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XML
CS 105
What is XML?• XML stands for Extensible Markup Language.• XML is a markup language like HTML.• XML was designed to describe data.• You must define your own tags.
An XML Example
<note>
<to>John</to>
<from>Merry</from>
<heading>Reminder</heading>
<body>Don’t forget to pick up the box</body>
</note>
Why XML?
• There is a huge number of websites on the web and each website posts tunes of web pages. Also the number of web sites increases day by day.
• It is getting harder to find the information we are looking for.
Why XML?
• We need search engines to locate the information that we are looking for.
• Most of the WWW documents are in HTML.
• Search engines can bring you tons of pages.• Note that we humans are smart. Most of the times
we can realize the content of a webpage by reading it. But computer programs are not and search engine is a computer program.
XML is the solution.
• HTML describes how to display a page.
• But it does nothing to describe the contents of a page.
• We need a language to convey the content of a web page.
• XML is the solution.
XML
• XML indicates:– What information is contained within a
webpage.– Where that information is on the page.
XML and HTML
• XML is not a replacement for HTML
• XML was designed to describe data in a format that you want and to focus on what data is.
• HTML was designed to display data in a format that you prefer.
• HTML is about displaying information, while XML is about describing information
XML and HTML
• XML and HTML complement each other.
XML describes the data.
HTML displays the data.
• eXtensible• Markup• Language• XML is supported by many platforms and
many tools. • A lot of web applications are using XML
now.
eXtensible Markup Language
XML vs. HTML
<HTML>
<BODY>
<UL>
<LI> 1 kg apple
<LI> 1/2 Sugar
<LI> 1 kg white flour
<LI> 250 g butter
</UL>
<P> Place apples in a bowl.
Toss with flour until covered. then, ...
</BODY>
</HTML>
<RECIPE>
<INGREDIENTS>
<INGREDIENT> 1Kg apple </INGREDIENT>
<INGREDIENT> 1/2Kg Sugar </INGREDIENT>
<INGREDIENT> 1 kg white flour </INGREDIENT>
<INGREDIENT> 250 g butter </INGREDIENT>
</INGREDIENTS>
<INSTRUCTIONS>
<INSTRUCTION> Place apples in a bowl.
</INSTRUCTION>
<INSTRUCTION> Toss with flour until covered.
</INSTRUCTION>
….
</INSTRUCTIONS>
</RECIPE>
XML
• Labels the data
• Structures the data
• Example
Rules for Well-Formatted XML• Every XML document must have a special tag: <?xml
version=“1.0”?> to tell web browser it is an xml file• Every XML document must have a single, all-
enclosing “root tag”• Every XML element must have a corresponding
closing tag• Just as HTML, XML elements must be properly nested• XML tags are case sensitive, <FOOD> and <food> are
different• The value of an attribute must appear in quotation
marks (either double or single quotation marks work)
XML Element Names
• Names can contain letters, numbers and other characters
• Names cannot begin with a number or an underscore
• Names cannot begin with the prefix “XML” or “xml” or “xML” etc.
• Names cannot contain spaces
Good, Bad, and Unparsable• Common errors in XML: misspelling tag names,
have more than one root-level element, forgetting to close an open quote
• If XML file is well-formed, the browser will display the file in a hierarchical fashion, otherwise, cannot load the file
• The XML file could be designed poorly although it is well-formed.
Good, Bad and Unparsable• Bad example:<TVGuide>
<channel>…</channel><time>…</time><title>…</title><description>…</description><channel>…</channel><time>…</time><title>…</title><description>…</description>
</TVGuide>
Good, Bad and Unparsable• Solution:<TVGuide>
<program><channel>…</channel><time>…</time><title>…</title><description>…</description>
</program><program>
<channel>…</channel><time>…</time><title>…</title><description>…</description>
</program></TVGuide>
Design Tips• Think logically and design accordinglyEx. Use <CD>…</CD> for cd collections
• If you want it, tag itEx. Don’t use <Time>10:00pm
<name>..</name> </Time>
Use <Time> <slot>10:00pm</slot> <name>…</name></Time>
• Think genericallyEx. Don’t use <NBC>…</NBC> <ABC>…</ABC> to group different
networks Use <name>NBC</name><name>ABC</name>
• Think hierarchicallyStart with a meaningful root element and work downward to successive
levels of detail
What is XSL?• XSL is a language that allows one to
describe for a browser how to process an XML file.
• XSL can convert an XML file into another format XML file.
• XSL can convert an XML file into a non-XML file.
XSL
• The most common type of XSL processing is to convert XML file into HTML file which can be displayed by browsers. We will focus on this use of XSL.
• XSL is the bridge between XML and HTML.• We can use XSL to have different HTML formats of the
same data represented in XML.• Separating data (contents) from style tags (display
commands).• Example:
