An Introduction to XML

Based on the W3C XML Recommendations

Agenda• XML Syntax

– XML vs HTML

– Data Types – Elements, Attributes

– White Space – Optional, Mandatory, & Preserved

– Empty Content

– Valid vs Well Formed

• XML Schema– Used to Validate XML data

– Before XML Schema – DTD’s

– Simple Types vs Complex Types

– Restricting data with Regular Expressions

• Namespaces – Avoiding Tag Name Conflicts

• XML Tools– XML Spy and Other Tools

• Corresponding Sample XML, XSD, DTD, XSL, and XHTML files

• XML Resources on the web– http://www.w3schools.com - an excellent site

– http://www.xml.com

– http://www.w3.org

XML vs HTML

As you can see, XML looks similar to HTML.

<?xml version="1.0“?>

<root>

<child>

<subchild attribute=“metadata”>Data</subchild>

</child>

</root>

XML vs HTML

• Unlike HMTL:– XML is Case Sensitive

– Tags must be properly nested

– All start tags must have a corresponding end tag to close the element

– All XML documents must have a root element

– Attrbutes must use quotes (can be single or double)

– White space between tags is preserved

XML vs HTML

• Special Characters– Handled the same way– For Example:

• < > ‘ “ &

• &lt; &gt; &apos; &quot; &amp;

Elements

• XML Elements are extensible and they have parent/child relationships.

• XML elements must follow these naming rules:– Names can contain letters, numbers, underscores, periods, colons,

and hyphens (last three are not normally used in element names)

– Names must not start with a number or punctuation character

– Names must not start with the letters xml (or XML or Xml )

– Names cannot contain spaces

Attributes

• Attributes are normally used to store metadata, data about data, and the real data is stored in elements between the start and end tags.

• Single or Double quotes can be used.

White Space

• White Space Includes:– Carrage returns, Line feeds, Spaces, Horizontal Tabs

• Optional White Space – White space is optional in XML files

• Mandatory White Space – White Space must occur when using attributes

• Preserved White Space – Between start/end tag pairs

Optional White Space

Valid<?xml version="1.0"?>

< root >

< child >

<subchild>Data</subchild>

</child>

</root>

Valid<?xml version="1.0"?><root><child><subchild>Data</subchild></child>

</root>

Mandatory White Space

Valid

<?xml version="1.0"?><root> <child

attribute=“metadata”></root>

Invalid

<?xml version="1.0"?><root>

<childattribute=“metadata”>

</root>

Must have white space here

Preserved White Space

Valid

<?xml version="1.0"?>

<root>

<child>

<subchild>White space between

start/end tag pairs will be preserved</subchild>

</child>

</root>

Empty Content

• IF no data is “held” between a start/ end tag pair, two formats may be used:

<tag></tag>

<tag/>

• The second format is called an Empty Tag (aka Null tag) and commonly used when only an attribute is needed:

<tag attribute=“data”/>

Valid vs Well Formed

• XML data is defined and validated most commonly by:– XML Schemas– DTD’s (Document Type Definition)

• XML data is well formed if it follows the W3C XML Recommendation, Version 1.0– This includes:

• The start/end tags matching up• White space used properly

• NOTE: XML Spy does both checks

XML Schema

• Used to Define and Validate XML

– In order for the XML file to be validated by a schema, the schema’s location is referenced as an attribute of the root element

<FirmOrder … schemaLocation="http://www.telcordia.com/SGG/FO

C:\13.0\Documentation\xsd\firmOrder.xsd"/>

XML Schema• Before XML Schema, most XML

documents were validated against a DTD

<?xml version="1.0"?><xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema" targetNamespace="http://www.sample.org/xml" xmlns="http://www.sample.org/xml" elementFormDefault="qualified"> <xsd:element name=“File"> <xsd:complexType> <xsd:sequence> <xsd:element ref=“Record" minOccurs=“0" maxOccurs=“unbounded"/> </xsd:sequence> </xsd:complexType> </xsd:element> <xsd:element name=“Record"> <xsd:complexType> <xsd:sequence> <xsd:element ref=“Fill minOccurs=“1" maxOccurs=“1”/> </xsd:sequence> </xsd:complexType> </xsd:element> <xsd:element name=“Fill" type="xsd:string"/></xsd:schema>

<!ELEMENT File (Record)*>

<!ELEMENT Record (Fill)>

<!ELEMENT Fill (#PCDATA)>DTD XML

Schema

Mercator Type Tree

XML Schema

• Element Data Types– XML Schema’s Simple Types

• Similar to Items in Mercator• 44 Simple types built-in XML Schema

– XML Schema’s Complex Types• Similar to Groups in Mercator• 36 Complex types built-in XML Schema

– XML Schema’s Attributes• Similar to the Properties of Items and Groups in

Mercator

XML Schema

• Simple Types can be restricted using Regular Expressions:

<xsd:simpleType name="alphaString">

<xsd:restriction base="xsd:string">

<xsd:pattern value="([A-Z]|[a-z]|[ ])*"/>

</xsd:restriction>

</xsd:simpleType>

Namespaces

• XML Namespaces provide a method to avoid element name conflicts.

