XML and friendsPart 2 - XML Schema

ELAG 2001workshop 8

Jan Erik Kofoed ©BIBSYS Library Automation

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Schema• XML Schema

W3C Recommendation 2 May 2001

• Will replace DTD• Comprehensive system divided into:

– Structures– Data types

• Three parts:– Primer http://www.w3c.org/TR/xmlschema-0/– Structures http://www.w3c.org/TR/xmlschema-1/– Datatypes http://www.w3c.org/TR/xmlschema-2/

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Purchase order example PO (1)<?xml version="1.0"?><purchaseOrder orderDate="1999-10-20" xmlns:xsi="http://www.w3.org/2000/10/XMLSchema-instance"

xsi:noNamespaceSchemaLocation="po.xsd"> <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> <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>

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PO (2) – XML-file, part 1<?xml version="1.0"?>

<purchaseOrder orderDate="1999-10-20" xmlns:xsi="http://www.w3.org/2000/10/XMLSchema-instance" xsi:noNamespaceSchemaLocation="po.xsd">

<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>

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PO (3) XML-file, part 2<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>

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PO (4) DTD<!ELEMENT purchaseOrder (shipTo, billTo, comment, items)>

<!ATTLIST purchaseOrder orderDate CDATA #REQUIRED>

<!ELEMENT shipTo (name, street, city, state, zip)>

<!ATTLIST shipTo country CDATA #REQUIRED>

<!ELEMENT billTo (name, street, city, state, zip)>

<!ATTLIST billTo country CDATA #REQUIRED>

<!ELEMENT comment (#PCDATA)>

<!ELEMENT items (item+)>

<!ELEMENT item (productName, quantity, USPrice, comment?, shipDate?)>

<!ATTLIST item partNum CDATA #REQUIRED>

<!ELEMENT USPrice (#PCDATA)>

<!ELEMENT city (#PCDATA)>

<!ELEMENT name (#PCDATA)>

<!ELEMENT productName (#PCDATA)>

<!ELEMENT quantity (#PCDATA)>

<!ELEMENT shipDate (#PCDATA)>

<!ELEMENT state (#PCDATA)>

<!ELEMENT street (#PCDATA)>

<!ELEMENT zip (#PCDATA)>

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Schema structure

• Schema can be divided into:– Prologue– Element declarations– Type declarations

• Complex Type)

• Simple Type)

• Those may be nested in different manners!

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PO (5) schema, overview<xsd:schema ...><xsd:annotation ...> ... </xsd:annotation><xsd:element name=”purchaseorder” ... /><xsd:element name=”comment” ... /> ...<xsd:complexType name=”PurchaseorderType”> ...</xsd:complexType><xsd:complexType name=”USAddress”> ...</xsd:complexType><xsd:complexType name=”Items”> ...</xsd:complexType><xsd:simpleType name=”SKU”> ... </xsd:simpleType></xsd:schema>

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PO (6) schema, part 1<xsd:schema

xmlns:xsd="http://www.w3.org/2000/10/XMLSchema">

<xsd:annotation> <xsd:documentation> 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"/>

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PO (7) schema, part 2 <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>

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PO (8) schema, part 3 <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" use="fixed" value="US"/>

</xsd:complexType>

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PO (9) schema, part 4 <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"/> </xsd:complexType> </xsd:element> </xsd:sequence> </xsd:complexType>

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PO (10) schema, part 5

<!-- 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>

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Components of a schema

• element – declaration of elements• attribute – declaration of attributes,

must be declared after the elements• complexType – allows a content of elements and

attributes • simpleType – does not allow a content of elements

and attributes• elements may refer to globally declared elements• elements may assign a certain type

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Occurrence of elements and attributes

• Element– minOccurs– maxOccurs– fixed– default

• Attribute– use (optional | prohibited | required | default | fixed) – value

• See, Primer table 1

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Simple Types (1)• 45 predefined types

• New types are made as extensions of those

• Restrictions define the base type

• ”Facet” used to define constraints

– length, minLength, maxLength

– pattern (regular expression)

– enumeration (list of values)

– whiteSpace (preserve | replace | collapse)

– maxInclusive, maxExclusive, minInclusive, minExclusive

– precision, scale

– duration, period

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Simple types (2)• list

– defines a new type as a list of another <xsd:simpleType name=”list_of_numbers”> <xsd:list itemType=”xsd:integer”> </xsd:simpleType>

• union– defines a new type as a union of other types

<xsd:simpleType name=”codes”> <xsd:union memberTypes=”xsd:integer xsd:boolean”> </xsd:simpleType>

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Documentation in schema

• annotation, may include– documentation (free text)– appinfo (information to processes)

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Content models (1)

• Extension of simple types:– <xsd:complexType ...>

<xsd:simpleContent> <xsd:extension base=...>

• Mixed content:– <xsd:complexType mixed=”true”>

• Empty content– Drop declaration of elements in

<xsd:complexType>

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Content models (2)• Sequence

– <xsd:sequence>

• Choice– <xsd:choice>

• All once in arbitrary order– <xsd:all>

• Groups– <xsd:group>– <xsd:attributeGroup>

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Keys

• Unique value– <xsd:unique ...>

<xsd:selector xpath= ...> <xsd:field xpath= ...>

• Keys– <xsd:key ...>

<xsd:selector xpath= ...> <xsd:field xpath= ...>

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Reference to keys

• Declares that one value shall be equal to another declared as key.:– <xsd:keyref refer=... >

<xsd:selector xpath= ...> <xsd:field xpath= ...>

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Include other schemas

• Read another schema:– <xsd:include schemaLocation= ... />

• Read another schema and allow alterations:– <xsd:redefine schemaLocation= ...>

... all corrections must come here ...</xsd:redefine>

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Namespace

• Example:<xsd:schema xmlns:xsd="http://www.w3.org/2000/10/XMLSchema" xmlns="http://example.org/ns/books/" targetNamespace="http://example.org/ns/books/" elementFormDefault="qualified" attributeFormDefault="unqualified”

<xsd:import namespace="http://www.w3.org/XML/1998/namespace" schemaLocation="myxml.xsd"/>

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Unknown content

Unknown content may be declared using any and anyAttribute:

<xsd:complexType name="descType" mixed="true"> <xsd:sequence> <xsd:any namespace=http://www.w3.org/1999/xhtml minOccurs="0" maxOccurs="unbounded” processContents="skip"/> </xsd:sequence> </xsd:complexType>

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Using a Schema in XML

• Use one of two types of XMLSchema-Instance:

<book isbn="0836217462" xmlns:xsi="http://www.w3.org/2000/10/XMLSchema-instance" xsi:noNamespaceSchemaLocation="file:library.xsd">

<book isbn="0836217462" xmlns="http://example.org/ns/books/" xmlns:xsi="http://www.w3.org/2000/10/XMLSchema-instance" xsi:schemaLocation="http://example.org/ns/books/ file:library.xsd">