XML basic knowledge concept

XML Basic knowledge concepts

attribute

Name value pairs in the following form :

ID="QD5690"

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Attributes are in elements , As shown below , An element can have any number of attributes .

<Patient ID="QD5690">Cromley,Marcia N.</Patient>

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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>

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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-->

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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>

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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>

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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>

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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/>

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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>

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entity

( stay XML In file ) A text unit that represents one or more characters . An entity has the following structure :

&characters;

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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"

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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>

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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"?>

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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>

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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>

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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>

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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>

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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"?>

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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 .