= XML Schema Definition

more expressive than DTDs

same syntax as XML

Referencing the XSD in the XML declaration

• xsi:schemaLocation

  list of pairs: (namespace URI + schema URL)

  schema validates elements and attributes in namespace

  <?xml version="1.0"?>
  <person xmlns="http://www.example.com"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://www.example.com person.xsd"><name> Alice </name>
  </person>

• xsi:noNamespaceSchemaLocation

  schema only validates elements that are not in any namespace

  <?xml version="1.0"?>
  <person
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:noNamespaceSchemaLocation="person.xsd"><name> Alice </name>
  </person>

xsd:schema → only once in root of every XSD-schema document

other elements are in its namespace

usually used with prefixes xsd: or xs:

xsd:element → children of root element

can be the root in an “instance”-XSD-document.

<xsd:elementname="elementName"type="elementType">

possible element types:

<xsd:element ....fixed="value"/>

no other value can be specified

<xsd:element ...default="value"/>

assigned when no other value is specified

<xsd:minExclusive value="..."/>

<xsd:maxExclusive value="..."/>

<xsd:minInclusive value="..."/>

<xsd:maxInclusive value="..."/>

<xsd:enumeration value="..."/>

<xsd:pattern value="..."/>

• use regular expressions as value

  [0-9]

  [a-zA-Z]

  ([a-z])*

  ([a-z])+

  ([a-z]){3}

  day | night

<xsd:whiteSpace value="..."/>

whitespace characters = line feeds, tabs, spaces, carriage returns

possible values:

<xsd:length value="..."/>

<xsd:minLength value="..."/>

<xsd:maxLength value="..."/>

<xsd:element name="age">
<xsd:simpleType> <!-- not named -->
<xsd:restriction base="xsd:integer">
<xsd:minExclusive value="0"/>
<xsd:maxInclusive value="110"/>
</xsd:restriction>
</xsd:simpleType>
</xsd:element><xsd:element name="duration">
<xsd:simpleType> <!-- not named -->
<xsd:restriction base="xsd:integer">
<xsd:minExclusive value="0"/>
<xsd:maxInclusive value="110"/>
</xsd:restriction>
</xsd:simpleType>
</xsd:element>

<xsd:element name="age" type="intervalType"/>
<xsd:element name="duration" type="intervalType"/><xsd:simpleType name="intervalType"> <!-- named -->
<xsd:restriction base="xsd:integer">
<xsd:minExclusive value="0"/>
<xsd:maxInclusive value="110"/>
</xsd:restriction>
</xsd:simpleType>

<person id="E832740"/>

<xsd:element name="person" type="personType"/><xsd:complexType name="personType">
<xsd:attribute name="id" type="xsd:ID"/> <!-- attribute, nothing else -->
</xsd:complexType>

<person id="E832740"> Mantas Šimkus </person>

<xsd:element name="person" type="personType"/><xsd:complexType name="personType">
<xsd:simpleContent>	<!-- wrap to extend string and add an attribute-->
<xsd:extension base="xsd:string">
<xsd:attribute name="id" type="xsd:ID"/>
</xsd:extension>
</xsd:simpleContent>
</xsd:complexType>

<person>
<firstname> Mantas </firstname>
<lastname> Šimkus </lastname>
</person>

<xsd:element name="person" type="personType"/><xsd:complexType name="personType">
<xsd:sequence>
<xsd:element name="firstname" type="xsd:string"/>
<xsd:element name="lastname" type="xsd:string"/>
</xsd:sequence>
</xsd:complexType>

<definition>
Woah I can combine text with <term> elements </term> in here!
</definition>

<xsd:element name="definition" type="definitionType"/><xsd:complexType name="definitionType" mixed="true">
<xsd:sequence>
<xsd:element name="term" type="xsd:string"/>
</xsd:sequence>
</xsd:complexType>

<xsd:attributename="attributeName" type="attributeType"/>

the attribute-type itself is of a simple type

<xsd:attribute ...default="value"/>

<xsd:attribute ...fixed="value"/>

<xsd:attribute ...use="optional"/>

is the default setting

<xsd:attribute ...use="required"/>

Defining the order for children

<xsd:complexType ...>
<xsd:all>
<xsd:element .../>
<xsd:element .../>
</xsd:all>
</xsd:complexType>

all any order, but children must appear exactly once

minOccurs can be set to$\footnotesize \in \{0, 1\}$

choice exactly one child from list allowed to appear

sequence in given order

<xsd:element name="person">
<xsd:complexType name="personType">
<xsd:sequence>
<xsd:element name="firstname" maxOccurs="2" type="xsd:string"/> <!-- child -->
<xsd:element name="lastname" maxOccurs="2" type="xsd:string"/> <!-- child -->
</xsd:sequence>
</xsd:complexType>
</xsd:element>

<xsd:element name="person">
<xsd:complexType name="personType">
<xsd:sequence maxOccurs="2"> <!-- parent -->
<xsd:element name="firstname" type="xsd:string"/>
<xsd:element name="lastname" type="xsd:string"/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>

Warning: the code snippets above have different meaning!

minOccurs min. number of times the element can be a child

maxOccurs max. number of times the element can be a child → can be set to unbounded

of other existing complex types

ie. here any element with the type “personType” can only contain a text:

<xsd:element name="person" type="personType"/><xsd:complexType name="personType">
<xsd:simpleContent>
<xsd:extension base="xsd:string">
<xsd:attribute name="id" type="xsd:ID"/>
</xsd:extension>
</xsd:simpleContent>
</xsd:complexType>

and a student inherits the type from person:

<xsd:element name="student" type="studentType"/><xsd:complexType name="studentType">
<xsd:complexContent>
<xsd:extension base="personType">
<xsd:attribute name="subject" type="xsd:string"/>
</xsd:extension>
</xsd:complexContent>
</xsd:complexType>

<company>
<employees>
<employee emp_id="e1"> <!-- key -->
...
</employee>
...
</employees>
<managers>
<manager mgr_id="e1"> <!-- foreign key -->
...
</manager>
...
</managers>
</company>

<xsd:element name="company" type="companyType">
<xsd:key name="empKey">
<xsd:selector xpath="employees/employee"/>
<xsd:field xpath="@emp_id"/>
</xsd:key>
<xsd:keyref name="empRef" refer="empKey">
<xsd:selector xpath="managers/manager"/>
<xsd:field xpath="@mgr_id"/>
</xsd:keyref>
</xsd:element><xsd:complexType name="companyType">
...
</xsd:complexType>

If not all employees had ids, but all managers did -

• DTD solution

  <employee emp_id="e1"> E </employee>
  <project proj_id="p1"> P </project><manager mgr_id="e1"> M </manager> <!-- manages employee with ID 'e1' -->

  <!ATTLIST employee emp_id ID #REQUIRED>
  <!ATTLIST project proj_id ID #REQUIRED>
  <!ATTLIST manager mgr_id IDREF #REQUIRED><!ELEMENT employee (#PCDATA)>
  <!ELEMENT project (#PCDATA)>
  <!ELEMENT manager (#PCDATA)>

• Only allowes axes child , descendant-or-self at the beginning of a path with special syntax

• Selects Elements (not attributes)