Introduction to XML

Kanda Runapongsa (krunapon@kku.ac.th)

Dept. of Computer EngineeringKhon Kaen University

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Outline What is XML? XML vs. HTML What are in XML Files?

Elements Attributes Entities Comments Processing Instructions

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What is XML? XML stands for eXtensible Markup

Language The standard for data interchange on

the Web XML is a text-based markup language

Identify data using tags which are acted as markup

Tags are surrounded by < and > Example:<To>Students</To>

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HTML vs. XML HTML was designed to display data but

XML was designed to describe (identify) data

Examples: HTML: display the text “Computer

Engineering” in bold<b>Computer Engineering</b>

XML: describe that “Computer Engineering” is a department<dept>Computer Engineering</dept>

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HTML vs. XML (Cont.) HTML tags are predefined but XML

tags are defined by the XML author The XML author uses any XML tags

that make sense for a given application

For applications that use the same XML data, they have to agree on the tag names they intend to use

HTML name tags are case insensitive but XML name tags are case sensitive

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Why XML? Simple and extensible License-free Platform independent International language support Read and edit XML using any

standard text-editing tool

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XML Usage Exchange data XML and B2B (Business to Business)

ebXML: Electronic Business using XML Share data Store data Create new languages

WML: Wireless Markup Language

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Outline What is XML? XML vs. HTML What are in XML Files?

Elements Attributes Entities Comments Processing Instructions

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A Sample XML Document<?xml version=“1.0” encoding=“ISO-8859-1”?

><Note>

<To>Students</To><From>Teacher</From><Course id=“168493”><Name>XML and Web Services</Name><Time>2:00-3:30 PM</Time><Place>Dept. of Computer Engineering</Place>

</Course></Note>

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Elements Represent a logical component of an XML

document Elements can contain

Other elements (sub-elements) Text (character data)

The boundary of each element: marked w/ a tag which Starts with < Ends with >

Example: <To>Students</To>

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Attributes Descriptive information attached to

elements Attributes are set inside the start tag

of an element Example: <Course id=“168493”> What are the difference between

elements and attributes? Containment Number of occurrences

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Entities Some characters are used to

markup text in an XML document <, >

To represent these characters There must be an alternative way

to represent them In XML, entities are used to

these special characters

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Entities for Special CharactersCharacters Entities< &lt;> &gt;& &amp;‘ &apos;“ &quot;

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Comments Comments begin with <!-- and

end with --> Comments can contain any data

except the literal string -- An XML processor is not required

to pass them along to an application

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Processing Instructions Give commands or information to

an application that is processing the XML data

Format:<?target instructions?> target is the name of the application

that is expected to do the processing instructions is a string of characters

that embodies the information or commands for the application to process

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CDATA Sections Instructs the parser to ignore

most markup characters Consider a source code listing in

an XML document. It might contain characters that the XML parser would ordinarily recognize as markup (< and & for example)

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CDATA Sections (Cont.) Example<![CDATA[*p = &q; b = (i <= 3); ]]> Between the start of the section, <!

[CDATA[ and the end of the section, ]]>, all character data is passed directly to the application

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Well-formed XML Documents

A document can only be well-formed if it obeys the syntax of XML

Requirement for well-formed documents Elements must have a closing tag Elements must be properly nested XML documents must have a root element Attribute values must always be quoted

Well-formed XML documents make it easier to process XML data

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Schema of XML Documents

Specify allowed XML elements and the relationships between these elements

Facilitate the validation and processing

Several XML Schema languages have been developed. DTD: Document Type Definition XML Schema