Introduction to XML Schema

Winter 2003

Sources

• XML Schema Part 1: Structures W3C Recommendation 2 May 2001, http://www.w3.org/TR/xmlschema-1/

• XML Schema Part 0 Primer• Definitive XML Schema (Priscilla Walmsley)• Database and Transaction Processing – An

application-oriented Approach (Lewis, Bernstein and Kifer)

XML Schema

• Decouple element types and their names

• Many simple types (xsd:int etc.)• Namespace awareness• Derived types by extension and

restriction• Integrity constraints: key, keyref• “Deterministic”

XML Schema Example File<?xml version="1.0"?><purchaseOrder orderDate="1999-10-20"> <shipTo country="US"> <name>Alice Smith</name> <street>123 Maple Street</street> <city>Mill Valley</city> <state>CA</state> <zip>90952</zip> </shipTo> <billTo country="US"> <name>Robert Smith</name> <street>8 Oak Avenue</street> <city>Old Town</city> <state>PA</state> <zip>95819</zip> </billTo>

XML Schema Example File (Cont.)

<comment>Hurry, my lawn is going wild!</comment> <items> <item partNum="872-AA"> <productName>Lawnmower</productName> <quantity>1</quantity> <USPrice>148.95</USPrice> <comment>Confirm this is

electric</comment> </item> <item partNum="926-AA"> <productName>Baby

Monitor</productName> <quantity>1</quantity> <USPrice>39.98</USPrice> <shipDate>1999-05-21</shipDate> </item> </items></purchaseOrder>

XML Schema for Example File<xsd:schema

xmlns:xsd="http://www.w3.org/2001/XMLSchema">

  <xsd:annotation> <xsd:documentation xml:lang="en"> Purchase order schema for Example.com. Copyright 2000 Example.com. All rights

reserved. </xsd:documentation> </xsd:annotation>  <xsd:element name="purchaseOrder"

type="PurchaseOrderType"/>  <xsd:element name="comment" type="xsd:string"/> 

XML Schema for Example File<xsd:complexType name="PurchaseOrderType"> <xsd:sequence> <xsd:element name="shipTo" type="USAddress"/> <xsd:element name="billTo" type="USAddress"/> <xsd:element ref="comment" minOccurs="0"/> <xsd:element name="items" type="Items"/> </xsd:sequence> <xsd:attribute name="orderDate" type="xsd:date"/> </xsd:complexType>  <xsd:complexType name="USAddress"> <xsd:sequence> <xsd:element name="name" type="xsd:string"/> <xsd:element name="street" type="xsd:string"/> <xsd:element name="city" type="xsd:string"/> <xsd:element name="state" type="xsd:string"/> <xsd:element name="zip" type="xsd:decimal"/> </xsd:sequence> <xsd:attribute name="country" type="xsd:NMTOKEN" fixed="US"/> </xsd:complexType>

XML Schema for Example File <xsd:complexType name="Items"> <xsd:sequence> <xsd:element name="item" minOccurs="0"

maxOccurs="unbounded"> <xsd:complexType> <xsd:sequence> <xsd:element name="productName" type="xsd:string"/> <xsd:element name="quantity"> <xsd:simpleType> <xsd:restriction base="xsd:positiveInteger"> <xsd:maxExclusive value="100"/> </xsd:restriction> </xsd:simpleType> </xsd:element> <xsd:element name="USPrice" type="xsd:decimal"/> <xsd:element ref="comment" minOccurs="0"/> <xsd:element name="shipDate" type="xsd:date"

minOccurs="0"/> </xsd:sequence> <xsd:attribute name="partNum" type="SKU" use="required"/> </xsd:complexType> </xsd:element> </xsd:sequence> </xsd:complexType>

XML Schema for Example File <!-- Stock Keeping Unit, a code for identifying

products --> <xsd:simpleType name="SKU"> <xsd:restriction base="xsd:string"> <xsd:pattern value="\d{3}-[A-Z]{2}"/> </xsd:restriction> </xsd:simpleType> </xsd:schema>

Definitions and Declarations

• Complex types allow elements and attributes.• Simple types cannot have element content and

cannot have attributes. • Definitions create new types (both simple and

complex).• Declarations enable elements and attributes with

specific names and types (both simple and complex) to appear in document instances.

