XML DTD XSD XSL in 10 minutes

Introduction

XML

XML stands for eXtensible Markup Language
XML is a markup language like HTML
XML is designed to carry data
XML simplifies data sharing
XML tags are not predefined
XML is designed to be self-descriptive
XML is a W3C recommendation
XML is plain text

XML and HTML

XML is not a replacement for HTML
XML and HTML were designed with different goals (XML to transport and store data, HTML to display data)

DTD

Document Type Definition (DTD) are a set of rules which a specific XML document has to conform to.

XSD

XML Schema Definition (XSD) is used to define the elements of an XML document, just like DTD.

Defines the following:

Elements that can appear in a document
Attributes that can appear in a document
Child elements
Order of child elements
Number of child elements
Empty elements or not
Data type for elements and attributes
Default and fixed values for elements

XSD is the successor of DTD:

Extensible future additions
Richer
Written in XML
Support data types
Support namespaces

XSL

EXtensible Stylesheet Language (XSL) is a style sheet language for XML documents.

Describes how to XML document should be displayed.

Consists of:

XSLT (a language that transforms XML documents)
XPath (a language for defining parts of an XML document)
XSL-FO (XSL Formatting Objects)

It can:

Transform XML in XHTML
Filter and sort XML data
Define parts of an XML documents
Format XML data based on its values
Output XML data

XML

Example

Content example:

<message>
    <from>Ben</from>
    <to>Lara</to>
    <subject>Hello</subject>
    <body>Hey there Lara!</body>
</message>

Declaration

<?xml version="1.0" encoding="UTF-16" standalone="yes"?>

or simply

<?xml version="1.0"?>

Encodings: UTF-8, UTF-16, ISO-8859-1, ...

Root element

XML documents always have to start with a root element, that can have as many other elements inside it.

<?xml version="1.0"?>
<journeys>
    <journey>
        ...
    </journey>
    <journey>
        ...
    </journey>
</journeys>

Attributes

XML elements can have attributes which can contain extra data, normally to convey METADATA.

<?xml version="1.0"?>
<books>
  <book id="100">
    <title>Book name</title>
  </book>
</books>

Special characters

Some characters have a special meaning in XML. Thus, if you want them to be displayed as plain text you will need to escape them by using entity references.

< less than
> greater than
& ampersand
' apostrophe
" quotation mark

Comments

Same as HTML.

<!-- This is a comment. -->

Spaces

XML, unlike HTML, preserves multiple spaces.

Other syntax

XML tags are case sensitive
XML elements have to be properly nested (parent always starting before children and ending after children)
Attributes always have to be quoted

DTD

Declaration

DTD in an external file (recommended):

On XML file (books.xml):

<?xml version="1.0"?>
<!DOCTYPE books SYSTEM "books.dtd">

On DTD file (books.dtd):

DTD file has no declaration.

DTD in the same XML file:

<?xml version="1.0"?>
<!DOCTYPE books [
 ... (dtd) ...
]>
... (xml) ...

Example

books.xml

<?xml version="1.0"?>
<books>
  <book id="100">
    <title>Book name</title>
    <publish_date>2015-01-01</publish_date>
    <author>
      <name>Ben</name>
      <age>40</age>
    </author>
  </book>
</books>

books.dtd

<!ELEMENT books (book*)>

<!ELEMENT book (name, publish_date, author)>
  <!ATTLIST book id CDATA #REQUIRED>
  <!ELEMENT title (#PCDATA)>
  <!ELEMENT publish_data (#PCDATA)>
  <!ELEMENT author (name, age)>
    <!ELEMENT name (#PCDATA)>
    <!ELEMENT age (#PCDATA)>

Terminology

!DOCTYPE books defines that the root element is books.

!ELEMENT defines an ELEMENT.
First param: indicates the element name
Second param: what it contains (which can be a value or another element).

