Thursday, August 23, 2012

XML Usage


XML is used in many aspects of web development, often to simplify data storage and sharing.

XML Separates Data from HTML

If you need to display dynamic data in your HTML document, it will take a lot of work to edit the HTML each time the data changes.
With XML, data can be stored in separate XML files. This way you can concentrate on using HTML/CSS for display and layout, and be sure that changes in the underlying data will not require any changes to the HTML.
With a few lines of JavaScript code, you can read an external XML file and update the data content of your web page.

XML Simplifies Data Sharing

In the real world, computer systems and databases contain data in incompatible formats.
XML data is stored in plain text format. This provides a software- and hardware-independent way of storing data.
This makes it much easier to create data that can be shared by different applications.

XML Simplifies Data Transport

One of the most time-consuming challenges for developers is to exchange data between incompatible systems over the Internet.
Exchanging data as XML greatly reduces this complexity, since the data can be read by different incompatible applications.

XML Simplifies Platform Changes

Upgrading to new systems (hardware or software platforms), is always time consuming. Large amounts of data must be converted and incompatible data is often lost.
XML data is stored in text format. This makes it easier to expand or upgrade to new operating systems, new applications, or new browsers, without losing data.

XML Makes Your Data More Available

Different applications can access your data, not only in HTML pages, but also from XML data sources.
With XML, your data can be available to all kinds of "reading machines" (Handheld computers, voice machines, news feeds, etc), and make it more available for blind people, or people with other disabilities.

XML is Used to Create New Internet Languages

A lot of new Internet languages are created with XML.
Here are some examples:
  • XHTML 
  • WSDL for describing available web services
  • WAP and WML as markup languages for handheld devices
  • RSS languages for news feeds
  • RDF and OWL for describing resources and ontology
  • SMIL for describing multimedia for the web 

If Developers Have Sense

If they DO have sense, future applications will exchange their data in XML.
The future might give us word processors, spreadsheet applications and databases that can read each other's data in XML format, without any conversion utilities in between.

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Introduction to XML


XML was designed to transport and store data.
HTML was designed to display data.

What You Should Already Know

Before you continue you should have a basic understanding of the following:
  • HTML
  • JavaScript
If you want to study these subjects first, find the tutorials on our Home page.

What is XML?

  • XML stands for EXtensible Markup Language
  • XML is a markup language much like HTML
  • XML was designed to carry data, not to display data
  • XML tags are not predefined. You must define your own tags
  • XML is designed to be self-descriptive
  • XML is a W3C Recommendation

The Difference Between XML and HTML

XML is not a replacement for HTML.
XML and HTML were designed with different goals:
  • XML was designed to transport and store data, with focus on what data is
  • HTML was designed to display data, with focus on how data looks
HTML is about displaying information, while XML is about carrying information.

XML Does Not DO Anything

Maybe it is a little hard to understand, but XML does not DO anything. XML was created to structure, store, and transport information.
The following example is a note to Tove, from Jani, stored as XML:
<note>
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!</body>
</note>
The note above is quite self descriptive. It has sender and receiver information, it also has a heading and a message body.
But still, this XML document does not DO anything. It is just information wrapped in tags. Someone must write a piece of software to send, receive or display it.

With XML You Invent Your Own Tags

The tags in the example above (like <to> and <from>) are not defined in any XML standard. These tags are "invented" by the author of the XML document.
That is because the XML language has no predefined tags.
The tags used in HTML are predefined. HTML documents can only use tags defined in the HTML standard (like <p>, <h1>, etc.).
XML allows the author to define his/her own tags and his/her own document structure.

XML is Not a Replacement for HTML

XML is a complement to HTML.
It is important to understand that XML is not a replacement for HTML. In most web applications, XML is used to transport data, while HTML is used to format and display the data.
My best description of XML is this:
XML is a software- and hardware-independent tool for carrying information.

XML is a W3C Recommendation

XML became a W3C Recommendation on February 10, 1998.
To read more about the XML activities at W3C, please read our W3C Tutorial.

XML is Everywhere

XML is now as important for the Web as HTML was to the foundation of the Web.
XML is the most common tool for data transmissions between all sorts of applications.


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XML Tutorial


XML stands for eXtensible Markup Language.
XML is designed to transport and store data.
XML is important to know, and very easy to learn.


XML Document Example

<?xml version="1.0"?>
<note>
    <to>Tove</to>
    <from>Jani</from>
    <heading>Reminder</heading>
    <body>Don't forget me this weekend!</body>
</note>

XML Examples


Learn by examples! With our editor, you can edit XML and click on a test button to view the result.

XML Quiz Test


Test your XML skills at W3Schools!
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Tuesday, August 21, 2012

CSS Legal Color Values


CSS Colors

Colors in CSS can be specified by the following methods:
  • Hexadecimal colors
  • RGB colors
  • RGBA colors
  • HSL colors
  • HSLA colors
  • Predefined/Cross-browser color names

Hexadecimal Colors

Hexadecimal color values are supported in all major browsers.
A hexadecimal color is specified with: #RRGGBB, where the RR (red), GG (green) and BB (blue) hexadecimal integers specify the components of the color. All values must be between 0 and FF.

For example, the #0000ff value is rendered as blue, because the blue component is set to its highest value (ff) and the others are set to 0.

Example

p
{
background-color:#ff0000;
}

Try it yourself »

RGB Colors

RGB color values are supported in all major browsers.
An RGB color value is specified with: rgb(red, green, blue). Each parameter (red, green, and blue) defines the intensity of the color and can be an integer between 0 and 255 or a percentage value (from 0% to 100%).
For example, the rgb(0,0,255) value is rendered as blue, because the blue parameter is set to its highest value (255) and the others are set to 0.

Also, the following values define the same color: rgb(0,0,255) and rgb(0%,0%,100%).

Example

p
{
background-color:rgb(255,0,0);
}

Try it yourself »

RGBA Colors

RGBA color values are supported in IE9+, Firefox 3+, Chrome, Safari, and in Opera 10+.

RGBA color values are an extension of RGB color values with an alpha channel - which specifies the opacity of the object.

An RGBA color value is specified with: rgba(red, green, blue, alpha). The alpha parameter is a number between 0.0 (fully transparent) and 1.0 (fully opaque).

Example

p
{
background-color:rgba(255,0,0,0.5);
}

Try it yourself »

HSL Colors

HSL color values are supported in IE9+, Firefox, Chrome, Safari, and in Opera 10+.
HSL stands for hue, saturation, and lightness - and represents a cylindrical-coordinate representation of colors.
An HSL color value is specified with: hsl(hue, saturation, lightness).
Hue is a degree on the color wheel (from 0 to 360) - 0 (or 360) is red, 120 is green, 240 is blue. 
Saturation is a percentage value; 0% means a shade of gray and 100% is the full color. Lightness is also a percentage; 0% is black, 100% is white.

Example

p
{
background-color:hsl(120,65%,75%);
}

Try it yourself »

HSLA Colors

HSLA color values are supported in IE9+, Firefox 3+, Chrome, Safari, and in Opera 10+.
HSLA color values are an extension of HSL color values with an alpha channel - which specifies the opacity of the object.
An HSLA color value is specified with: hsla(hue, saturation, lightness, alpha), where the alpha parameter defines the opacity. The alpha parameter is a number between 0.0 (fully transparent) and 1.0 (fully opaque).

Example

p
{
background-color:hsla(120,65%,75%,0.3);
}

Try it yourself »

Predefined/Cross-browser Color Names

147 color names are predefined in the HTML and CSS color specification. Look at our table ofpredefined color names.
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