML then it should be readable by all browsers which understand HTML.

10. XHTML The next generation of HTML is called XHTML
XHTML is stricter in its definition of tags (you can't get away with lazy marking-up, such as missing off closing tags) but it is much more flexible.
When a computer reads any kind of document, it must follow a strict pattern or syntax, and the stricter this is, the easier the computer finds the interpretation.
Web development software such as Dreamweaver and dedicated FrontPage make writing HTML and XHTML much easier.

11. CSS
Much of the formatting of webpages can now be managed using Cascading Style Sheets (CSS).
Cascading Style Sheets is a markup- based language used for describing the formatting of a document.
A user can define their own styles for text for instance (Main Title = Bold, Large, Times New Roman and Red) and then this can be applied throughout a whole website and updated as necessary.
This saves time and effort for the developer and ensures that a website has a consistent look.

12. What Do You Know About File Types?
Work in pairs and decide what the following file types are used for:
JPEG
MPEG
PDF
GIF
MP3
PNG

13. File Types
Websites need to be as small as possible so that they do not take too long to load when a user wants to see the page.
There are several file types which are used as standard in order to make sure they can be easily read and seen by all internet browsers.
These include:
JPEG, GIF and PNG – used for image files
MPEG and MP3 – used for video and sound files
PDF – used for other file types which can be downloaded

14. Images
Most internet browsers understand GIF and JPEG image formats and most newer browsers also understand the PNG image format.
To avoid long delays while the image is downloaded over the network, you should avoid using large image files.
Generally speaking, JPEG is best for photographs, while GIF and PNG are good for graphics using flat areas of colour and lines.

15. MPEG and MP3
The Moving Picture Experts Group (MPEG) has developed a compression system used for video files.
MPEG generally produces better-quality video than other video formats, such as Video for Windows or QuickTime.
The MPEG compression system includes another system to compress sound files called MPEG Audio Layer-3 (MP3).
MP3 can compress a song to around 10% of the original file size, but still retains something close to CD quality.

16. PDF files
Portable Document Format (PDF) is an open standard file type used to exchange documents.
It was originally created by Adobe. Many people install Adobe Reader onto their PC in order to read it although it can be read by other software such as Kindle.
Nearly any type of file can be converted into a PDF file and this is a usual format in which to save files to be transmitted over the internet as the recipient can read it easily.
PDF documents are a very convenient format to send documents as they generally cannot be changed.
They print out easily and accurately without having to change the formatting.

17. File Compression
All kinds of files can be compressed so that they can be transferred quickly: audio files, video files and still images.
There are, broadly, two forms of compression:
Lossless
Lossy
Lossless compression recreates a compressed file as an identical match to its original form and is usually used for files, such as applications, that need to be reproduced exactly like the original file.
Lossy compression, on the other hand, eliminates repeated pieces of data which means that when the file is uncompressed it may have lost some of its quality.

18. Complete the Crossword
Work in pairs to complete the crossword to recap what you have learnt today.