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。
The < any > element gives us the ability to expand XML documents through elements that are not specified by schema! The < any > element gives us the ability to expand XML documents through elements that are not specified by schema! The following example is a snippet referenced from a XML schema named “family.xsd”. It shows a declaration for the “person” element. By using the < any > element, we can extend the content of “person” with any element (after < lastname >): Now we want to use the “children” element to extend the “person” element. We can do this in this case, even if the author of the above schema does not declare any “children” elements. Please look at this schema file, named “children.xsd”: The following XML file (named “Myfamily.xml”) uses components from two different schema, “family.xsd” and “children.xsd”: The above XML file is valid because the schema “family.xsd” allows us to extend the “person” element with an optional element after the “lastname” element. Both < any > and < anyAttribute > can be used to make extensible documents! They give the document the ability to contain additional elements that are not declared in the main XML schema. < any > element ¶
<xs:element name="person"> <xs:complexType> <xs:sequence> <xs:element name="firstname" type="xs:string"/> <xs:element name="lastname" type="xs:string"/> <xs:any minOccurs="0"/> xs:sequence> xs:complexType> xs:element>