minOccurs和maxOccurs的默认值为1。因此:

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

注意:如果只指定minOccurs属性，它不能大于1，因为maxOccurs的默认值是1。

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

无效的

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

注意:如果只指定maxOccurs属性，它不能小于1，因为minOccurs的默认值是1。

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

使元素变为禁止的有效组合。

欲了解更多信息，请参阅http://www.w3.org/TR/xmlschema-0/#OccurrenceConstraints

对一个老问题的新的扩展答案……

默认值

发生约束minOccurs和maxOccurs默认为1。

常见案例说明

<xsd:element name="A"/>

意味着A必须出现一次。

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

意味着A是可选的，最多只能出现一次。

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

意味着A是必需的，可以无限次重复。

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

意味着A是可选的，可以无限次重复。

另请参阅

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>

简短的回答:

用xsd编写:

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

如果您提供一个带有数字的属性，那么这个数字就是边界。否则属性应该只出现一次。