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XML Tutorial

XML HOME XML Introduction XML How to use XML Tree XML Syntax XML Elements XML Attributes XML Namespaces XML Display XML HttpRequest XML Parser XML DOM XML XPath XML XSLT XML XQuery XML XLink XML Validator XML DTD XML Schema XML Server XML Examples XML Quiz XML Certificate

XML AJAX

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XML DOM

DOM Introduction DOM Nodes DOM Accessing DOM Node Info DOM Node List DOM Traversing DOM Navigating DOM Get Values DOM Change Nodes DOM Remove Nodes DOM Replace Nodes DOM Create Nodes DOM Add Nodes DOM Clone Nodes DOM Examples

XPath Tutorial

XPath Introduction XPath Nodes XPath Syntax XPath Axes XPath Operators XPath Examples

XSLT Tutorial

XSLT Introduction XSL Languages XSLT Transform XSLT <template> XSLT <value-of> XSLT <for-each> XSLT <sort> XSLT <if> XSLT <choose> XSLT Apply XSLT on the Client XSLT on the Server XSLT Edit XML XSLT Examples

XQuery Tutorial

XQuery Introduction XQuery Example XQuery FLWOR XQuery HTML XQuery Terms XQuery Syntax XQuery Add XQuery Select XQuery Functions

XML DTD

DTD Introduction DTD Building Blocks DTD Elements DTD Attributes DTD Elements vs Attr DTD Entities DTD Examples

XSD Schema

XSD Introduction XSD How To XSD <schema> XSD Elements XSD Attributes XSD Restrictions

XSD Complex

XSD Elements XSD Empty XSD Elements Only XSD Text Only XSD Mixed XSD Indicators XSD <any> XSD <anyAttribute> XSD Substitution XSD Example

XSD Data

XSD String XSD Date XSD Numeric XSD Misc XSD Reference

Web Services

XML Services XML WSDL XML SOAP XML RDF XML RSS

References

DOM Node Types DOM Node DOM NodeList DOM NamedNodeMap DOM Document DOM Element DOM Attribute DOM Text DOM CDATA DOM Comment DOM XMLHttpRequest DOM Parser XSLT Elements XSLT/XPath Functions

XML Schema Tutorial

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What is an XML Schema?

An XML Schema describes the structure of an XML document.

The XML Schema language is also referred to as XML Schema Definition (XSD).

XSD Example

<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">

<xs:element name="note">
  <xs:complexType>
    <xs:sequence>
      <xs:element name="to" type="xs:string"/>
      <xs:element name="from" type="xs:string"/>
      <xs:element name="heading" type="xs:string"/>
      <xs:element name="body" type="xs:string"/>
    </xs:sequence>
  </xs:complexType>
</xs:element>

</xs:schema>

The purpose of an XML Schema is to define the legal building blocks of an XML document:

  • the elements and attributes that can appear in a document
  • the number of (and order of) child elements
  • data types for elements and attributes
  • default and fixed values for elements and attributes

Why Learn XML Schema?

In the XML world, hundreds of standardized XML formats are in daily use.

Many of these XML standards are defined by XML Schemas.

XML Schema is an XML-based (and more powerful) alternative to DTD.

XML Schemas Support Data Types

One of the greatest strength of XML Schemas is the support for data types.

  • It is easier to describe allowable document content
  • It is easier to validate the correctness of data
  • It is easier to define data facets (restrictions on data)
  • It is easier to define data patterns (data formats)
  • It is easier to convert data between different data types

XML Schemas use XML Syntax

Another great strength about XML Schemas is that they are written in XML.

  • You don't have to learn a new language
  • You can use your XML editor to edit your Schema files
  • You can use your XML parser to parse your Schema files
  • You can manipulate your Schema with the XML DOM
  • You can transform your Schema with XSLT

XML Schemas are extensible, because they are written in XML.

With an extensible Schema definition you can:

  • Reuse your Schema in other Schemas
  • Create your own data types derived from the standard types
  • Reference multiple schemas in the same document

XML Schemas Secure Data Communication

When sending data from a sender to a receiver, it is essential that both parts have the same "expectations" about the content.

With XML Schemas, the sender can describe the data in a way that the receiver will understand.

A date like: "03-11-2004" will, in some countries, be interpreted as 3.November and in other countries as 11.March.

However, an XML element with a data type like this:

<date type="date">2004-03-11</date>

ensures a mutual understanding of the content, because the XML data type "date" requires the format "YYYY-MM-DD".

Well-Formed is Not Enough

A well-formed XML document is a document that conforms to the XML syntax rules, like:

  • it must begin with the XML declaration
  • it must have one unique root element
  • start-tags must have matching end-tags
  • elements are case sensitive
  • all elements must be closed
  • all elements must be properly nested
  • all attribute values must be quoted
  • entities must be used for special characters

Even if documents are well-formed they can still contain errors, and those errors can have serious consequences.

Think of the following situation: you order 5 gross of laser printers, instead of 5 laser printers. With XML Schemas, most of these errors can be caught by your validating software.


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