XSD Elements
Defining and working with XML elements in schemas
🧩 XSD Elements
Elements are the building blocks of XML documents. XSD elements define what elements can appear in XML, their data types, and how they relate to each other.
<!-- Simple element definition -->
<xs:element name="title" type="xs:string"/>
Valid XML:
<title>Learning XSD</title>Types of Elements
XSD supports different types of elements for various data structures. Understanding these types helps you model complex XML documents effectively.
Simple Elements
Contain only text, no children
<xs:element name="age" type="xs:integer"/>Complex Elements
Contain child elements or attributes
<xs:element name="person">
<xs:complexType>
<xs:sequence>...</xs:sequence>
</xs:complexType>
</xs:element>Empty Elements
No content, only attributes
<xs:element name="break">
<xs:complexType/>
</xs:element>Mixed Content
Text and child elements combined
<xs:complexType mixed="true">
<xs:sequence>...</xs:sequence>
</xs:complexType>🔹 Simple Elements
Simple elements contain only text data with no child elements or attributes.
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
<!-- String element -->
<xs:element name="name" type="xs:string"/>
<!-- Integer element -->
<xs:element name="age" type="xs:integer"/>
<!-- Decimal element -->
<xs:element name="price" type="xs:decimal"/>
<!-- Boolean element -->
<xs:element name="active" type="xs:boolean"/>
<!-- Date element -->
<xs:element name="birthdate" type="xs:date"/>
</xs:schema>Valid XML:
<name>John Smith</name>
<age>30</age>
<price>19.99</price>
<active>true</active>
<birthdate>1994-05-15</birthdate>🔹 Complex Elements with Sequence
Complex elements contain child elements in a specific order using xs:sequence.
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
<xs:element name="address">
<xs:complexType>
<xs:sequence>
<xs:element name="street" type="xs:string"/>
<xs:element name="city" type="xs:string"/>
<xs:element name="zip" type="xs:string"/>
<xs:element name="country" type="xs:string"/>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:schema>Valid XML:
<address>
<street>123 Main St</street>
<city>New York</city>
<zip>10001</zip>
<country>USA</country>
</address>🔹 Element Occurrence Indicators
Control how many times an element can appear using minOccurs and maxOccurs attributes.
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
<xs:element name="library">
<xs:complexType>
<xs:sequence>
<!-- Required element (default) -->
<xs:element name="name" type="xs:string"/>
<!-- Optional element (0 or 1) -->
<xs:element name="description" type="xs:string" minOccurs="0"/>
<!-- Multiple books (1 or more) -->
<xs:element name="book" type="xs:string" maxOccurs="unbounded"/>
<!-- Optional multiple reviews (0 or more) -->
<xs:element name="review" type="xs:string"
minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:schema>Valid XML:
<library>
<name>City Library</name>
<book>XSD Guide</book>
<book>XML Basics</book>
<book>Web Development</book>
<review>Great collection!</review>
</library>🔹 Default and Fixed Values
Set default values or fixed values for elements.
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
<xs:element name="product">
<xs:complexType>
<xs:sequence>
<xs:element name="name" type="xs:string"/>
<!-- Default value if not provided -->
<xs:element name="quantity" type="xs:integer" default="1"/>
<!-- Fixed value, cannot be changed -->
<xs:element name="currency" type="xs:string" fixed="USD"/>
<!-- Optional with default -->
<xs:element name="inStock" type="xs:boolean"
default="true" minOccurs="0"/>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:schema>Valid XML:
<product>
<name>Laptop</name>
<!-- quantity defaults to 1 -->
<currency>USD</currency>
<!-- inStock defaults to true -->
</product>🔹 Empty Elements
Define elements that have no content but may have attributes.
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
<xs:element name="image">
<xs:complexType>
<xs:attribute name="src" type="xs:string" use="required"/>
<xs:attribute name="alt" type="xs:string"/>
<xs:attribute name="width" type="xs:integer"/>
<xs:attribute name="height" type="xs:integer"/>
</xs:complexType>
</xs:element>
</xs:schema>Valid XML:
<image src="photo.jpg" alt="Photo" width="800" height="600"/>🔹 Mixed Content Elements
Elements that can contain both text and child elements.
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
<xs:element name="paragraph">
<xs:complexType mixed="true">
<xs:sequence>
<xs:element name="bold" type="xs:string"
minOccurs="0" maxOccurs="unbounded"/>
<xs:element name="italic" type="xs:string"
minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:schema>Valid XML:
<paragraph>
This is <bold>important</bold> text with
<italic>emphasis</italic> included.
</paragraph>🔹 Element Reference
Reuse element definitions by referencing them instead of redefining.
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
<!-- Define element once -->
<xs:element name="email" type="xs:string"/>
<!-- Reference it multiple times -->
<xs:element name="contact">
<xs:complexType>
<xs:sequence>
<xs:element ref="email"/>
<xs:element name="phone" type="xs:string"/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name="newsletter">
<xs:complexType>
<xs:sequence>
<xs:element ref="email"/>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:schema>