Introduction to xml

 eXtensible Markup Language, is a
specification for creating custom
markup languages
 W3C Recommendation
 Primary purpose is to help computers to
share data
 XML is meta-language. This means that
you use it for creating languages.
 XML is an extensive concept.

 Every XML-document is text-based
 => sharing data between different
computers!
 => sharing data in Internet!
 => platform independence!

 Problems with Binary format
› Platform depence
› Firewalls
› Hard to debug
› Inspecting the file can be hard
 Since XML is text-based, it does not have
the problems mentioned above.
 What are the disadvantages in text
format?

 XML is meta language, which you can use
to create your own markup languages.
 There are several XML Markup Languages
made for different purposes
 All the languages have common xml-rules
 Languages: XHTML, OOXML, Open
Document, RSS, SVG, SOAP, SMIL, MathML...
 List:
› http://en.wikipedia.org/wiki/List_of_XML_markup_languag
es

<?xml version="1.0"?>
<!DOCTYPE html
PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<title>Minimal XHTML 1.0 Document</title>
</head>
<body>
<p>This is a minimal <a href="http://www.w3.org/TR/xhtml1/">XHTML 1.0</a>
document.</p>
</body>
</html>

<!DOCTYPE svg
PUBLIC "-//W3C//DTD SVG 1.1//EN"
"http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
<svg width="100%" height="100%" version="1.1"
xmlns="http://www.w3.org/2000/svg">

<circle cx="100" cy="50" r="40" stroke="black"
stroke-width="2" fill="red"/>

</svg>

<!DOCTYPE math:math PUBLIC "-//OpenOffice.org//DTD Modified W3C MathML
1.01//EN" "math.dtd">
<math:math xmlns:math="http://www.w3.org/1998/Math/MathML">
<math:semantics>
<math:mrow>
<math:mi>x</math:mi>
<math:mo math:stretchy="false">=</math:mo>
<math:mfrac>
<math:mrow>
...
</math:mrow>
<math:annotation math:encoding="StarMath 5.0">x = {-b +-sqrt{b^{2}-4{ac}} } over {2
{a}} </math:annotation>
</math:semantics>
</math:math>

<rss version="2.0">
<channel>
<title>W3Schools Home Page</title>
<link>http://www.w3schools.com</link>
<description>Free web building tutorials</description>
<item>
<title>RSS Tutorial</title>
<link>http://www.w3schools.com/rss</link>
<description>New RSS tutorial on W3Schools</description>
</item>
<item>
<title>XML Tutorial</title>
<link>http://www.w3schools.com/xml</link>
<description>New XML tutorial on W3Schools</description>
</item>
</channel>
</rss>

 XML Spy
 EditiX
 Microsoft XML Notepad
 Visual XML
 XML Viewer
 Xeena
 XML Styler, Morphon, XML Writer…

Rules that Apply to Every
XML-Document

 There are two levels of correctness of an
XML document:
1. Well-formed. A well-formed document
conforms to all of XML's syntax rules.
2. Valid. A valid document additionally
conforms to some semantic rules.
 Let's first look at the XML's syntax rules (1).

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<presentation>
<slide number="1">
<name>Introduction to XML</name>
<contents>XML is ...</contents>
</slide>
</presentation>

 XML-declaration is optional in XML 1.0,
mandatory in 1.1.
› Recommendation: use it.
 Version: 1.0 or 1.1
 Encoding: character encoding, default utf-8
 Standalone:
› is the xml-document linked to external markup
declaration
› yes: no external markup declarations
› no: can have external markup declaration (open
issue..)
› default: "no"

<?xml version="1.0" encoding="utf-8" standalone="no"?>
<presentation>
<slide>
</slide>
</presentation>
Same Declaration
<presentation>
<slide>
</slide>
</presentation>

 Element consists of start tag, optional content
and an end tag:
› <name>Introduction to XML</name>
 Start tag
› <name>
 Content
› Introduction to XML
 End tag
› </name>
 Start tag may have attribute
› <slide number="1">

 Only one root - element
 Every element contains starting tag and an ending
tag
 Content is optional: Empty element
› <x></x> 
› <x/>
 Tag – names are case-sensitive:
› <X></x> 
 Elements must be ended with the end tag in
correct order:
› <p><i>problem here</p></i> <!– Error 

 XML elements can have attributes
in the start tag.
 Attributes must be quoted:
› <person sex="female">
› <person sex='female'>
› <gangster name='George "Shotgun" Ziegler'>
› <gangster name="George
"Shotgun" Ziegler">

 Names can contain letters, numbers,
and other characters
 Names must not start with a number or
punctuation character
 Names must not start with the letters xml
(or XML, or Xml, etc)
 Names cannot contain spaces

 XML document is well-formed if it follows
the syntax rules.
 XML document must be well-formed!
› it's not an xml-document, if it does not follow
the rules..

<head>
</head>
<body>
<p>This is a minimal <a href="http://www.w3.org/TR/xhtml1/">XHTML 1.0</a>
document.</p>
</body>
</html>

<head>
</head>
<body>
<jorma>This is a minimal <a href="http://www.w3.org/TR/xhtml1/">XHTML 1.0</a>
document.</jorma>
</body>
</html>

Defining the Structure for XML
documents

 XML document is valid if
› 1) It is well formed AND
› 2) It follows some semantic rules
 XML document is usually linked to an
external file, that has semantic rules for the
document.
› The file can be dtd (.dtd) or schema (.xsd)
 Semantic rules?
› Name of tags, order of elements

 Because of HTML heritage, browsers try
to understand invalid XHTML-pages
 This is not the case in other XML-
languages.
 In general, if XML-document is
invalid, the processing of the document
is cancelled.

 XML has strict rules for WF and Valid
 If application tries to manipulate xml-
document it does not have to try to
understand the possible errors in the
document
 This means that handling xml-files via
programming language is much easier
› If the document is correctly formed,
manipulate it
› If it isn't display error

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