what is xml schema ?

DECO 3002 Advanced Technology Integrated Design Computing Studio Tutorial 6 – XML Schema

School of Architecture, Design Science and PlanningFaculty of Architecture

Wei [email protected]

What is XML Schema ?

XML Schema is an XML based description of your data’s business rules – alternative to DTD;

An XML schema expresses the structure of an XML document as DTD does;

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

What XML Schema can while DTD can’t – complex datatype of elements or attributes – think about how to describe an attribute which is an integer ranges from 1 to 100?




Validate your XML documents I:




Validate your XML documents II:

Online Validate (This version is for schema documents with the namespace URI http://www.w3.org/2001/XMLSchema) at http://www.w3.org/2001/03/webdata/xsv

Topologi at http://www.topologi.com/

DTD to Schema Converter at:

LuMriX dtd2xs http://lists.w3.org/Archives/Public/xmlschema-dev/2001Jun/0116.html

Syntext Dtd2Xs http://www.syntext.com/products/index.htm#Dtd2Xs

GUI Oriented:

XML Spy – http://www.xmlspy.com Turbo XML– http://www.extensibility.com




Why DTD is out?

You have to learn different syntax – a syntax different and inconsistent with XML files you are working on;

Limited datatype capability – DTDs support a very limited capability for specifying datatypes. For example, you can not express "I want the <age> element to hold an integer with a range of 1 to 100“;

DTD supports 10 datatypes;

XML Schema supports 44+ datatypes.




Why Schema I?

XML Schema has Support for Data Types – it is easier to describe permissible document content and validate the correctness of data, etc.

XML Schemas use XML Syntax – You don't have to learn another language – you can use your XML editor and parser;

XML Schemas Secure Data Communication – with XML Schemas, the sender can describe the data in a way that the receiver will understand – a “Key”;

XML Schemas are Extensible – just like XML, because they are written in XML –reuse your Schema in other Schemas, create your own data types, etc.




Why Schema II?

Well-Formed is not Enough – a well-formed XML document is a document that conforms to the XML syntax rules;

Even if documents are Well-Formed can have serious consequences because the XML file may violate business rules;

Such as: you order 5 gross of laser printers, and you make a mistake in your XML file – 5 laser printers. With XML Schemas, most of these errors can be caught by your validating software.




Why Schema III – Namespace:

The main reason for using a schema instead of a DTD is the ability to mix namespaces;

An XML namespace is a collection of names, identified by a URI reference [RFC2396], which are used in XML documents as element types and attribute names;

XML document may contain elements and attributes that are defined for and used by multiple software modules – However, such XML files contain multiple markup vocabularies which can pose problems of recognition and collision;

These require components have universal names – XML namespace is the mechanism to solve this problem.




Compare Schema with the Related XML

<?xml version="1.0" encoding="ISO-8859-1"?>

<shiporder orderid="889923"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:noNamespaceSchemaLocation="example.xsd">

<orderperson>John Smith</orderperson>

<shipto>

<name>Ola Nordmann</name>

<address>Langgt 23</address>

<city>4000 Stavanger</city>

<country>Norway</country>

</shipto>

<item>

<title>Empire Burlesque</title>

<note>Special Edition</note>

<quantity>1</quantity>

<price>10.90</price>

</item>

</shiporder>




Compare DTD with the Related Schema

<!ELEMENT BookStore (Book+)>

<!ELEMENT Book (Title, Author, Date, ISBN, Publisher)>

<!ELEMENT Title (#PCDATA)>

<!ELEMENT Author (#PCDATA)>

<!ELEMENT Date (#PCDATA)>

<!ELEMENT ISBN (#PCDATA)>

<!ELEMENT Publisher (#PCDATA)>




DTD:




Schema:




Schema Tips:

For Tag <xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema" targetNamespace="http://www.books.org" xmlns="http://www.books.org" elementFormDefault="qualified">

All Schema has “schema” as root element. And xmlns:xsd =

"http://www.w3.org/2001/XMLSchema" indicates that all XML-Schema elements are to be prefixed with an xsd: tag;

Target nameplace can act as an identification in the data streams when more than one schemas are involved in – it is optional;

The elements and datatypes that are used to construct schemas – schema, element, complexType, sequence, string, etc. are come from the http://www.w3.org/2001/XMLSchema

namespace;

The default namespace is http://www.books.org which is the targetNamespace;

elementFormDefault="qualified“ – This is a directive to any instance documents which conform to this schema: Any elements used by the instance document which were declared in this schema must be namespaced – for example <a:aircraft>Boeing 747</a:aircraft>.




