这段Schema是什么意思?(摘自java.sun.com的j2ee命名空间)
- <xsd:element name="web-app" type="j2ee:web-appType">
- <xsd:unique name="web-app-servlet-name-uniqueness">
<xsd:selector xpath="j2ee:servlet" />
<xsd:field xpath="j2ee:servlet-name" />
</xsd:unique>
+ <xsd:unique name="web-app-filter-name-uniqueness">
<xsd:selector xpath="j2ee:filter" />
<xsd:field xpath="j2ee:filter-name" />
</xsd:unique>
+ <xsd:unique name="web-app-ejb-local-ref-name-uniqueness">
<xsd:selector xpath="j2ee:ejb-local-ref" />
<xsd:field xpath="j2ee:ejb-ref-name" />
</xsd:unique>
+ <xsd:unique name="web-app-ejb-ref-name-uniqueness">
<xsd:selector xpath="j2ee:ejb-ref" />
<xsd:field xpath="j2ee:ejb-ref-name" />
</xsd:unique>
+ <xsd:unique name="web-app-resource-env-ref-uniqueness">
<xsd:selector xpath="j2ee:resource-env-ref" />
<xsd:field xpath="j2ee:resource-env-ref-name" />
</xsd:unique>
+ <xsd:unique name="web-app-message-destination-ref-uniqueness">
<xsd:selector xpath="j2ee:message-destination-ref" />
<xsd:field xpath="j2ee:message-destination-ref-name" />
</xsd:unique>
+ <xsd:unique name="web-app-res-ref-name-uniqueness">
<xsd:selector xpath="j2ee:resource-ref" />
<xsd:field xpath="j2ee:res-ref-name" />
</xsd:unique>
+ <xsd:unique name="web-app-env-entry-name-uniqueness">
<xsd:selector xpath="j2ee:env-entry" />
<xsd:field xpath="j2ee:env-entry-name" />
</xsd:unique>
+ <xsd:key name="web-app-role-name-key">
<xsd:selector xpath="j2ee:security-role" />
<xsd:field xpath="j2ee:role-name" />
</xsd:key>
+ <xsd:keyref name="web-app-role-name-references" refer="j2ee:web-app-role-name-key">
<xsd:selector xpath="j2ee:servlet/j2ee:security-role-ref" />
<xsd:field xpath="j2ee:role-link" />
</xsd:keyref>
</xsd:element>
这是看不懂的部分,全文见http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd
请教各位大侠,这个unique是什么意思,在这里起什么作用,同样不懂的还有key、keyref、selector和field标签。