(book)* 0 or more books
(book+) 1 or more books
(#PCDATA) text that will be parsed by a parser*
(#CDATA) text that will not be parsed by a parser*

!ATTLIST defines an attribute.
First param: element name
Second param: attribute name
Third param: type of attribute value

CDATA text that will not be parse by a parser*

Fourth param: attribute value

value default value of the attribute
#REQUIRED attribute is required
#IMPLIED attribute is optional
#FIXED value attribute value is fixed

* Difference between PCDATA and CDATA

Validation

XML documents can be validated with xmllint command-line tool.

xmllint --valid books.xml --noout

XSD

Declaration

On XML file (books.xml):

<?xml version="1.0"?>
<books xmlns="http://bookstore.example.com"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://bookstore.example.com books.xsd">

xmlns: namespace
xmlns:xsi: where elements and data type come from
xsi:schemaLocation: schema location. Can also be a relative URL.

On XSD file (books.xsd):

<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
           targetNamespace="http://bookstore.example.com"
           xmlns="http://bookstore.example.com"
           elementFormDefault="qualified">

No namespace is possible as well:

xsi:noNamespaceSchemaLocation="books.xsd"

Example

books.xml

<?xml version="1.0"?>
<books xmlns="http://bookstore.example.com"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://bookstore.example.com books.xsd">
  <book id="100">
    <title>Book name</title>
    <publish_date>2015-01-01</publish_date>
    <author>
      <name>Ben</name>
      <age>40</age>
    </author>
  </book>
</books>

books.xsd

<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
           targetNamespace="http://bookstore.example.com"
           xmlns="http://bookstore.example.com"
           elementFormDefault="qualified">
<xs:element name="books">
  <xs:complexType>
    <xs:sequence>
      <xs:element name="title" type="xs:string" />
      <xs:element name="publish_date" type="xs:date" />
      <xs:element name="author">
        <xs:complexType>
          <xs:sequence>
            <xs:element name="name" type="xs:string" />
            <xs:element name="age" type="xs:integer" />
          </xs:sequence>
        </xs:complexType>
    </xs:sequence>
  </xs:complexType>
</xs:element>

Terminology

xs:element: xml element
xs:complexType: contains other elements
xs:sequence: elements must appear in a sequence

Data types

Most common data types:

string
decimal
integer
boolean
date
time

Validate

XML documents can be validated with xmllint command-line tool.

xmllint --schema books.xsd books.xml --noout

XSL

Declaration

On XML file (books.xml):

<?xml version="1.0" encoding="UTF-8"?>
<?xml-stylesheet type="text/xsl" href="books.xsl"?>

On XSL file (books.xsl):

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

Example

books.xml

<?xml version="1.0"?>
<?xml-stylesheet type="text/xsl" href="books.xsl"?>
<books>
  <book id="100">
    <title>Book name</title>
    <publish_date>2015-01-01</publish_date>
    <author>
      <name>Ben</name>
      <age>40</age>
    </author>
  </book>
</books>

books.xsl

<?xml version="1.0"?>
<xsl:stylesheet version="1.0"
                xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:template match="/">
  <html>
  <body>
    <h1>Books</h1>
    <table>
      <tr>
        <td>Title</td>
        <td>Publish date</td>
        <td>Author</td>
      </tr>
      <xsl:for-each select="books/book">
        <tr>
          <td width="20%"><xsl:value-of select="title"/></td>
          <td width="20%"><xsl:value-of select="publish_date"/></td>
          <td width="20%"><xsl:value-of select="author/name" />
            (age <xsl:value-of select="author/age" />)
          </td>
        </tr>
      </xsl:for-each>
    </table>
  </body>
  </html>
</xsl:template>
</xsl:stylesheet>

Filter

XML output can be filter by adding a select attribute, such as:

<xsl:for-each select="books/book[title='Book title']">

Operators

= (equal)
!= (not equal)
< (less than)
> (greater than)

Sort

<xsl:for-each select="books/book">
<xsl:sort data-type="text" order="descending" select="title"/>

Conditional

<xsl:if test="age &gt; 10 and age &lt; 20">
  Teenager
</xsl:if>

Operators

or
and

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XML DTD XSD XSL in 10 minutes

Table of contents

Introduction

XML

XML and HTML

DTD

XSD

XSL

XML

Example

Declaration

Root element

Attributes

Special characters

Comments

Spaces

Other syntax

DTD

Declaration

DTD in an external file (recommended):

DTD in the same XML file:

Example

Terminology

Validation

XSD

Declaration

Example

Terminology

Data types

Validate

XSL

Declaration

Example

Filter

Operators

Sort

Conditional

Operators

About

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Resources

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