– Since element names are not predefined as in HTML, often times a name conflict can occur when combining two different documents using the same name for two different elements

Namespaces, cont.

• If the following two XML documents were added together, there would be an element name conflict because both documents contain a <table> element with different content and definition.

<table> <name>Tea Table</name> <width>80</width> <length>120</length></table>

<table> <tr> <td>Apples</td> <td>Bananas</td> </tr></table>

Solving Name Conflicts using a Prefix

<h:table>

<h:tr>

<h:td>Apples</h:td>

<h:td>Bananas</h:td>

</h:tr>

</h:table>

<f:table>

<f:name>African Coffee Table</f:name>

<f:width>80</f:width>

<f:length>120</f:length>

</f:table>

Using Namespaces

<h:table xmlns:h="http://www.w3.org/TR/html4/">

<h:tr>

<h:td>Apples</h:td>

<h:td>Bananas</h:td>

</h:tr>

</h:table>

<f:table xmlns:f="http://www.w3schools.com/furniture">

<f:name>African Coffee Table</f:name>

<f:width>80</f:width>

<f:length>120</f:length>

</f:table>

Namespaces

• URI’s are used as the namespace name– Most commonly used URI is a URL– URL’s by definition are unique to companies– The URL does NOT need to be valid

• They are used for creating uniqueness not validating your tags

• Most companies put “help” documentation about their namespace, tags, and/or XML Schemas

XML Samples

• The next five slides have different types of XML files that correspond to each other:– XML Data Document– XML Schema– DTD (these are not written in XML)– XSL – style sheet

XML Data Sample

<?xml version="1.0"?>

<?xml-stylesheet type="text/xsl" href="xmlxsl.xsl"?>

<root>

<child>

<name>Optional name tag used in this child tag</name>

<description>First description start/end tag pair in child tag</description>

</child>

<child>

<name>Optional name tag used in this child tag</name>

<description>First description start/end tag pair in child tag</description>

<description>Second description start/end tag pair in child tag</description>

</child>

</root>

XML Schema Sample<?xml version="1.0"?><xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema" targetNamespace="http://www.sample.org/xml" xmlns="http://www.sample.org/xml" elementFormDefault="qualified"> <xsd:element name=“root"> <xsd:complexType> <xsd:sequence> <xsd:element ref=“child" minOccurs="0" maxOccurs="unbounded"/> </xsd:sequence> </xsd:complexType> </xsd:element> <xsd:element name="child"> <xsd:complexType> <xsd:sequence> <xsd:element ref="name" minOccurs ="0"/> <xsd:element ref="description" maxOccurs="unbounded"/> </xsd:sequence> </xsd:complexType> </xsd:element> <xsd:element name="name" type="xsd:string"/> <xsd:element name="description" type="xsd:string"/></xsd:schema>

XML DTD Sample

<!ELEMENT root (child)*>

<!ELEMENT child (name?, description+)>

<!ELEMENT name (#PCDATA)>

<!ELEMENT description (#PCDATA)>

Style Sheet (XSL) Sample<?xml version="1.0" encoding="ISO-8859-1"?>

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

<xsl:template match="/">

<html>

<body>

<h2>XHTML Sample</h2>

<table border="1">

<tr bgcolor="gray">

<th>Name</th>

<th>Description</th>

</tr>

<xsl:for-each select="root/child">

<tr>

<td><xsl:value-of select="name" /></td>

<td><xsl:value-of select="description" /></td>

</tr>

</xsl:for-each>

</table>

</body>

</html>

</xsl:template>

</xsl:stylesheet>

XHTML Generated<html>

<body>

<h2>XHTML Sample</h2>

<table border="1">

<tr bgcolor="gray">

<th>Name</th>

<th>Description</th>

</tr>

<tr>

<td>Optional name tag used in this child tag</td>

<td>First description start/end tag pair in child tag</td>

</tr>

<tr>

<td>Optional name tag used in this child tag</td>

<td>First description start/end tag pair in child tag</td>

</tr>

</table>

</body>

</html>

XML Spy

• Accomplishes several XML tasks including:– Editing a variety of XML data graphically– Allowing multiple views including:

• Text, browser, grid, structure (schema design),

– Creates test data from XML Schemas– Generates XML Schemas from XML files– Validates data– Checks data for Well-formedness

Other Tools

• Internet Explorer– Displays XML data using a default style sheet– Checks XML for Well-formedness and displays

error message for troubleshooting

• UltraEdit

XML Resources on the web

• They are hundreds of XML resources on the web.– http://www.w3schools.com (an excellent site)

– http://www.xml.com

– http://www.w3.org

• The easiest was to find data about a specific XML topic or syntax is to type it into google.com

Contact Us

Barry DeBruin

debruinconsulting.com

919-434-5399