Defining the USAddress Type <xsd:complexType name="USAddress" > <xsd:sequence> <xsd:element name="name" type="xsd:string"/> <xsd:element name="street" type="xsd:string"/> <xsd:element name="city" type="xsd:string"/> <xsd:element name="state" type="xsd:string"/> <xsd:element name="zip" type="xsd:decimal"/> </xsd:sequence> <xsd:attribute name="country" type="xsd:NMTOKEN"

fixed="US"/> </xsd:complexType><billTo country="US"> <name>Robert Smith</name> <street>8 Oak Avenue</street> <city>Old Town</city> <state>PA</state> <zip>95819</zip> </billTo>

Defining PurchaseOrderType<xsd:complexType name="PurchaseOrderType">

<xsd:sequence>

<xsd:element name="shipTo" type="USAddress"/>

<xsd:element name="billTo" type="USAddress"/>

<xsd:element ref="comment" minOccurs="0"/>

<xsd:element name="items" type="Items"/>

</xsd:sequence>

<xsd:attribute name="orderDate" type="xsd:date"/>

</xsd:complexType> 

 

Observe: Attributes can only contain simple types.

Defining PurchaseOrderType

In writing

<xsd:element ref="comment“ minOccurs="0"/>

 

Comment must have been globally defined (not within element or type declaration).

 

 

Restricting Occurrences of Elements and Attributes

 • minOccurs, maxOccurs limit the number of

occurrences• Default is 1.

• Attributes can appear at most once.• use: required (e.g., partNum), optional, or

prohibited. • default attribute: for attributes, supply value if

missing in instance (attribute must be optional)• default element: values supplied only when

instance elements ARE EMPTY (not when MISSING).

Restricting Occurrences of Elements and Attributes: Fixed

 • fixed: ensure that the attributes and elements are

set to particular values (e.g., country is declared with a fixed value US). • Value appears: must be the fixed value.• Value does not appear: the fixed value is

supplied.• default and fixed cannot be concurrently used.

Elements(minOccurs,

maxOccurs) fixed, default 

Attributesuse, fixed, default

Meaning

(1, 1) -, -required, -, - element/attribute must appear once, it may

have any value (1, 1) 37, -required, 37, - element/attribute must appear once, its

value must be 37 (2, unbounded) 37, -N/aelement must appear twice or more, its

value must be 37

(0, 1) -, -optional, -, - element/attribute may appear once, it may

have any value (0, 1) 37, optional, 37, -element/attribute may appear once, if it

does appear its value must be 37, if it

does not appear its value is 37 (0, 1) -, 37optional, -, 37 element/attribute may appear once; if it

does not appear its value is 37, otherwise its value is that given

(0, 0) -, -prohibited, -, - element/attribute must not appear

Restrictions on Global Elements

• Appear at top level of the document

• Cannot use ref• Cannot use minOccurs, maxOccurs

• Cannot mention use

Restricting Simple Types

• Use facets for restricting instances.<xsd:simpleType name="myInteger">

<xsd:restriction base="xsd:integer"> <xsd:minInclusive value="10000"/> <xsd:maxInclusive value="99999"/>

</xsd:restriction>

</xsd:simpleType> • Many facets: length, minLength,

maxLength, pattern, enumeration, whiteSpace …

Restricting Simple Types with a pattern

• "\d{3}-[A-Z]{2}" that is read "three digits followed by a hyphen followed by two upper-case ASCII letters".

<xsd:simpleType name="SKU"> <xsd:restriction base="xsd:string">

<xsd:pattern value="\d{3}-[A-Z]{2}"/>

</xsd:restriction>

</xsd:simpleType>

Restricting Simple Types with an enumeration

• Restrict a simple type by enumerating possibilities.

<xsd:simpleType name="USState"> <xsd:restriction base="xsd:string">

<xsd:enumeration value="AK"/> <xsd:enumeration value="AL"/> < xsd:enumeration value="AR"/> <!-- and so on ... --> </xsd:restriction>

</xsd:simpleType>

Simple Types = Atomic Types, List Types, Union Types

• List types are comprised of sequences of atomic types.

• Three built-in list types: NMTOKENS, IDREFS, and ENTITIES.

• Can create new list types by derivation from existing atomic types.

• Cannot create list types from existing list types, nor from complex types.

List Types

• Type definition::

<xsd:simpleType name="listOfMyIntType"> <xsd:list itemType="myInteger"/>

</xsd:simpleType> • Element with a conforming content:

<listOfMyInt>20003 15037 95977 95945

</listOfMyInt>

List with Facets: List Type for Six US States

• <xsd:simpleType name="USStateList"> <xsd:list itemType="USState"/> </xsd:simpleType> • <xsd:simpleType name="SixUSStates">

<xsd:restriction base="USStateList"> <xsd:length value="6"/>

</xsd:restriction> </xsd:simpleType>

• Conforming element:<sixStates>PA NY CA NY LA AK</sixStates>

Union types: Union Type for Zip codes

<xsd:simpleType name="zipUnion"> <xsd:union memberTypes= "USState listOfMyIntType"/>

