最近几年来，地理信息系统无论是在理论上还是应用上都处在一个飞速发展的阶段。 GIS被应用于多个领域的建模和决策支持，如城市管理、区划、环境整治等等，地理信息成为信息时代重要的组成部分之一； “数字地球”概念的提出，更进一步推动了作为其技术支撑的GIS的发展。 与此同时，一些学者致力于相关的理论研究，如空间感知、空间数据误差、空间关系的形式化等等。 这恰好说明了地理信息系统作为应用技术和学科的两个方面，并且这两个方面构成了相互促进的发展过程。
XML Schema 参考手册 完整 XML Schema 参考手册 The element specifies that child elements can appear in any order, and each child element can appear zero or once. 父元素： Group, complexType, restriction (both simpleContent and complexContent), extension (both simpleContent and complexContent) (? The symbol declares that the element can appear zero or once, while the* symbol declares that the element can appear zero or more times in all elements. ) Attribute Description Id Optional. Unique identifier of the element. MaxOccurs Optional. The maximum number of times an element can appear. The value must be 1. MinOccurs Optional. The minimum number of times an element can appear. The value can be an integer 0 or 1. To specify that the element is optional, set the property to 0. The default value is 1. Any attributes Optional. Specifies any other attributes with the non-schema namespace. The above example indicates that “firstname” and “lastname” elements can appear in any order, and both elements must and can only appear once! The above example indicates that “firstname” and “lastname” elements can appear in any order, and each element can appear zero or once! XML Schema 参考手册 完整 XML Schema 参考手册 Definition and usage ¶
Element information ¶
Grammar ¶
Example 1 ¶
<xs:element name="person"> <xs:complexType> <xs:all> <xs:element name="firstname" type="xs:string"/> <xs:element name="lastname" type="xs:string"/> xs:all> xs:complexType> xs:element>
Example 2 ¶
<xs:element name="person"> <xs:complexType> <xs:all minOccurs="0"> <xs:element name="firstname" type="xs:string"/> <xs:element name="lastname" type="xs:string"/> xs:all> xs:complexType> xs:element>