DTD constraints FOR XML

DTD constraints: Declarations and references to DTDs

1. Internal DTD Documentation

<! DOCTYPE root element [definition content]>

2. External DTD documentation

  " DTD file path ">   or "DTD name ""URL for DTD file">

3, thebasic syntax of DTD elements: <! element name category > or <! Element elements name (element content) >

-element is a keyword and cannot be modified

  - element type, must be capitalized! Content is written in three ways:

(1) empty--indicates that the element cannot contain child elements and text, but can have attributes. (2) any--indicates that the element can contain any element content defined in the DTD (3) #PCDATA--can contain any character data, but cannot contain any child elements

combination type, the following modifiers are available:

symbols	Use	Example	Example Description
()	Used to group elements	(Dragon | Jin Yong), (Wang Shuo | yu jie)	Divided into two groups
|	In the list of objects, select a	(Men | women)	means that a man or woman must appear, at least one of them.
+	The object must appear one or more times	(member +)	Indicates that a member must appear, but multiple members can appear
*	This object allows to occur 0 or more times	(Hobby *)	Hobbies can appear two times to many times
?	The object must appear 0 or 1 times	(rookie?)	Rookie can appear, also can not appear, if appear, can appear at most only once
,	Objects must appear in the order specified	(Watermelon, apple, banana)	Watermelon, apples, bananas must appear, and appear in this order

For example:

<! ELEMENT Family (person +, home appliance *) >

<! ELEMENT to  empty>

<! ELEMENT Body (#PCDATA) >

4, the definition of attributes:

Attribute name Type attribute characteristics
... >

Type of property: (1) CDATA (2) ID (3) idref/idrefs (4) enumerated (5) Entity/entities

(1) attribute type-cdata, which indicates that the property value can be any character (including Chinese and numeric)

(2) The attribute type-id, which indicates that the value of the property must be unique, but the value of the property cannot start with a number!

(3) attribute type-idref/idrefs

(4) attribute type-enumerated, define some values beforehand, the value of the property must be within the range of the listed values.

(5) attribute type-entity, entity

Entity definition:
-The entity is used to create an alias for a piece of content that can be referenced in an XML document later in the use of an alias.
-In the DTD definition, one! The entity statement is used to define a body.
-entities can be divided into two types: reference entities and parametric entities. The referencing entity is applied by the XML document, and the parameter entity is applied by the DTD file itself.

① Referencing entities:<! Entity entity name "Solid content" >

" I am a programmer "> .... &copyright;

② parameter entity:<! Entities% entity name "entity Content" >

" name | email| Telephone | address "><! ELEMENT Personal information (%tag_name;| birthday) ><! ELEMENT Customer information (%tag_name;| company name) >

Characteristics of the property:

(1) #REQUIRED, indicating that this attribute must be given, without giving an error
(2) #IMPLIED, indicating that this attribute can be given or not given
(3) #FIXED value, which indicates that the attribute must give a fixed value
(4) Default value, which indicates that if there is no value for this property, a default value value is assigned

DTD actual case:

DTD file:

<! ENTITY AUTHOR"John Doe"><! ENTITY Company"JD Power Tools, Inc."><! ENTITY EMAIL"[email protected]"><! ELEMENT CATALOG (product+) ><!ELEMENT PRODUCT (Specifications+,options?,price+,notes?) ><!attlist PRODUCTNAME CDATA #IMPLIEDCATEGORY (Handtool| table| shop-professional)"Handtool"PARTNUM CDATA #IMPLIEDPLANT (Pittsburgh| milwaukee| Chicago)"Chicago"INVENTORY (Instock| backordered| Discontinued)"Instock"><! ELEMENT Specifications (#PCDATA) ><!attlist specificationsweight CDATA #IMPLIEDPOWER CDATA #IMPLIED><! ELEMENT OPTIONS (#PCDATA) ><!attlist optionsfinish (Metal| polished| Matte)"Matte"ADAPTER (Included| optional| notapplicable)"Included"Case (Hardshell| Soft| notapplicable)"Hardshell"><! ELEMENT Price (#PCDATA) ><!attlist PRICEMSRP CDATA #IMPLIEDWHOLESALE CDATA #IMPLIEDSTREET CDATA #IMPLIEDSHIPPING CDATA #IMPLIED><! ELEMENT NOTES (#PCDATA) >

the corresponding XML:

<?xml version="1.0"encoding="Utf-8"? ><! DOCTYPE CATALOG SYSTEM"PRODUCT.DTD"><CATALOG> <product name="kang Shuai fu mineral water"category="Table"partnum=" A"Plant="Chicago"> <specifications weight=" -"Power=" -"> Here is the details </SPECIFICATIONS> <PRICE> -</PRICE> <PRICE> -</PRICE> </PRODUCT></CATALOG>

DTD constraints FOR XML