</xsd:simpleType>

• Conforming elements of type zipUnion:– <zips>CA</zips– <zips>95630 95977 95945</zips>– <zips>AK</zips>

Anonymous Type Definitions<xsd:complexType name="Items"> <xsd:sequence> <xsd:element name="item" minOccurs="0" maxOccurs="unbounded"> <xsd:complexType> <xsd:sequence> <xsd:element name="productName" type="xsd:string"/> <xsd:element name="quantity"> <xsd:simpleType> <xsd:restriction base="xsd:positiveInteger"> <xsd:maxExclusive value="100"/> </xsd:restriction> </xsd:simpleType> </xsd:element> <xsd:element name="USPrice" type="xsd:decimal"/> <xsd:element ref="comment" minOccurs="0"/> <xsd:element name="shipDate" type="xsd:date"

minOccurs="0"/> </xsd:sequence> <xsd:attribute name="partNum" type="SKU" use="required"/> </xsd:complexType> </xsd:element> </xsd:sequence> </xsd:complexType>

<xsd:element name="internationalPrice"> <xsd:complexType>

<xsd:simpleContent> <xsd:extension base="xsd:decimal"> <xsd:attribute name="currency" type="xsd:string"/> </xsd:extension> </xsd:simpleContent> </xsd:complexType> </xsd:element>

• Conforming element:<internationalPrice currency="EUR"

value="423.46"/>

Elements with a simple content and attributes

No elements

<letterBody> <salutation>Dear Mr.<name>Robert Smith</name>.</salutation> Your order of <quantity>1</quantity> <productName>Baby Monitor</productName> shipped from our warehouse on <shipDate>1999-05-21</shipDate>. .... </letterBody>

Mixed Content Example

<xsd:element name="letterBody"> <xsd:complexType mixed="true"> <xsd:sequence> <xsd:element name="salutation"> <xsd:complexType mixed="true"> <xsd:sequence> <xsd:element name="name" type="xsd:string"/> </xsd:sequence> </xsd:complexType> </xsd:element> <xsd:element name="quantity" type="xsd:positiveInteger"/> <xsd:element name="productName" type="xsd:string"/> <xsd:element name="shipDate" type="xsd:date"

minOccurs="0"/> <!-- etc. --> </xsd:sequence> </xsd:complexType></xsd:element>

Mixed Content Schema

<xsd:element name="internationalPrice"> <xsd:complexType> <xsd:complexContent> <xsd:restriction base="xsd:anyType"> <xsd:attribute name="currency" type="xsd:string"/> <xsd:attribute name="value" type="xsd:decimal"/> </xsd:restriction> </xsd:complexContent> </xsd:complexType></xsd:element>

• Conforming element:<internationalPrice currency="EUR"

value="423.46"/>

Empty Content

<xsd:complexType name="PurchaseOrderType"> <xsd:sequence> <xsd:choice> <xsd:group ref="shipAndBill"/> <xsd:element name="singleUSAddress" type="USAddress"/> </xsd:choice> <xsd:element ref="comment" minOccurs="0"/> <xsd:element name="items" type="Items"/> </xsd:sequence> <xsd:attribute name="orderDate" type="xsd:date"/></xsd:complexType>

<xsd:group name="shipAndBill"> <xsd:sequence> <xsd:element name="shipTo" type="USAddress"/> <xsd:element name="billTo" type="USAddress"/> </xsd:sequence></xsd:group>

Nested Choice and Sequence Groups (single or 2 addresses)

<xsd:complexType name="PurchaseOrderType"> <xsd:all> <xsd:element name="shipTo" type="USAddress"/> <xsd:element name="billTo" type="USAddress"/> <xsd:element ref="comment" minOccurs="0"/> <xsd:element name="items" type="Items"/> </xsd:all> <xsd:attribute name="orderDate" type="xsd:date"/></xsd:complexType>

• Top-level. • Group's children must all be individual elements (no

groups).• Element in the content model may appear more than

once, i.e. the permissible values of minOccurs and maxOccurs are 0 and 1.

ALL GROUPS

<xsd:attributeGroup name="ItemDelivery"> <xsd:attribute name="partNum" type="SKU"

use="required"/> <xsd:attribute name="weightKg"

type="xsd:decimal"/> <xsd:attribute name="shipBy"> <xsd:simpleType> <xsd:restriction base="xsd:string"> <xsd:enumeration value="air"/> <xsd:enumeration value="land"/> <xsd:enumeration value="any"/> </xsd:restriction> </xsd:simpleType> </xsd:attribute></xsd:attributeGroup>

