Chapter 4 The world wide web Learning

Chapter 4 The world wide web

Learning outcomes ¢ ¢ ¢ Explain in general terms how web documents are transferred across the Internet and What processes are triggered when you click on hyperlink Code web pages using HTML and XHTML using style sheets. Explain why it is advisable to use XHTML rather than HTML Describe some technologies available for dynamic web pages

Essential Reading ¢ ¢ ¢ Joe Casad, Teach yourself TCP/IP, Ch. 17 William Buchanan, Mastering The Internet, Ch. 6 -8 Introductory materials on HTML & XHTML either a text book such as l l l John Shelly, HTML AND CSS explained, or http: /www. web. Monkey. com http: //www. w 3 schools. com

Additional reading ¢ ¢ ¢ William Buchanan, Mastering The Internet, Ch. 9 -10 Andrew Tanenbaum, Computer Networks, Ch. 7. 3 Douglas Comer, Computer Netwoks and Networking, ch. 32 -33 Chuck Masciano and Bill Kennedy, HTML and XHTML the definitive guide, for reference http: //www. pcnetworkadvisor. com Mike Lewis, “Understanding Javascript”, June. Jully 2000

How the web works ¢ The client-server model l Client and server operate on machines which are able to communicate through a network l The server waits for requests from a clients l Server receives a requests from a client • Performs a the requested work • Or lookup the requested data • And send a response to the client l l Servers: file servers, web servers, name servers Clients: browsers, email clients

url format ¢ <scheme>: //<server-domain-name>/<pathmane> l <scheme> which protocol to use • http: in general • file: which tells the client document is in a local machine • ftp: file transfer protocol l <server-domain-name> identifies the server system • i. e. www. doc. gold. ac. uk l ¢ <pathname> tells the server where to find the file http: //doc. gold. ac. uk/~username/index. html

Web browsers and servers ¢ A browser: is a program that can retrieve files from the world wide web and render text, images, or sounds encoded in the files. l ¢ i. e. IE, Nescape, Mozilla A web server: is an application which waits for client requests, fetches requested documents from disk and transmits them the client. l i. e Apache

What happened when you click on hyperlink? ¢ ¢ ¢ Determine URL and extract domaine name. Use the name server to get IP address (DNS) Make a TCP connect to port 80 And send a request for a web page once the server has accepted to connection. The server send the file and releases the TCP connection The client displays the document.

Other possibilities ¢ ¢ The steps in the previous slide are for displaying a static web page from a remote machine. Other possibilities are: l Page is loaded from a local system • no tcp connection • url begin with file: //. . . l The page is dynamically generated by a client-side script • No tcp connection l The page is dynamically generated by a server-side script: l The server may carry out other functions • Secure server • Check user’s identity if they are authorised to access a particular resources

Stateless connection ¢ ¢ ¢ Both client and server release TCP connection after a page has been transferred. HTTP 1. 0 is stateless l Connections are not persistent l There is no indication to the server whether new transactions involve the same client HTTP 1. 1 is persistent l By keeping track of the client IP addresses l However, there is no way of identifying a repeated visits to the site by the same user. l Futhermore, ISPs reallocate IP addresses to dial-up customers as new user dial in.

Cookies ¢ ¢ Request the browser to store a small data file (cookie) on the users hard disk. Which can serve to identify users only. For instance it could contain a key into a database on the server machine. Most browsers nowadays allow you to decide whether or not you want cookies on your machine.

Introduction to HTML

What is an HTML File? ¢ HTML stands for Hyper. Text Markup Language ¢ An HTML file is a text file containing small markup tags ¢ The markup tags tell the Web browser how to display the page ¢ An HTML file must have an htm or html file extension ¢ An HTML file can be created using a simple text editor

Internet - Services ¢ ¢ ¢ ¢ Email & MIME (Multipurpose Internet Mail Extensions) text (text/html), image, video, etc. Telnet & ssh FTP – File Transfer Protocol Gopher IRC – Internet Relay Chat Newsgroups WWW – World Wide Web HTTP (Hypertext transfer protocol) uses a Question. Answer-Scheme, i. e. a browser sends a request und gets a response from a server. Note the server does not send out anything without a request.

