XML Schema Complete Reference, The

24.11. choice Element

The choice element restricts an XML instance to choose one element type from a set of element types. From a database schema perspective, this restricts a set of columns to have one non-null value. This is similar to how unions are implemented in Section 23.5.3.2. Choices, by default, have one element type but can have a minOccurs attribute and a maxOccurs attribute. Listing 24.10 creates a colorSizeChoicesType setting the minOccurs to 0 and maxOccurs to 4. The colorSizeChoicesType allows up to four choices, and they can be of color and/or size.

Listing 24.10. A Complex colorSizeChoicesType XML Document Fragment

<xsd:complexType name="colorSizeChoicesType" block="#all" final="#all" id="colorSizeChoicesType.catalog.cType"> ...