CODEWITHSUNDEEP
xmlxsd
Roman Kos
Roman Kos

Reputation: 285

Understanding xsd:choice with minOccurs attribute

I'm trying to understand how xsd:choice and minOccurs work together. I read this topic, but it just responded to half of my question. For example, I've this type :

<xsd:element name="CAR">
  <xsd:complexType>
    <xsd:sequence>
       <xsd:choice>
        <xsd:element name="A"/>
        <xsd:element name="B"/>
       </xsd:choice>
    </xsd:sequence>
  </xsd:complexType>
</xsd:element>

If I want to make it possible to not specify any of CAR's elements (neither A nor B), I can add minOccurs like this:

<xsd:element name="CAR">
  <xsd:complexType>
    <xsd:sequence>
       <xsd:choice>
        <xsd:element name="A" minOccurs="0"/>
        <xsd:element name="B" minOccurs="0"/>
       </xsd:choice>
    </xsd:sequence>
  </xsd:complexType>
</xsd:element>

But is it true that if I put it on only one element, either A or B, it will result on the same? In other words, is it true that my previous example =

<xsd:element name="CAR">
  <xsd:complexType>
    <xsd:sequence>
       <xsd:choice>
        <xsd:element name="A" minOccurs="0"/>
        <xsd:element name="B"/>
       </xsd:choice>
    </xsd:sequence>
  </xsd:complexType>
</xsd:element>

=

<xsd:element name="CAR">
  <xsd:complexType>
    <xsd:sequence>
       <xsd:choice>
        <xsd:element name="A"/>
        <xsd:element name="B" minOccurs="0"/>
       </xsd:choice>
    </xsd:sequence>
  </xsd:complexType>
</xsd:element>

In these three examples, I'll be able to specify any element (neither A nor B), right?

Upvotes: 4

Views: 3660

Answers (1)

Tomalak
Tomalak

Reputation: 338208

I'd express it a little differently:

<xsd:element name="CAR">
  <xsd:complexType>
    <xsd:choice minOccurs="0">
      <xsd:element name="A" />
      <xsd:element name="B" />
    </xsd:choice>
  </xsd:complexType>
</xsd:element>

But to answer your question, a choice between <A> or <B> where both are optional (minOccurs="0") is logically equivalent to a choice between <A> or <B> where either one is optional.

In other words, one of the conditions of the <xsd:choice> must be fulfilled. By declaring minOccurs="0" on one of the options, you effectively allow that to match when no child is found (i.e. "There is no <B>, so what we have here must be an <A> which is missing, which is OK.")

Upvotes: 5

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