Markup languages ¢ Suppose we have a document containing only plain text ¢ We tag certain parts of the document to indicate what they are and how they should be formatted l l This procedure is called marking-up the document Tags are usually paired: • e. g. <title>My Memoirs</title> l l A pair of tags plus their content constitute an element Un-paired tags are called empty tags

Markup languages ¢ Physical vs Semantic markup l physical refers to appearance (style) on the page l semantic refers to structure and meaning ¢ HTML is the Hyper. Text Markup Language HTML is based on SGML (Standard Generalised Markup Language) which is more complex ¢ ¢ HTML has a fixed set of tags but is constantly evolving, but newer versions are downward compatible

Markup languages ¢ ¢ ¢ HTML places primary emphasis on structure l paragraphs, headings, lists, images, links, …. HTML places secondary emphasis on style (CSS) l fonts, colours, …. HTML does not label the meaning of the text (XML)

A basic document ¢ Every document should start with the following line <!DOCTYPE html PUBLIC “-//W 3 C//DTD HTML 4. 0 Transitional//EN”> • There are three required elements, defined by the tags <html>, <head> and <body> <html> <head> <title>My Home Page</title> </head> <body> <h 1>Welcome</h 1> </body> </html>

Basic structure elements • ¢ ¢ ¢ first and last tags The HEAD section l must come before the BODY section l contains generic information about the document Elements specified in the HEAD section can include – title, link, script, style The BODY section l contains the content of the document (text, images etc) l this content is structured by other tags

Block elements ¢ • • • ¢ • Block elements define sections of text, usually preceded by a blank line <p></p> - paragraph <h 1></h 1>. . . <h 6></h 6> - headings <pre></pre> - preserve (original format) <blockquote></blockquote> - indented text <div></div> - division l used to identify a section of the document that may be subject to special formatting (for example, using stylesheets).

Paragraphs: <p>. . . </p> l l force a break between the enclosed text and the text surrounding it the tagged region of text may be subject to special formatting <p align="center">Here is another paragraph</p> – align is an attribute of the paragraph tag – center is the value of the align attribute <p>here is a piece of text that has been placed inside a paragraph</p> <p align="center">Here is another paragraph</p>

Headings ¢ ¢ Six levels of importance <h 1>. . . <h 6> Use headings to divide document into sections <html> <head> <title>Headings</title> </head> <body> <h 2>Chapter 1</h 2> <h 3>1. Introduction</h 3> This is the introduction <h 3>2. Next section</h 3> This is the next section <h 4>2. 1 A subsection</h 4> This is a subsection </body> </html>

Element relationships ¢ ¢ ¢ The elements marked by tags form a hierarchy The root element is html (marked by <html>. . . </html>) It usually has two children: head and body l each of these are further subdivided There are rules for which elements can contain other elements l e. g. headers cannot contain headers l see http: //www. w 3. org/ for a full list of rules Elements must not overlap each other l we cannot have: <h 1>. . . <a. . >. . . </h 1>. . . </a> l we can have: <h 1>. . . <a. . >. . . </a>. . . </h 1>

Inline descriptive elements Descriptive elements affect the appearance of text depending on how the text is described • <em></em> emphasis, usually with italics • <strong></strong> strong, usually with bold • <cite></cite> citation, usually in italics • <code></code> usually results in monotype spacing <body> A <em>fascinating</em> subject that I <strong>must</strong> understand </body>

Inline explicit style elements • • • <boldface></boldface> <big></big> bigger font than surrounding text <small></small> smaller font than surrounding text <i></i> italics <s></s> strikethrough <sub></sub> subscripts <sup></sup> superscripts <span></span> delimits text for stylesheet control <div></div> delimits blocks of text for stylesheet control

Inline explicit style elements <font> attributes • face - name of font (must be installed) – "arial", "times", "verdana", "helvetica" • size - absolute size (1 -7), or relative to previous text – "2", "5", "7", "+1", "-2". . . • color - hexadecimal RGB, or a named color – "3399 dd", "blue", "red" • weight - boldness from 100, 200, . . . , 900 – "100", "300", "900" ¢ e. g. <font face="arial" size="+1" color="pink" weight="300">

Unordered lists ¢ • ¢ Unordered lists <ul>. . . </ul> <li>. . . </li> for the list elements each item has a bullet some normal text <ul> <li>apples</li> <li>oranges</li> <li>pears</li> <li>bananas</li> </ul>

