XML introductory notes

XML document structure ( https://www.runoob.com/xml/xml-syntax.html )

1. The first line must be the xml declaration: <?xml version="1.0" encoding="UTF-8"?>  , which defines the version of XML (1.0) and the encoding used (UTF-8: Universal Code, which can display various Language).
2. There is exactly one root node.
3. The writing rules of xml tags are the same as HTML.
4. Use English lowercase for label names, separated by "-" between words: <shop-cart>shopping cart</shop-cart>
5. Put the character "<" in the XML element, an error will occur, such as: message>if salary <1000 then</message>, solution 1, entity reference. 2. CDATA tag: The CDATA part starts with " <![CDATA[ " and ends with " ]]> ".
6. In the sub-elements in the xml multi-level nesting, the order of the tags should be consistent.

example:

hr.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hr SYSTEM "hr.dtd">
<!-- 注释，人力资源管理系统 -->
<hr>
	<employee no="001">
		<name>李白</name>
		<age>21</age>
		<salery>5000</salery>
		<department>
			<dname>开发部</dname>
			<address>北京</address>
		</department>
	</employee>
	
	<employee no="002">
		<name>杜甫</name>
		<age>23</age>
		<salery>7000</salery>
		<department>
			<dname>市场部</dname>
			<address>广州</address>
		</department>
	</employee>
</hr>

 

          

xml semantic constraints: DTD and xml Schema

The purpose of DTD is to define the structure of XML documents: https://www.runoob.com/dtd/dtd-intro.html

1. Bind the .xml and the corresponding .dtd file:

<!DOCTYPE hr SYSTEM "hr.dtd">

     

hr.dtd

<?xml version="1.0" encoding="UTF-8"?>
<!ELEMENT hr (employee+)>
<!ELEMENT employee (name,age,salery,department)>
<!ATTLIST  employee no CDATA "">
<!ELEMENT  name (#PCDATA)>
<!ELEMENT  age (#PCDATA)>
<!ELEMENT  salery (#PCDATA)>
<!ELEMENT  department (dname,address)>
<!ELEMENT  dname (#PCDATA)>
<!ELEMENT  address (#PCDATA)>

xml Schema

Binding:

<hr xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="hr.xsd">

      

Schema file: hr.xsd

<?xml version="1.0" encoding="UTF-8"?>
<schema xmlns="http://www.w3.org/2001/XMLSchema">
	<element name="hr">
		<!--complexType标签的含义是复杂节点，包含子节点是必须使用这个标签 -->
		<complexType>
			<sequence>
				<element name="employee" minOccurs="1" maxOccurs="9999">
					<complexType>
						<sequence>
							<element name="name" type="string"></element>
							<element name="age" >
								<simpleType>
									<restriction base="integer">
										<minInclusive value="18"></minInclusive>
										<maxInclusive value="60"></maxInclusive>
									</restriction>
								</simpleType>
							</element>
							<element name="salery" type="string"></element>
							<element name="department">
								<complexType>
									<sequence>
										<element name="dname" type="string"></element>
										<element name="address" type="string"></element>
									</sequence>
								</complexType>
							</element>
						</sequence>
						<attribute name="no" type="string" use="required"></attribute>
					</complexType>
				</element>
			</sequence>
		</complexType>
	</element>
</schema>