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The absence of a datum in XML can be expressed either by omitting the element (minOccurs="0" in schema) or by setting it to xsi:nil="true" (nillable=true in schema).

Using minOccurs=0 seem altogether cleaner and more consistent, and it doesn't require the XML to reference the XSD namespace. So what is the benefit of nillable?

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nillable is in the spec because the XML Schema WG had a number of members who saw the world in SQL terms and wanted an explicit equivalent to SQL's null values. It's totally unnecessary in my view: just ignore it and don't use it.

  • When nillable="true" is useful : ibm.com/developerworks/library/ws-tip-null/#N100FA – Laiv May 15 '17 at 10:03
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    @Laiv: You could just as well represent it as <elem><nil /></elem>. But I can see how xsd:nil makes sense in a certain way of thinking, since you can have data types orthogonal to the structure of the XML. – JacquesB May 15 '17 at 13:26
  • If you know that someone has four sons and you don't know the name of the third son, then one way of representing it is <son>Matthew</son><son>Mark</son><son/><son>John</son>. But in general, if you want to model "partial information", then I think you usually want to record something about it, e.g. "unknown" or "not applicable" or "deleted". Invent your own vocabulary to fit the semantics of your particular data. – Michael Kay May 15 '17 at 16:35

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