Ordered lists • Ordered lists <ol>. . . </ol> <li>. . . </li> for the list elements ¢ each item has a number ¢ some normal text <ol> <li>apples</li> <li>oranges</li> <li>pears</li> <li>bananas</li> </ol>

Definition lists • • • <dl></dl> The enclosing tags <dt></dt> The definition term <dd></dd> The definition <dl> <dt>MIME</dt> <dd> Multipurpose. . . </dd> <dt>FTP</dt> <dd> File transfer. . . </dd> <dt>TCP</dt> <dd> Transmission. . . </dd> </dl>

Nested lists ¢ ¢ A list may contain another list The inner list is nested inside the outer list <body> <ol> <li>apples</li> <ul> <li>red</li> <li>green</li> </ul> <li>oranges</li> <li>pears</li> <li>bananas</li> </ol> </body>

Comments ¢ Comments are delimited by  <!– this is a comment --> ¢ Comments may span multiple lines <body> <!-this is a comment --> </body>

Horizontal lines ¢ ¢ To insert a horizontal line to divide up parts of a document we use the empty tag <hr> Attributes: align, size (in pixels), width (in pixels or percentage), noshade <body> <h 1>Chapter 1</h 1> <hr align="center" size="3" width="50%" noshade> <h 2>Introduction</h 2> </body>

Special characters ¢ Some characters such as <, >, " and & have special meanings. ¢ To prevent them being interpreted as HTML code, they must be written as follows: < > " & ¢ Blank space is normally ignored in HTML. To include a space in your document use: <body> A <em> < fascinating > </em> subject that I <strong>m u s t</strong> understand </body>

Links ¢ ¢ The link (anchor) element <a>. . . </a> provides hypertext links between 1. different documents (using a URL) 2. different parts of an individual document User selection of the link (hot spot) results in 1. retrieval and display of the designated document 2. movement to relevant part of same document <body> The Department of <a href="http: //www. doc. gold. ac. uk/index. html"> Computer Science</a> is a very. . </body>

Link with URL Example: <body> The Department of <a href="http: //www. doc. gold. ac. uk/index. html"> Science</a> is a very. . </body> ¢ ¢ The href attribute gives the URL of the target page The text between the tags is highlighted – selecting it activates the link Computer

Relative addressing ¢The previous example gave the full path name, known as the absolute address <a href="research. html">Research</a> <a href=“. /pub. html">Publications</a> <a href=". . /index. html">Computer Science home</a> • The ‘root’ directory for the link is assumed to be the directory containing the parent page of the link

Images ¢ Images are included using the empty tag <img> ¢ Example: <img src="mypicture. gif" alt="my picture"> ¢ The src attribute specifies the file containing the image absolute or relative path names can be used (see notes for links) The alt attribute specifies the text to be displayed if the image is not viewed l ¢ l some users choose not to display images (for faster download) l also used for compatibility with older browsers

Image attributes ¢ The size attributes control the size of the image <img src="cat. gif" height="60" width="90" align=“top” alt="cat"> ¢ The align attribute controls the vertical location of the image, relative to the line of text – align="top" top of image aligned with top of text – align="middle" centre of image aligned with centre of text – align="bottom" bottom of image aligned with baseline of text ¢ The align attribute also controls the horizontal location of the image, relative to the line of text – align="left" image aligned with left margin – align="right" image aligned with right margin

Links with images ¢ A link element can include an image instead of text l both images and text can be included if required <body> Enter my world of cats <a href="cats. html"><img src="cat. gif" height="60" width="60" align="middle" alt="cat"></a> </body>

Colour ¢ Colours are specified with hexadecimal numbers for the red, green and blue primary colours, preceded by a “#”. ¢ To set the background colour of a web page <body bgcolor="#994422">

Colour – RGB Model – #ff 0000 (red), – #00 ff 00 (green) – #0000 ff (blue) – #ffff 00 (yellow) –. . . – #3395 ab (a pastel blue)

Colour <body text="#994422"> ¢ To set the colour of all text on a page • In the body element, the colour of link text can be controlled with the following attributes: – link for an un-visited link – vlink for a visited link – alink for a link that is currently selected by the mouse • Example <body text="#000000" link="#0000 ff">

Colour ¢ To set the colour of an individual piece of text use the font element (or preferably stylesheets – see later) <body bgcolor="#3395 ab"> Text in quotes <font color="#ff 0000">"such as this"</font> has a different colour </body>

