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XML basic knowledge concept
2022-07-05 18:45:00 【User 7741497】
XML Basic knowledge concepts
attribute
Name value pairs in the following form :
ID="QD5690"
Attributes are in elements , As shown below , An element can have any number of attributes .
<Patient ID="QD5690">Cromley,Marcia N.</Patient>
CDATA Area
Represents text that should not be validated , As shown below :
<myelementname><![CDATA[
Non-validated data goes here.
You can even have stray "<" or ">" symbols in it.
]]></myelementname>
One CDATA
( Character data ) A section cannot contain a string ]]
>, Because this string marks the end of the section . It also means that CDATA
Sections cannot be nested .
Be careful ,CDATA
The content of part must conform to XML The code specified by the document ,XML The same is true for the rest of the document .
comment
No XML Insert instructions for a part of the document master data . The comment is like this :
<!--Output for the class: GXML.PersonNS7-->
content model
Yes XML An abstract description of the possible contents of an element . Possible content models are as follows :
- Empty content model ( Child elements or text nodes are not allowed )
- Simple content model ( Only text nodes are allowed )
- Complex content model ( Only child elements )
- Mixed content model ( Allow child elements and text nodes )
In all cases , Elements may or may not have attributes ; The phrase content model does not involve the existence or non existence of attributes in elements .
default namespace
The namespace to which any unqualified element in a given context belongs . The added default namespace has no prefix . for example :
<Person xmlns="http://www.person.org">
<Name>Isaacs,Rob G.</Name>
<DOB>1981-01-29</DOB>
</Person>
Because this namespace declaration does not use a prefix , therefore <Person>
、<Name>
and <DOB>
Elements belong to this namespace .
Be careful , Below XML The default namespace is not used , It is actually equivalent to the previous example :
<s01:Person s01:xmlns="http://www.person.org">
<s01:Name>Isaacs,Rob G.</s01:Name>
<s01:DOB>1981-01-29</s01:DOB>
</s01:Person>
DOM
Document object model (DOM) Is said XML And object models in related formats .
DTD( Document type definition )
Included in XML A series of text instructions in a document or external file . It defines all valid elements and attributes that can be used in documents . dtd Don't use XML grammar .
element
An element is usually marked by two ( A start tag and an end tag ) form , May contain text and other elements . The content of the element is everything between these two tags , Include text and any child elements . Here is a complete XML Elements , Include start tag 、 Text content and end tag :
<Patient>Cromley,Marcia N.</Patient>
An element can have any number of attributes and any number of child elements .
An empty element can contain a start tag and an end tag , It can also contain only one tag . The following example is equivalent :
<EndDate></EndDate>
<EndDate/>
In practice , Elements are likely to reference different parts of the data record , for example
<Student level="undergraduate">
<Name>Barnes,Gerry</Name>
<DOB>1981-04-23</DOB>
</Student>
entity
( stay XML In file ) A text unit that represents one or more characters . An entity has the following structure :
&characters;
global element
The concepts of global and local elements apply to documents that use namespaces . The name of the global element and the name of the local element are placed in a separate symbol space . A global element is an element whose type has a global scope , That is, its type is in the corresponding XML Elements defined at the top level of the schema . As <xs:schema>
The element declaration of a child element of an element is considered a global declaration . Any other element declaration is a local element , Unless it passes ref Attribute references the global declaration , This actually makes it a global element .
Attributes can be global , It can also be partial .
local element
It's not the whole thing XML Elements . Local elements do not explicitly belong to any namespace , Unless the element is qualified . See qualifying elements and global elements .
namespace
A namespace is a unique string that defines a domain for an identifier , So as to be based on xml Your application will not confuse one type of document with another . It usually uses URL( Unified resource location ) The form of gives a URI( Unified resource indicator ), It may be related to the actual web The address corresponds to , It may not correspond to . for example ,“http://www.w3.org”
It's a namespace .
Use one of the following syntax to include namespace declarations :
xmlns="your_namespace_here"
pre:xmlns="your_namespace_here"
In both cases , Namespaces are only used in the context of inserting namespace declarations . In the latter case , Namespace and given prefix (pre) Related to . If and only if the element or attribute also has this prefix , The element or attribute belongs to this namespace . for example :
<s01:Person xmlns:s01="http://www.person.com">
<Name>Ravazzolo,Roberta X.</Name>
<DOB>1943-10-24</DOB>
</s01:Person>
Namespace declaration uses s01
Prefix . <Person>
Element also uses this prefix , So this element belongs to this namespace . however ,<Name>
and <DOB>
The element does not explicitly belong to any namespace .
