XML Schema minOccurs / maxOccurs default values

I'm wondering how the XML Schema specification handles these cases:

<xsd:element minOccurs="1" name="asdf"/>

No maxOccurs given -> Is this the cardinality [1..1]?

<xsd:element minOccurs="5" maxOccurs="2" name="asdf"/>

I suppose this is simply invalid?

<xsd:element maxOccurs="2" name="asdf"/>

Is this the cardinality [0..2] or [1..2]?

Is there an "official" definition on how the XML Schema spec handles these cases?

The default values for minOccurs and maxOccurs are 1. Thus:

<xsd:element minOccurs="1" name="asdf"/>

cardinality is [1-1] Note: if you specify only minOccurs attribute, it can't be greater than 1, because the default value for maxOccurs is 1.

<xsd:element minOccurs="5" maxOccurs="2" name="asdf"/>

invalid

<xsd:element maxOccurs="2" name="asdf"/>

cardinality is [1-2] Note: if you specify only maxOccurs attribute, it can't be smaller than 1, because the default value for minOccurs is 1.

<xsd:element minOccurs="0" maxOccurs="0"/>

is a valid combination which makes the element prohibited.

For more info see http://www.w3.org/TR/xmlschema-0/#OccurrenceConstraints

_{New, expanded answer to an old, commonly asked question...}

Default Values

• Occurrence constraints minOccurs and maxOccurs default to 1.

---

Common Cases Explained

<xsd:element name="A"/>

means A is required and must appear exactly once.

---

<xsd:element name="A" minOccurs="0"/>

means A is optional and may appear at most once.

---

 <xsd:element name="A" maxOccurs="unbounded"/>

means A is required and may repeat an unlimited number of times.

---

 <xsd:element name="A" minOccurs="0" maxOccurs="unbounded"/>

means A is optional and may repeat an unlimited number of times.

---

See Also

• W3C XML Schema Part 0: Primer

  > In general, an element is required to appear when the value of > minOccurs is 1 or more. The maximum number of times an element may > appear is determined by the value of a maxOccurs attribute in its > declaration. This value may be a positive integer such as 41, or the > term unbounded to indicate there is no maximum number of occurrences. > The default value for both the minOccurs and the maxOccurs attributes > is 1. Thus, when an element such as comment is declared without a > maxOccurs attribute, the element may not occur more than once. Be sure > that if you specify a value for only the minOccurs attribute, it is > less than or equal to the default value of maxOccurs, i.e. it is 0 or 1. > Similarly, if you specify a value for only the maxOccurs attribute, it must be greater than or equal to the default value of minOccurs, > i.e. 1 or more. If both attributes are omitted, the element must > appear exactly once.

• W3C XML Schema Part 1: Structures Second Edition

   <element
     maxOccurs = (nonNegativeInteger | unbounded)  : 1
     minOccurs = nonNegativeInteger : 1
     >
  
   </element>
  

Short answer:

As written in xsd:

<xs:attribute name="minOccurs" type="xs:nonNegativeInteger" use="optional" default="1"/>
<xs:attribute name="maxOccurs" type="xs:allNNI" use="optional" default="1"/>

If you provide an attribute with number, then the number is boundary. Otherwise attribute should appear exactly once.