XML Schema: choice and minOccurs

Question

In this example below,

        <xs:complexType>
        <xs:choice minOccurs="3" maxOccurs="unbounded">
            <xs:element ref="Start"/>
            <xs:element ref="Center"/>
            <xs:element ref="End"/>
            <xs:element ref="PI" minOccurs="0"/>
            <xs:element ref="Feature" minOccurs="0" maxOccurs="unbounded"/>
        </xs:choice>
        </xs:complexType>

What happens when choice has minOccurs > 1? Does this mean element "Start" can occur 3 times?

Answer 1

What happens when choice has minOccurs > 1? Does this mean element "Start" can occur 3 times?

Yes <Start> can occur 3 or more times! Having minOccurs of choice as more than 1 allows set of elements to appear more than once or different elements appear multiple times.

Detailed explanation: In the above example you have applied minOccurs as 3 for <Choice> and maxOccurs as unbounded! That means .. Child elements listed under <Choice>, any three of them or any tag repeated three times should appear under their parent! sample XML are listed below:

Let us assume that these set of tags appear under a node called <parent> then:

  <parent>
    <Start>Start1</Start>
    <Center>Center1</Center>
    <End>End1</End>
  </parent>

-------- OR --------

  <parent>
    <Center>Start1</Center>
    <Center>Center1</Center>
    <Feature>End1</Feature>
  </parent>

-------- OR --------

 <parent>
    <Start>Start1</Start>
    <Start>Start1</Start>
    <Start>Start1</Start>
    <Start>Start1</Start>
  </parent>

all the above combinations are valid!

BUT you have also defined minOccurs="0" for 'PI' and 'Feature' ..

This addition causes Validator to pass parent with no child elements as well. ie:

  <parent>
  </parent>

If you remove minOccurs from those two elements then validation forces you to include minimum of 3 tags to be included under parent.

Also having maxOccurs="unbounded" for Feature Element is of no use! The behavior won't change if you add it or take it off..