XML

XML is a software- and hardware-independent tool for storing and transporting data.

Why Study XML?

XML plays an important role in many IT systems.

For this reason, it is important for all software developers to have a good understanding of XML.

Before you continue, you should also have a basic understanding of:

  • HTML
  • JavaScript

What is XML?

  • XML stands for EXtensible Markup Language
  • XML is a markup language much like HTML
  • XML was designed to store and transport data
  • XML was designed to be self-descriptive
  • XML is a W3C Recommendation
  • XML was designed to be both human- and machine-readable.

XML Does Not DO Anything

Maybe it is a little hard to understand, but XML does not DO anything.

This note is a note to Tove, from Jani, stored as XML:

Example 1

<?xml version="1.0" encoding="UTF-8"?>
<note>
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!</body>
</note>

 

Example 2

<?xml version="1.0" encoding="UTF-8"?>
<breakfast_menu>
<food>
<name>Belgian Waffles</name>
<price>$5.95</price>
<description>Our famous Belgian Waffles with plenty of real maple syrup</description>
<calories>650</calories>
</food>
<food>
<name>French Toast</name>
<price>$4.50</price>
<description>Thick slices made from our homemade sourdough bread</description>
<calories>600</calories>
</food>
<food>
<name>Homestyle Breakfast</name>
<price>$6.95</price>
<description>Two eggs, bacon or sausage, toast, and our ever-popular hash browns</description>
<calories>950</calories>
</food>
</breakfast_menu>

The note 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. XML is just information wrapped in tags. Someone must write a piece of software to send, receive, store, or display it:

Note

To: Tove

From: Jani

Reminder

Don't forget me this weekend!

The Difference Between XML and HTML

XML and HTML were designed with different goals:

  • XML was designed to carry data – with focus on what data is
  • HTML was designed to display data – with focus on how data looks
  • XML tags are not predefined like HTML tags are

XML Does Not Use Predefined Tags
The XML language has no predefined 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.

HTML works with predefined tags like <p>, <h1>, <table>, etc.

With XML, the author must define both the tags and the document structure.

XML is Extensible

Most XML applications will work as expected even if new data is added (or removed).

Imagine an application designed to display the original version of note.xml (<to> <from> <heading> <data>).

Then imagine a newer version of note.xml with added <date> and <hour> elements, and a removed <heading>.

The way XML is constructed, older version of the application can still work:

<note>
<date>2015-09-01</date>
<hour>08:30</hour>
<to>Tove</to>
<from>Jani</from>
<body>Don't forget me this weekend!</body>
</note>

 

XML Simplifies Things

  • It simplifies data sharing
  • It simplifies data transport
  • It simplifies platform changes
  • It simplifies data availability

Many computer systems contain data in incompatible formats. Exchanging data between incompatible systems (or upgraded systems) is a time-consuming task for web developers. Large amounts of data must be converted, and incompatible data is often lost.

XML stores data in plain text format. This provides a software- and hardware-independent way of storing, transporting, and sharing data.

XML also makes it easier to expand or upgrade to new operating systems, new applications, or new browsers, without losing data.

With XML, data can be available to all kinds of “reading machines” like people, computers, voice machines, news feeds, etc.

How Can XML be Used?

XML is used in many aspects of web development.

XML is often used to separate data from presentation.

XML Separates Data from Presentation

XML does not carry any information about how to be displayed.

The same XML data can be used in many different presentation scenarios.

Because of this, with XML, there is a full separation between data and presentation.

XML is Often a Complement to HTML

In many HTML applications, XML is used to store or transport data, while HTML is used to format and display the same data.

XML Separates Data from HTML

When displaying data in HTML, you should not have to edit the HTML file when the data changes.

With XML, the data can be stored in separate XML files.

With a few lines of JavaScript code, you can read an XML file and update the data content of any HTML page.

Books.xml

<?xml version="1.0" encoding="UTF-8"?>
<bookstore>

<book category="cooking">
<title lang="en">Everyday Italian</title>
<author>Giada De Laurentiis</author>
<year>2005</year>
<price>30.00</price>
</book>

<book category="children">
<title lang="en">Harry Potter</title>
<author>J K. Rowling</author>
<year>2005</year>
<price>29.99</price>
</book>

<book category="web">
<title lang="en">XQuery Kick Start</title>
<author>James McGovern</author>
<author>Per Bothner</author>
<author>Kurt Cagle</author>
<author>James Linn</author>
<author>Vaidyanathan Nagarajan</author>
<year>2003</year>
<price>49.99</price>
</book>

<book category="web" cover="paperback">
<title lang="en">Learning XML</title>
<author>Erik T. Ray</author>
<year>2003</year>
<price>39.95</price>
</book>

</bookstore>

 

Transaction Data

Thousands of XML formats exists, in many different industries, to describe day-to-day data transactions:

  • Stocks and Shares
  • Financial transactions
  • Medical data
  • Mathematical data
  • Scientific measurements
  • News information
  • Weather services

Example: XML News

XMLNews is a specification for exchanging news and other information.

Using a standard makes it easier for both news producers and news consumers to produce, receive, and archive any kind of news information across different hardware, software, and programming languages.

An example XMLNews document:

<?xml version="1.0" encoding="UTF-8"?>
<nitf>
<head>
<title>Colombia Earthquake</title>
</head>
<body>
<headline>
<hl1>143 Dead in Colombia Earthquake</hl1>
</headline>
<byline>
<bytag>By Jared Kotler, Associated Press Writer</bytag>
</byline>
<dateline>
<location>Bogota, Colombia</location>
<date>Monday January 25 1999 7:28 ET</date>
</dateline>
</body>
</nitf>

Example: XML Weather Service

An XML national weather service from NOAA (National Oceanic and Atmospheric Administration):

<?xml version="1.0" encoding="UTF-8"?>
<current_observation>

<credit>NOAA's National Weather Service</credit>
<credit_URL>http://weather.gov/</credit_URL>

<image>
<url>http://weather.gov/images/xml_logo.gif</url>
<title>NOAA's National Weather Service</title>
<link>http://weather.gov</link>
</image>

<location>New York/John F. Kennedy Intl Airport, NY</location>
<station_id>KJFK</station_id>
<latitude>40.66</latitude>
<longitude>-73.78</longitude>
<observation_time_rfc822>Mon, 11 Feb 2008 06:51:00 -0500 EST
</observation_time_rfc822>

<weather>A Few Clouds</weather>
<temp_f>11</temp_f>
<temp_c>-12</temp_c>
<relative_humidity>36</relative_humidity>
<wind_dir>West</wind_dir>
<wind_degrees>280</wind_degrees>
<wind_mph>18.4</wind_mph>
<wind_gust_mph>29</wind_gust_mph>
<pressure_mb>1023.6</pressure_mb>
<pressure_in>30.23</pressure_in>
<dewpoint_f>-11</dewpoint_f>
<dewpoint_c>-24</dewpoint_c>
<windchill_f>-7</windchill_f>
<windchill_c>-22</windchill_c>
<visibility_mi>10.00</visibility_mi>

<icon_url_base>http://weather.gov/weather/images/fcicons/</icon_url_base>
<icon_url_name>nfew.jpg</icon_url_name>
<disclaimer_url>http://weather.gov/disclaimer.html</disclaimer_url>
<copyright_url>http://weather.gov/disclaimer.html</copyright_url>

</current_observation>

 

Source: w3schools.com

© 2024 bhabasankar.com | All rights reserved.