XML documents can reference DTD or XML Schema. Take a look at this XML document called “note.xml”: The following example is an DTD file named “note.dtd” that defines the elements of the above XML document (“note.xml”): Line 1 defines that the note element has four child elements: “to, from, heading, body”. Lines 2-5 define the type of to, from, heading, body element as “# PCDATA”. The following example is an XML Schema file named “note.xsd” that defines the elements of the above XML document (“note.xml”): The note element is a compound type because it contains other child elements. Other elements (to, from, heading, body) are simple types because they do not contain other elements. You will learn more about compound types and simple types in the following sections. This file contains a reference to DTD: This file contains a reference to XML Schema:
In recent years, Geographic Information Systems (GIS) have undergone rapid development in both theoretical and practical dimensions. GIS has been widely applied for modeling and decision-making support across various fields such as urban management, regional planning, and environmental remediation, establishing geographic information as a vital component of the information era. The introduction of the “Digital Earth” concept has further accelerated the advancement of GIS, which serves as its technical foundation. Concurrently, scholars have been dedicated to theoretical research in areas like spatial cognition, spatial data uncertainty, and the formalization of spatial relationships. This reflects the dual nature of GIS as both an applied technology and an academic discipline, with the two aspects forming a mutually reinforcing cycle of progress. A simple XML document: ¶
DTD file ¶
XML Schema ¶
Reference to DTD ¶
Reference to XML Schema ¶
Principles, Technologies, and Methods of Geographic Information Systems
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