Colour names ¢ ¢ ¢ Netscape and Internet Explorer allow textual names for colours instead of hexadecimal This is OK provided the page is not looked at by a browser that does not support colour names For example <body bgcolor="gray" text="black" link="blue">

Background patterns Rather than a uniform color ¢ You can give the background of web page a pattern as follow: ¢ <body background="tileimage. gif">

Forms ¢ Server-based programs may return data to the client as a web page ¢ Client-side scripts can read input data l To validate the data, prior to sending to server l To use in local processing which may output web page content that is displayed on the client

Example applications ¢ Questionnaires to provide feedback on a web site ¢ e-commerce, to enter name, address, details of purchase and credit-card number l request brochures from a company l make a booking for holiday, cinema etc. l buy a book, cd, etc l obtain a map giving directions to a shop ¢ Run a database query and receive results (an important part of e-commerce)

Input types • • • text checkbox radio select textarea password button submit reset hidden file image (buttons) (options)

The method and action attributes • The method attribute specifies the way that form data is sent to the server program – GET appends the data to the URL – POST sends the data separately • The action attribute specifies a server program that processes the form data (often as a URL) <body> <form method="POST" action="comments. php"> <h 2>Tell us what you think</h 2>  </form> </body>

The input element: type="text" • The type attribute specifies the type of user input • The name attribute gives an identifier to the input data <form method="POST" action="comments. php"> <h 2>Tell us what you think</h 2> Name <input name="name" type="text" size="20"> Address <input name="address" type="text" size="30"> </form>

The input element: type="checkbox" • The name attribute is used to define a set of checkboxes • The value attribute identifies the individual checkbox • If the checked attribute is set the box is initially checked How did you hear about this web site? A friend <input type="checkbox" name=“name" value="friend"> Search engine <input type="checkbox" name=“name" value="engine">

The input element: type="radio" • Radio buttons are similar to checkboxes, but only one can be selected • To select a button by default, use the checked attribute (for one button only) How did you hear about this web site? A friend <input type="radio" name=“name" value="friend"> Search engine <input type="radio" name=“name" value="engine"> <!– etc -->

The input element: type="button" • The name attribute uniquely identifies a button • The value attribute gives a label to the button • Actions can be associated with buttons using Java. Script – see later Do you want to receive any further information: <input type="button" name="yes" value=" Yes "> <input type="button" name="no" value=" No ">

The input element: type="submit/reset" • type="submit" – clicking this button sends the form data to the program (URL) specified in the action attribute of the form • type="reset" – clicking this button clears all data entered so far Thank you <input type="submit" name="send" value="Send"> <input type="reset" name="clear" value="Clear">

The input element: type="password/file/hidden" • type="password" – similar to type="text" except that the input is echoed with asterisks (so not visible) • type="file" – provides a file dialogue box to specify a file that is sent to the server • type="hidden" – similar to text input, but the value attribute is used to specify data that is to be sent to the server. Nothing appears on the screen. – The data might be set by a server program to keep track of the details of a particular transaction.

The textarea element • Used for multi-line text input • The size of the input area is specified with the cols and rows attributes • Any text placed inside the element appears in the input area (this can be deleted). Please write your comments: <textarea name="comments" rows="5" cols="20"> put text here </textarea>

The select element • The select element provides a menu of options • An option can be selected by default using the selected attribute (otherwise the first in the list is initially selected) How do you rate this site? <select name="rating"> <option>Good <option selected>Bad <option>Ugly </select>

Tables ¢ Tables provide a means of organising the layout of data ¢A table is divided into rows and columns: these specify the cells of the table

Tables • <table> element main • <tr> table row • <th> table header • <td> table data <table border="1"> <tr> <th>Name</th> <td>A B Morgan</td> <td>D P Jones</td> </tr> <th>Course</th> <td>Fishing</td> <td>Sailing</td> </tr> <th>Year</th> <td>8</td> <td>5</td> </tr> </table>

Rows and Columns ¢ Cells can span multiple columns and multiple rows with the colspan and rowspan attributes <table border="1"> <tr> <th colspan="2">Name</th> <th>Course</th> <th>Year</th> </tr> <td>A B</td> <td>Morgan</td> <td rowspan="2">Fishing</td> <td>5</td> </tr> <td>D J</td> <td>Jones</td> <td>8</td> </tr> </table>

