<minzero xsi:nil="true"><minzero>
而不能直接將minzero這個元素去掉
（注意：xsi:nil="true"或者xsi:nil="1"應(yīng)該就是表示這個元素為空）
minOccurs="0"：該元素可以直接被省略掉，但是不能讓該元素的值為空，也就是說，不能：
<minzero xsi:nil="true"><minzero>
In a WSDL, XML Schema is the section where it define the message format for each operations, which eventually become the real API that users are interested. And it is the most tricky part of the WSDL. Nowadays there are many tools that you can design and use WSDLs without any needs in knowing the meaning of a single line of the WSDL. But there are situations that you may find it is better you have some knowledge in XML Schema section and in WSDL overall.
For this post I m taking a simple example of use of nillable=”true” and minOccurs=”0″. Take the following example.
<xs:element name="myelements">
<xs:complexType>
<xs:sequence>
<xs:element name="nonboth" type="xs:string"/>
<xs:element minOccurs="0" name="minzero" type="xs:int"/>
<xs:element name="nilint" nillable="true" type="xs:int"/>
<xs:element name="nilstring" nillable="true" type="xs:string"/>
<xs:element minOccurs="0" name="minzeronil" nillable="true" type="xs:string"/>
</xs:sequence>
</xs:complexType>
</xs:element>Just ignore the meaning of what nillable and minOccurs attributes for now. You can safely say the following XML is valid for the above Schema.
<myelements>
<nonboth>i can't be either nil nor skipped<nonboth>
<minzero>3<minzero>
<nilint><nilint>
<nilstring>i can have null, but i cant skipeed</nilstring>
<minzeronil>i can be skipped and have the nil value<minzeronil>
</myelements>Take the first element ‘nonboth’ in the schema, It has not any minOccurs or nillable attribute. By default minOccurs equal to 1 and nillable equal to false. That mean it can’t have nil value nor it can not be removed from the xml.
Is that making an element nil and removing the element from the XML is same? No. Take the second element in the schema ‘minzerostring’. There you have minOccurs =”0″ but there are no nillable=”true”, mean it is non-nillable. The idea is whenever you don’t want that element in your xml, you can’t have the element keeping empty like
<minzero xsi:nil="true"><minzero>But you can remove the whole element from the XML (since it is minOccurs=0).The opposite of the above scenario is nillable=”true” but minOccurrs != 0. Check the ‘nilint’ element in the schema. There you can’t skip the element ‘nilint’, you have to have the element <nilint/> but it can hold a nil value.
<nilint xsi:nil="true"></nilint>
or simply
<minzero/>Since you don’t have that xsi:nil=”1″ this is not a nil value, so the condition nillable=”false” condition is preserved. But unlike for string when you set an empty element for an integer, it doesn’t sound correct. So in practice whenever some schema says non-nillable you should set some valid value.The last one is ‘minzeronil’ element which is both nillable=”true” and minOccurs=”0″. Whenever you don’t need to set a value for this element, you have the choice of either skipping the element or setting the value of the element to nil. It is obvious rather than setting a nil value it is better you just skip the element to make the XML shorter. This is really needed specially in web services where you need the payload to be minimum as much as possible.
Say you have to prepare the XML and you don’t have valid values for any of the element. So this can be the optimum XML you can create.