A processing instruction (PI)
An instruction ( In the preface ), Designed to tell applications how to use XML Document or how to deal with it . An example ; This associates style sheets with documents .
<?xml-stylesheet type="text/css" href="mystyles.css"?>
prolog
XML The part before the root element in the document . Preface with XML Statement ( Indicates the use of XML edition ) Start , Then it may include DTD Declarations or schema declarations and processing instructions . ( Technically speaking , Unwanted DTD
Or mode . Besides , Technically speaking , You can put both in the same file .)
root, root element, document element
Every XML Documents require only one element at the outermost layer . This is called the root element 、 Root element or document element . The root element is after the preface .
qualified
If you explicitly assign elements or attributes to namespaces , Then the element or attribute is qualified . Consider the following example , among <Person>
The elements and attributes of are unlimited :
<?xml version="1.0" encoding="UTF-8"?>
<Root>
<s01:Person xmlns:s01="http://www.person.com" GroupID="J1151">
<Name>Frost,Sally O.</Name>
<DOB>1957-03-11</DOB>
</s01:Person>
</Root>
ad locum , Namespace declarations use s01
Prefix . There is no default namespace . <Person>
Element also uses this prefix , So this element belongs to this namespace . <Name>
and <DOB>
Element or <GroupID>
Attribute has no prefix , So they don't explicitly belong to any namespace .
contrary , Consider the following , among <Person>
The elements and attributes of are qualified :
<?xml version="1.0" encoding="UTF-8"?>
<Root>
<Person xmlns="http://www.person.com" GroupID="J1151">
<Name>Frost,Sally O.</Name>
<DOB>1957-03-11</DOB>
</Person>
</Root>
In this case ,<Person>
Element defines a default namespace , This namespace applies to child elements and attributes .
Be careful :XML Mode properties elementFormDefault
Properties and attributeFormDefault
Attributes control whether elements and attributes are qualified in a given schema . stay InterSystems IRIS XML Supporting , Use class parameters to specify whether the element qualifies .
schema
One is a group XML Document specifies the document of meta information , Can be used as DTD An alternative . And DTD equally , You can use patterns to validate specific XML The content of the document . For some applications ,XML The pattern provides a connection with dtd
Several advantages over , Include :
- XML The pattern is effective XML file , Therefore, it is easier to develop tools for operation mode .
- XML Patterns can specify a richer set of features , And contain the type information of the value .
Formally , The schema document is consistent with W3 XML Pattern specification XML file ( stay https://www.w3.org/XML/Schema
). It obeys XML The rules , And use some extra syntax . Usually , The file extension is .xsd
.
style sheet
use XSLT Written documents , Describe how the given XML Convert document to another XML Or others “ Human readable ” Documents .
text node
One or more characters contained between the start element and the corresponding end element . for example :
<SampleElement>
sample text node
</SampleElement>
type
Limitations on data interpretation . stay XML In the pattern , The definition of each element and attribute corresponds to a type .
The type can be simple , It can also be complex .
Each attribute has a simple type . Simple types also mean that there are no attributes and child elements ( Only text nodes ) The elements of . Complex types represent other elements .
The following pattern fragment shows some type definitions :
<s:complexType name="Person">
<s:sequence>
<s:element name="Name" type="s:string" minOccurs="0" />
<s:element name="DOB" type="s:date" minOccurs="0" />
<s:element name="Address" type="s_Address" minOccurs="0" />
</s:sequence>
<s:attribute name="GroupID" type="s:string" />
</s:complexType>
<s:complexType name="s_Address">
<s:sequence>
<s:element name="City" type="s:string" minOccurs="0" />
<s:element name="Zip" type="s:string" minOccurs="0" />
</s:sequence>
</s:complexType>
unqualified
If you don't explicitly assign elements or attributes to namespaces , Then the element or attribute is unqualified .
well-formed XML
follow XML Regular XML Document or fragment , For example, there is an end tag to match a start tag .
XML declaration
Indicates the XML edition ( And optional character sets ) The sentence of . If you include , It must be the first line in the document . An example :
<?xml version="1.0" encoding="UTF-8"?>
XPath
XPath (XML Path to the language ) It's based on XML The expression language of , For from XML Get data in the document . The result can be scalar , It can also be the original document XML subtree .
XSLT
XSLT( Extensible stylesheet language conversion ) It's based on XML Language , Used to describe how a given XML Convert document to another XML Or others “ Human readable ” file .
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