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Major components of XML Schema

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== Definition ==

{{quotation | XML Schema: Structures specifies the XML Schema definition language, which offers facilities for describing the structure and constraining the contents of XML 1.0 documents, including those which exploit the [[XML namespace]] facility. The schema language, which is itself represented in XML 1.0 and uses namespaces, substantially reconstructs and considerably extends the capabilities found in XML 1.0 document type definitions (DTDs).}}([http://www.w3.org/TR/xmlschema-1/ XML Schema Part 1: Structures Second Edition])

{{quotation | An XML Schema consists of components such as type definitions and element declarations. These can be used to assess the validity of well-formed element and attribute information items (as defined in [XML-Infoset]), and furthermore may specify augmentations to those items and their descendants.}}([http://www.w3.org/TR/xmlschema-1/ XML Schema Part 1: Structures Second Edition])

XML Schema is considerably more complex, and provide a finer level of control, than the Document Type Definition (DTD) and less elegant than [[Relax NG]]

'''See also''': [[XML Schema tutorial - Basics]]

== Major components of XML Schema ==

The main ingredients of an XML Schema are elements, types and attributes.

'''Elements''' : are declared with the <xsd:element> tag. They can have element-only, mixed, or empty of elements content. Elements can also be restricted to have certain values, i.e. types like:
* xs:string
* xs:decimal
* xs:integer
* xs:boolean
* xs:date
* xs:time
* etc.

Simple types can be combined into more complex types. A complex type can define elements, attributes or data types.

Complex elements are firstly used to define element order, e.g. :
* a sequence (appear in order)
* a choice (any element from a list)
* combined (can occur in any order)

'''Attributes''' are also defined within complex elements: any of the simple types can be used as attribute. The attribute can be optional, required or prohibited.

Read more in [[XML Schema tutorial - Basics]]

== Tools ==

=== Editors ===

* Most modern [[XML editor]]s can handle XML Schemas

=== DTD to XSD Conversion tools ===

; XML editors

* [[Exchanger XML Editor]] (free) can translate from XSD to DTD.
* ... there are other editors who can do conversion

; Online

* [http://www.hitsw.com/xml_utilites/ Online XML Utilities] from HitSoftware let's you convert a DTD (and the other way round) online (free of charge). Currently, registration is required and I didn't test this service anymore - [[User:Daniel K. Schneider|Daniel K. Schneider]] 16:49, 4 December 2010 (CET).

; Free tools that need some installation skills

* [http://www.lumrix.net/dtd2xs.php dtd2x] Free Java class. End users can lauch the class through an HTML page (tested on win XP).

* [http://www.thaiopensource.com/relaxng/trang.html Trang] (written by James Clark). Multi-format schema converter based on RELAX NG. Multiplatform Java-based. (Tested, works).

* [http://www.w3.org/2000/04/schema_hack/ A Conversion Tool from DTD to XML Schema]. Needs Perl installed. A slightly different version is at [http://www.mathling.com/xmlschema/ Mary Holstege]s website. (I tested both and they seem to work).

== In education ==

Certain [[educational modeling language]]s use XML Schema, e.g.
* [[eLML]]
* [[IMS]] and [[SCORM]] Standards, like [[IMS Content Packaging]] or [[IMS Simple Sequencing]]. Note: earlier versions of these standards used broken XSDs in order to be compatible with broken editors like XML Spy.

== Links ==

'''W3C XML Schema 1.0 Specification'''
*[http://www.w3.org/TR/xmlschema-0/ XSD 1.0 Primer]
*[http://www.w3.org/TR/xmlschema-1/ XSD 1.0 Structures]
*[http://www.w3.org/TR/xmlschema-2/ XSD 1.0 Datatypes]
*[http://www.w3.org/XML/Schema#Tools Tools]

'''W3C XML Schema 1.1 Specification'''
*[http://www.w3.org/TR/xmlschema11-1/ XSD 1.1 Structures]
*[http://www.w3.org/TR/xmlschema11-2/ XSD 1.1 Datatypes]

; Various
* [http://www.schemavalid.com/faq/xml-schema.html XML Schema FAQ]
* [http://en.wikipedia.org/wiki/XML_Schema_%28W3C%29 XML Schema (W3C)]

[[Category: XML]]
[[Category: Standards]]
[[Category:web standards]]

XML Schema - Revision history

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