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xmlxsd
John Livermore
John Livermore

Reputation: 31333

xsd for required and optional elements

What would be the xsd definition to support the following xml?

<xml>
    <RequiredElementA></RequiredElementA>
    <RequiredElementB></RequiredElementB>
    <RequiredElementC></RequiredElementC>
    <OptionalElementD></OptionalElementD>
    <OptionalElementE></OptionalElementE>
</xml>

I want the first 3 to be required, but the last two are optional. Order doesn't matter (but order yes/no not a requirement).

Upvotes: 1

Views: 239

Answers (1)

C. M. Sperberg-McQueen
C. M. Sperberg-McQueen

Reputation: 25054

If the order of children conveys no information, it's usually simplest to fix an order.

<xs:complexType name="fixedOrder">
  <xs:sequence>
    <xs:element ref="RequiredElementA"/>
    <xs:element ref="RequiredElementB"/>
    <xs:element ref="RequiredElementC"/>
    <xs:element ref="RequiredElementD" minOccurs="0"/>
    <xs:element ref="RequiredElementE" minOccurs="0"/>
  </xs:sequence>
</xs:complexType>

If the order carries information (e.g. you are recording the user's rank ordering of A, B, C, with options to include D and E), you can make the order unconstrained. 

<xs:complexType name="variableOrder">
  <xs:all>
    <xs:element ref="RequiredElementA"/>
    <xs:element ref="RequiredElementB"/>
    <xs:element ref="RequiredElementC"/>
    <xs:element ref="RequiredElementD" minOccurs="0"/>
    <xs:element ref="RequiredElementE" minOccurs="0"/>
  </xs:all>
</xs:complexType>

Some people want unconstrained order even when it conveys no information; this makes it possible for data sources not to have to look up the prescribed order, at the cost of making validation somewhat more complex.

Upvotes: 3

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