Defining Attribute Groups

<xsd:element name="item" minOccurs="0" maxOccurs="unbounded">

<xsd:complexType> <xsd:sequence> <xsd:element name="productName" type="xsd:string"/> <xsd:element name="quantity"> <xsd:simpleType> <xsd:restriction base="xsd:positiveInteger"> <xsd:maxExclusive value="100"/> </xsd:restriction> </xsd:simpleType> </xsd:element> <xsd:element name="USPrice" type="xsd:decimal"/> <xsd:element ref="comment" minOccurs="0"/> <xsd:element name="shipDate" type="xsd:date" minOccurs="0"/> </xsd:sequence> <!-- attributeGroup replaces individual declarations --> <xsd:attributeGroup ref="ItemDelivery"/> </xsd:complexType></xsd:element>

Using Attribute Groups

• <xsd:element name="shipDate" type="xsd:date" nillable="true"/>

• <shipDate xsi:nil="true"></shipDate>

• An element with xsi:nil="true" may not have any element content but it may still have attributes.

• Useful for representing missing information.

NIL Values

Target Namespaces and Naming

• A target namespace identifies a collection (vocabulary) of type definitions and element declarations. Essentially a logical container.

• The author can decide whether or not the appearance of locally declared elements and attributes in an instance must be qualified by a namespace, using either an explicit prefix or implicitly by default.

Target Namespaces and Naming: The Big Picture

Schema Level:• The XML Schema

namespace (xs, xsd)• Possibly a target

namespace• Possibly a default

xmlns namespace (probably target)

• Possibly other prefixes+namespaces

• Decide on instance qualifications

Instance Level:• Possibly the XSI

namespace• Possibly a default

xmlns namespace (probably a target namespace)

• Probably some other namespace prefixes

• Implement prescribed qualifications.

PO Revisited<?xml version="1.0" encoding="UTF-8"?>

<schema xmlns="http://www.w3.org/2001/XMLSchema" xmlns:po="http://www.example.com/PO1" targetNamespace="http://www.example.com/PO1" elementFormDefault="unqualified" attributeFormDefault="unqualified">

<element name="purchaseOrder" type="po:PurchaseOrderType"/>

<element name="comment" type="string"/> <complexType name="PurchaseOrderType"> <sequence> <element name="shipTo" type="po:USAddress"/> <element name="billTo" type="po:USAddress"/> <element ref="po:comment" minOccurs="0"/> <!-- etc. -->

Refer to local instance elements/attributes

Conforming Instance<apo:purchaseOrder xmlns:apo="http://www.example.com/PO1" orderDate="1999-10-20"> <shipTo country="US"> <name>Alice Smith</name> <street>123 Maple Street</street> <!-- etc. --> </shipTo> <billTo country="US"> <name>Robert Smith</name> <street>8 Oak Avenue</street> <!-- etc. --> </billTo> <apo:comment>Hurry, my lawn is going wild!</apo:comment> <!-- etc. --></apo:purchaseOrder>

• elementFormDefault and attributeFormDefault require that the prefix is not applied to any of the locally declared elements such as shipTo.

Summary

•A sophisticated schema language.

•Namespaces play a major role.

•OO features (abstract classes).

•Deterministic characteristics.

Example Schema<?xml version="1.0" encoding="UTF-8"?>

<xsd:schema targetNamespace="http://www.oded1.com" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns="http://www.oded1.com">

<xsd:element name="salesdata"><xsd:complexType>

<xsd:sequence><xsd:element name="year" type="YearType"

minOccurs="0" maxOccurs="unbounded"/></xsd:sequence>

</xsd:complexType></xsd:element><xsd:complexType name="YearType">

<xsd:sequence><xsd:element name="theyear" type="xsd:string"/><xsd:element name="region" type="RegionType" minOccurs="0"

maxOccurs="unbounded"/></xsd:sequence>

</xsd:complexType>

Example

<xsd:complexType name="RegionType"><xsd:sequence>

<xsd:element name="name" type="xsd:string"/><xsd:element name="sales">

<xsd:complexType><xsd:simpleContent>

<xsd:extension base="xsd:int">

<xsd:attribute name="unit" type="xsd:string"/>

</xsd:extension></xsd:simpleContent>

</xsd:complexType></xsd:element>

</xsd:sequence></xsd:complexType>

</xsd:schema>

Instance<?xml version="1.0" encoding="UTF-8"?>

<s:salesdata xmlns:s="http://www.oded1.com" xmlns:xsi=http://www.w3.org/2001/XMLSchema-instance xsi:schemaLocation="http://www.oded1.com C:\

salesdata.xsd" >

<year><theyear>1996</theyear><region>

<name>central</name><sales unit="millions">34</sales>

</region><region>

<name>east</name><sales unit="millions">34</sales>

</region><region>

<name>west</name><sales unit="millions">12</sales>

</region></year>

</s:salesdata>