使用XSD发生指标

Question

XML Schema指定"发生指标"(maxOccurrence,minOccurrence).是否应该使用这些指标的元素(xsd:element,xsd:sequence或xsd:all)的"最佳实践"？

例:

或

<xsd:element name="XList">
    <xsd:complexType>
        <xsd:sequence>
            <xsd:element name="X" type="xsd:token" minOccurs="1" maxOccurs="unbounded" />
        </xsd:sequence>
    </xsd:complexType>
</xsd:element>

要么

<xsd:element name="XList">
    <xsd:complexType>
        <xsd:sequence minOccurs="1" maxOccurs="unbounded">
            <xsd:element name="X" type="xsd:token" />
        </xsd:sequence>
    </xsd:complexType>
</xsd:element>

我想到达:

<XList>
    <X>First</X>
    <X>Second</X>
    <X>Third</X>
    <X>Fourth</X>
    <X>Fifth</X>
...
</XList>

Answer 1

我发现了自己.

我的例子之间的区别乍一看并不是很明显,但如果这个例子稍微复杂一点就有意义了.

以下扩展阐明了差异:

<xsd:element name="XList">
    <xsd:complexType>
        <xsd:sequence>
            <xsd:element name="X" type="xsd:token"
                         minOccurs="1" maxOccurs="1"/>
            <xsd:element name="Y" type="xsd:token"
                         minOccurs="1" maxOccurs="1"/>   
        </xsd:sequence>
    </xsd:complexType>
</xsd:element>

导致

<XList>
    <X>Only X</X>
    <Y>Only Y</Y>
</XList>

而

<xsd:element name="XList">
    <xsd:complexType>
        <xsd:sequence>
            <xsd:element name="X" type="xsd:token"
                         minOccurs="1" maxOccurs="unbounded"/>
            <xsd:element name="Y" type="xsd:token"
                         minOccurs="1" maxOccurs="unbounded"/>   
        </xsd:sequence>
    </xsd:complexType>
</xsd:element>

导致

<XList>
    <X>First X</X>
    <X>Second X</X>
    <X>Third X</X>
    ...
    <Y>First Y</Y>
    <Y>Second Y</Y>
    ...
</XList>

和

<xsd:element name="XList">
    <xsd:complexType>
        <xsd:sequence minOccurs="1" maxOccurs="unbounded" >
            <xsd:element name="X" type="xsd:token"
                         minOccurs="2" maxOccurs="2"/>
            <xsd:element name="Y" type="xsd:token"
                         minOccurs="1" maxOccurs="1"/>   
        </xsd:sequence>
    </xsd:complexType>
</xsd:element>

导致

<XList>
    <X>First X</X>
    <X>Second X</X>
    <Y>First Y</Y>
    <X>Third X</X>
    <X>Fourth X</X>
    <Y>Second Y</Y>
    ...
</XList>

和

<xsd:element name="XList">
    <xsd:complexType>
        <xsd:sequence minOccurs="1" maxOccurs="unbounded" >
            <xsd:element name="X" type="xsd:token"
                         minOccurs="1" maxOccurs="unbounded"/>
            <xsd:element name="Y" type="xsd:token"
                         minOccurs="1" maxOccurs="unbounded"/>   
        </xsd:sequence>
    </xsd:complexType>
</xsd:element>

导致

<XList>
    <X>First X</X>
    <X>Second X</X>
    <X>Third X</X>
    ...
    <Y>First Y</Y>
    <Y>Second Y</Y>
    ...
    <X>Fourth X</X>
    <X>Fifth X</X>
    <X>Sixth X</X>
    ...
    <Y>Third Y</Y>
    <Y>Fourth Y</Y>
    ...
</XList>