The align and width attributes ¢ ¢ The align attribute determines the position of the text within a cell The width attribute determines the width of the row relative to the table <table border="1" align="center"> <tr> <th colspan="2" width="60%">Name</th> <th rowspan="2">Course</th> <th rowspan="2">Year</th> </tr> <th>Last</th> <th>Init. </th> </tr> <td>Morgan</td> <td>AB</td> <td>Fishing</td> <td align="center">5</td> </tr> <!– etc -->

Table attributes • • • alignment relative to the page width in pixels or percentage of page width border - width of border (pixels) cellspacing separation between cells (pixels) cellpadding - space around data inside cell (pixels) bgcolor - background colour (inside cells) Furthermore • The <caption> element puts a title above the table

Table attributes <table border="3" align="center" cellspacing="6" cellpadding="6" bgcolor="cyan"> <caption> <h 2>Course Data</h 2> </caption> <tr> <th>Name</th> <th>Course</th> <th>Year</th> </tr> <td>A B Morgan</td> <td>Fishing</td> <td>5</td> </tr> <!– etc -->

Frames and Framesets ¢ A frameset partitions a web browser window so that multiple web documents can be displayed simultaneously. ¢ Example application: To maintain a permanently visible directory of links within your site, while also displaying one or more selected documents from the site.

Framesets <html> <head><title>Frames 1</title></head> <frameset cols="140, *"> <frame name="nav. F" src="navigation. html"> <frame name="main. F" src="intro. html"> </frameset> </html> ¢ The frameset element replaces the body element • frameset has attributes cols or rows, defined in terms of pixels, percentage(%) or unspecified (*) l this splits the window into two or more columns or rows

Frame attributes <frameset cols="140, *"> <frame name="nav. F" src="navigation. html"> <frame name="main. F" src="intro. html"> </frameset> ¢ The name attribute uniquely identifies the frame. It may be used as the target in an anchor (<a>) element • The src attribute specifies the web page to be placed in the frame initially (it may subsequently be overwritten)

Frame attributes <frameset cols="140, *"> <frame name="nav. F" src="navigation. html"> <frame name="main. F" src="intro. html"> </frameset> • The scrolling attribute ("auto", "yes", "no") specifies whether the frame is to have scroll bars • The frameborder attribute ("0", "1") specifies whether the frame is to have a border

navigation. html ¢ The anchor tag has a target attribute l takes the name of the frame used to display the information ¢ All anchors below are targeted to the "main. F" frame <html><head><title>Navigation Bar</title></head> <body><center> <a href="course. html" target="main. F">HTML Course</a> <a href="paragraph. html" target="main. F">Paragraphs</a> <a href="headings. html" target="main. F">Headings</a> <a href="ulists. html" target="main. F">Unordered lists</a> <a href="olists. html" target="main. F">Ordered lists</a> <a href="nlists. html" target="main. F">Nested lists</a> <a href="intro. html" target="main. F">Home</a> </center></body>

intro. html ¢ A simple document which is initially placed in the "main. F" frame ¢ This is replaced when a user clicks on a link in the "nav. F" frame <html> <head><title>Internet Computing</title></head> <body> <h 2>Welcome to the HTML Course</h 2> <p> <h 4>Please select the subject of. . . </h 4> </p> </body> </html>

Nested framesets <html> <head><title>Frames 2</title></head> <frameset cols="140, *"> <frame name="nav. F" src="navigation. html"> <frameset rows="30%, 70%"> <frame name="upper. F" src="intro. html"> <frame name="lower. F" src="course. html"> </frameset> </html>

Noframes • Some browsers cannot process frames. Alternative content should be provided using the noframes element <html> <head><title>Frames 1</title></head> <frameset cols="140, *"> <frame name="nav. F" src="navigation. html"> <frame name="main. F" src="intro. html"> </frameset> <noframes> <body> Something here for browsers not supporting frames </body> </noframes> </html>

Stylesheets ¢ One of the most important functions of HTML is its ability to separate the content and presentation of a web document ¢ Aspects of the document presentation include • positioning on the page • choice of fonts • colours and backgrounds • borders

Styles ¢ A style is a set of formatting instructions that can be applied to a piece of text. ¢ Styles can be defined l Within a single HTML tag – Inline styles l In the <head> section, and applied to the whole document – Global styles l In external files, and can be applied to any document by including the URI of the file – Stylesheets

