How to ensure some mandatory and some optional elements under complextype in xml?

Question

I am facing problems in making a complex element, which allows both optional as well as mandatory elements. For the xml below, say h2 is mandatory, while h1 is optional, and the order does not matter.

Case 1:

<root>
<h1/>
<h2/>
</root>

Case 2:

<root>
<h2/>
</root>

Case 3:

<root>
<h2/>
<h1/>
</root>

XSD:

<xs:element name="root">
    <xs:complexType>
           <xs:sequence minOccurs="1" maxOccurs="unbounded">
               <xs:element name="h1" minOccurs="0"></xs:element>
                <xs:element name="h2" minOccurs="1" />
           </xs:sequence>
     </xs:complexType>
</xs:element>

the third case above fails in this xsd, but such case is valid. I need an xsd that is valid for all the above mentioned cases.

Answer 1

Knowing that what you want is:

to make h2 occur atmost 1, while h1 can occur as many times as possible

You could use this XSD in which you are defining that a XML would be valid if its content is something like (RegExpr) <root><h1/>*<h2/><h1/>*</root> .

XSD:

<?xml version="1.0" encoding="iso-8859-1"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <xsd:element name="root">
    <xsd:complexType>
      <xsd:sequence minOccurs="1" maxOccurs="1">
        <xsd:element name="h1" minOccurs="0" maxOccurs="unbounded"/>
        <xsd:element name="h2" minOccurs="1" maxOccurs="1"/>
        <xsd:element name="h1" minOccurs="0" maxOccurs="unbounded"/>        
      </xsd:sequence>
    </xsd:complexType>
  </xsd:element>
</xsd:schema>

---

Valid XML examples:
1)

 <root> <h1/> <h1/> <h2/> <h1/> </root> 

2)

 <root> <h1/> <h2/> </root> 

---

Invalid XML example:
Two <h2/> Elements.

 <root> <h2/> <h1/> <h2/> </root> 

No <h2/> Element.

 <root> <h1/> <h1/> </root>