Referencing Schema in XML instance document I:

<?xml version="1.0"?><BookStore xmlns ="http://www.books.org" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.books.org BookStore.xsd"> <Book> <Title>My Life and Times</Title> <Author>Paul McCartney</Author> <Date>July, 1998</Date> <ISBN>94303-12021-43892</ISBN> <Publisher>McMillin Publishing</Publisher> </Book> ...</BookStore>

The line xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance" indicates that we want to use elements defined in the http://www.w3.org/2001/XMLSchema-instance definition;




Referencing Schema in XML instance document II:

First, using a default namespace declaration, tell the schema-validator that all of the elementsused in this instance document come from the http://www.books.org namespace.

Second, with schemaLocation tell the schema-validator that the http://www.books.org namespace is defined by BookStore.xsd,

Note: The xsi:schemaLocation and xsi:noNamespaceSchemaLocation attributes can be used in a document to provide hints as to the physical location of schema documents which may be used forassessment.

Third, tell the schema-validator that the schemaLocation attribute we are using is the one inthe XMLSchema-instance namespace.




No targetNamespace (noNamespaceSchemaLocation

Sometimes you may wish to create a schema but without associating the elements with a namespace;

The targetNamespace attribute is actually an optional attribute of <schema>. Thus, if you don’t want to specify a namespace for your schema then simply don’t use the targetNamespace attribute;

Note that there is no default namespace declaration. So, none of the elements are associated with a namespace;

Note that we do not use xsi:schemaLocation (since it requires a pair of values - a namespace and a URL to the schema for that namespace). Instead, use xsi:noNamespaceSchemaLocation

For Example, in XML instance file: <shiporder orderid="889923" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="example.xsd">




Assembling an Instance Document from More than one schema

An instance document may be composed of elements from multiple schemas.<?xml version="1.0"?><Library xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation= "http://www.book.org Book.xsd http://www.employee.org Employee.xsd"> <Books> <Book xmlns="http://www.book.org"> <Title>My Life and Times</Title> <Author>Paul McCartney</Author> <Date>1998</Date> <ISBN>1-56592-235-2</ISBN> <Publisher>Macmillan Publishing</Publisher> </Book> </Books> <Employees> <Employee xmlns="http://www.employee.org"> <Name>John Doe</Name> <SSN>123-45-6789</SSN> </Employee> </Employees></Library>




Include method:<?xml version="1.0"?><xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema“ targetNamespace="http://www.library.org"xmlns="http://www.library.org“ elementFormDefault="qualified"> <xsd:include schemaLocation="LibraryBook.xsd"/> <xsd:include schemaLocation="LibraryEmployee.xsd"/> <xsd:element name="Library"> <xsd:complexType> <xsd:sequence> <xsd:element name="Books"> <xsd:complexType> <xsd:sequence> <xsd:element ref="Book" maxOccurs="unbounded"/> </xsd:sequence> </xsd:complexType> </xsd:element> <xsd:element name="Employees"> <xsd:complexType> <xsd:sequence> <xsd:element ref="Employee" maxOccurs="unbounded"/> </xsd:sequence> </xsd:complexType> </xsd:element> </xsd:sequence> </xsd:complexType> </xsd:element></xsd:schema>




Building a Schema from Multiple Schema Documents with Different Namespaces – use import method

<?xml version="1.0"?><xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema" targetNamespace="http://www.camera.org" xmlns:nikon="http://www.nikon.com" xmlns:olympus="http://www.olympus.com" xmlns:pentax="http://www.pentax.com" elementFormDefault="qualified"> <xsd:import namespace="http://www.nikon.com" schemaLocation="Nikon.xsd"/> <xsd:import namespace="http://www.olympus.com" schemaLocation="Olympus.xsd"/> <xsd:import namespace="http://www.pentax.com" schemaLocation="Pentax.xsd"/> <xsd:element name="camera"> <xsd:complexType> <xsd:sequence> <xsd:element name="body" type="nikon:body_type"/> <xsd:element name="lens" type="olympus:lens_type"/> <xsd:element name="manual_adapter"

type="pentax:manual_adapter_type"/> </xsd:sequence> </xsd:complexType> </xsd:element><xsd:schema>




References:

http://www.w3schools.com/default.asp http://www.w3.org/XML/Schema http://www.w3.org/TR/xmlschema-0/ http://www.w3.org/TR/xmlschema-1/ http://www.w3.org/TR/xmlschema-2/• Roger L. Costello, XML Technologies Course at http://www.xfront.com/