Inline styles ¢ Every tag has a style attribute ¢ This can be assigned a style definition ¢ ¢ A style definition is a list of property-value pairs l a property is separated from its value by a colon l property-value pairs are separated by semi-colons l the list is delimited by quotation marks A property-value pair is also called a declaration ¢ Inline styles only affect the text contained in the tag <h 1 style="color: #2255 ff; border: ridge">Inline styles</h 1>

Inline styles <body> <h 1 style="color: blue; border: ridge"> Inline styles</h 1> <p style="margin-left: 10%; background: #ffffcc"> some text. . . some text </p> <body> • The heading is boxed with the text displayed in blue • The paragraph is indented by 10% (from the left) and has a cream background

Global styles ¢ A style can be defined in the head of the document using the <style> tag ¢ The style declaration is placed inside a comment so that it can be ignored by older browsers ¢ Each style rule consists of the name of an element (selector) followed by a list of property-value pairs enclosed in curly brackets <head> <title>Styles</title> <style> <!-h 1 { color: red; border: thin groove; text-align: center; } --> </style> </head> <body> <h 1>Simple styles</h 1> </body>

Example <head> <style> <!-h 1 { color: red; border: thin groove; text-align: center; } p { margin-left: 10%; border: ridge; background: #ee 8822; } --> </style> </head> <body> <h 1>Simple styles</h 1> <p>some text. . . </p> </body> • A global style applies to every instance of the corresponding element in the document

Stylesheets ¢ Styles can be declared in separate files called stylesheets. ¢ A stylesheet is linked to a web document by including the following line in the head section <link rel="Style. Sheet" type="text/css" href="URL"> • • rel specifies the type of link being used href specifies a hyperlink to the stylesheet file type specifies the MIME type of the data text/css describes the “cascading style sheets” type

Multiple stylesheets ¢ The first stylesheet is included using the <link> tag ¢ Any further stylesheets have to be imported ¢ The @import command is placed inside a comment <head> <title>Stylesheets</title> <link rel="Style. Sheet" type="text/css" href="http: //www. abc. com/mainstyles. css"> <!– @import url(http: //www. abc. com/deptstyles. css) url(mystyles. css) --> </head>

Cascading stylesheets ¢ ¢ Multiple stylesheets can be included in a document Styles defined in the first stylesheet are overridden by corresponding styles defined in the second stylesheet the stylesheets are said to cascade Example – mainstyles. css – the company's stylesheet – deptstyles. css – the department's stylesheet – mystyles. css – the user's stylesheet l ¢ ¢ If the stylesheets are included in this order, the user's style definitions will override the department styles, which in turn will override the company styles

Cascading stylesheets ¢ Different stylesheets for different media, platforms and systems – Font size in CSS does not yield sam results on different screens. On Print Media 10 pt size fonts are always the same size because the size of a pt is well defined. The conversion of pt to px (pixel) is different on Windows, Linux or Mac OS X platforms. – Browser allow to customize layout and fonts

Style rules ¢ A style rule has two parts l a selector (element name) and a set of declarations ¢ The selector associates the style rule with a HTML tag of the same name • Each declaration has two parts: – a property and a value • For readability, each declaration should be placed on a separate line selector { property: } value;

Style rules • Some properties can be given multiple values – The browser first looks for the "Book Antiqua" font – If this is not on the system, it looks for the Times font – Last resort: the browser uses the generic serif font body { background-color: lightgreen; } h 1 { color: lightgreen; background-color: blue; font-family: "Book Antiqua", Times, serif; border: thick groove #9 baab 2; }

Properties and values Text • text-decoration: none|underline|overline|line-through • text-transformation: none|capitalize|uppercase|lowercase • text-align: left|right|center|justify • text-indentation: length|percentage Example: To remove underlining on links: a: link, a: visited, a: active{text-decoration: none}

Properties and values Boxes • margin: length|percentage|auto {1, 4} • border-width: thin|thick|medium|length {1, 4} • padding: length|percentage {1, 4} • border-color: value {1, 4} • border-style: none|dotted|dashed|solid|double|groove {1, 4} • ridge: value {1, 4} • width: length|percentage|auto • height: length|auto

Properties and values Position • location: absolute|relative|fixed – absolute: relative to upper left corner of window – relative: relative to the last item – fixed: does not move when the page is scrolled • left: distance from left border of window (pixels, %) • top: distance from top border of window (pixels, %)

Classes ¢ Simple style rules change the appearance of all instances of the associated element ¢ A class is a style definition that may be applied as and when we choose l if we don't want the styles, we don't have to use them ¢ Simple classes are applied to a single type of element ¢ Anonymous classes can be applied to any type of element

Simple classes </head> <style> <!-h 1. fred { color: #eeebd 2; background-color: #d 8 a 29 b; border: thin groove #9 baab 2; } --> </style> </head> <body> <h 1 class="fred">A Simple Heading</h 1> <p>some text. . . some text</p> </body>

Anonymous classes </head> <style> <!-. fred { color: #eeebd 2; background-color: #d 8 a 29 b; border: thin groove #9 baab 2; } --> </style> </head> <body> <h 1 class="fred">A Simple Heading</h 1> <p class="fred">some text. . . some text</p> </body>

white CSS Classes…cont. TD {font-face : sans-serif; font-size : 12 pt}. even {background-color : #FFFFFF}. odd {background-color : #CCCCCC} In your HTML code for the table: ¢ you simply reference the class to invoke the style: l • • <td class=“even”>display this text with a white background </td> <td class=“odd”>and this text with a grey background </td> grey

IDs <head> <style> <!-#list 1 { color: blue; background: cyan; text-decoration: underline; border: thin groove red; } --> </style> </head> <body> <ul id="list 1"> <li>First</li> <li>Second</li> <li>Third</li> </ul> </body> • Classes specify styles for particular instances of an element • IDs specify the style of a single element • IDs allow the element to be identified by other elements on the page

<DIV> & <SPAN> are your friends <div> and <span> tags allow you define exceptions to the general rules of your body text…and they are helpful tools for document designers and web developers <div> is usually used to designate styles for block elements that should stand apart from the body text…like callout quotes. Everything inside a <div> tag takes on the <div> attributes…and you can specify classes and ids for <div> too!

Divisions and spans ¢ Rather than applying styles to an element itself, we wrap the element in l a div element (usually for block elements), or l a span element (usually for inline elements) ¢ Any required formatting can then be applied to the <div> or <span> element. ¢ Div and span elements become part of the document l In particular, each can have class and id attributes

Divisions <head> <style> <!-. myclass { color: blue; background: cyan; text-decoration: underline; border: thin groove red; } --> </style> </head> <body> <div class="myclass"> <h 2>A Simple Heading</h 2> <p>some text. . . </p> </div> </body> ¢ Styles can be applied to blocks of HTML code using div

Spans <head> <style> <!-. myclass { color: red; background: cyan; text-decoration: none; } --> </style> </head> <body> <span class="myclass"> <h 2>A Simple Heading</h 2> <p>some text. . . </p> </span> </body> ¢ spans are similar to divisions

Layers ¢ The browser maintains a stack of layers, each containing text, images etc. The browser displays layers on top of each other (in order). ¢ The <div> tag has the following attributes – z-index: the number of the layer containing the division – left and top : the location (top-left corner) of the division in pixels – width and height: the size of the division in pixels – position: absolute or relative

Layers ¢ Layers can be manipulated using Java. Script to create Dynamic HTML pages ¢ Layers can also be used to organise page content <body> <div style="z-index: 2; left: 100 px; top: 50 px; position: absolute; background-color: red; font-size: 30"> <p>THIS STUFF IS ON TOP</p> </div> <div style="z-index: 1; left: 10 px; top: 10 px; position: absolute; background-color: yellow; font-size: 56"> <p>BACKGROUND STUFF</p></div> </body>

Summary By now you should be able to use: Tables ¢ Frames ¢ Stylesheet – CSS ¢ l Inline style l Embedded style l External style

Typical exam question explain why is it important to separate the content from the style. ¢ what is CSS? ¢ State three ways in which styles can be used. And explain the advantages and disadvantages of each one. ¢

Next Look at the disadvantages of html ¢ XML ¢ l Well formed vs valid xml document XHTML vs HTML ¢ DHTML ¢

Useful sites http: //www. w 3 schools. com/ ¢ http: //www. w 3 schools. com/html ¢ http: //www. w 3 schools. com/css ¢