A Document Type Definition (DTD) defines the legal building blocks of an XML document. It defines the document structure with a list of legal elements and attributes.
<!DOCTYPE root-element [element-declarations]>
Example XML document with an internal DTD:
<?xml version="1.0"?>
<!DOCTYPE note [
<!ELEMENT note (to,from,heading,body)>
<!ELEMENT to (#PCDATA)>
<!ELEMENT from (#PCDATA)>
<!ELEMENT heading (#PCDATA)>
<!ELEMENT body (#PCDATA)>
]>
<note>
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend</body>
</note>
Or with an internal DTD:
<!DOCTYPE note SYSTEM "note.dtd">
The DTD above is interpreted like this:
!DOCTYPE note defines that the root element of this document is note.
!ELEMENT note defines that the note element contains four elements: "to,from,heading,body".
!ELEMENT to defines the to element to be of the type "#PCDATA".
!ELEMENT from defines the from element to be of the type "#PCDATA".
!ELEMENT heading defines the heading element to be of the type "#PCDATA".
!ELEMENT body defines the body element to be of the type "#PCDATA".
PCDATA is text that WILL be parsed by a parser. The text will be examined by the parser for entities and markup.
CDATA is text that will NOT be parsed by a parser
Declaring Elements
<!ELEMENT element-name (element-content)>
Empty Elements
<!ELEMENT element-name EMPTY>
Example:<!ELEMENT br EMPTY>
XML example:<br />
Elements with Parsed Character Data
<!ELEMENT element-name (#PCDATA)>
Example:<!ELEMENT from (#PCDATA)>
Elements with any Contents
<!ELEMENT element-name ANY>
Example:<!ELEMENT note ANY>
Elements with Children (sequences)
<!ELEMENT element-name (child1)> only one
<!ELEMENT element-name (child1+)> minimum one
<!ELEMENT element-name (child1*)> zero or more
<!ELEMENT element-name (child1?)> zero or one
<!ELEMENT element-name (child1,child2,...)>
Example:<!ELEMENT note (to,from,heading,body)>
<!ELEMENT note (to,from,(heading|body))>
Declaring Attributes
<!ATTLIST element-name attribute-name attribute-type default-value>
DTD example:<!ATTLIST payment type CDATA "check">
XML example:<payment type="check" />
| Type | Description |
|---|---|
|
CDATA |
The value is character data |
|
(en1|en2|..) |
The value must be one from an enumerated list |
|
ID |
The value is a unique id |
|
IDREF |
The value is the id of another element |
|
IDREFS |
The value is a list of other ids |
|
NMTOKEN |
The value is a valid XML name |
|
NMTOKENS |
The value is a list of valid XML names |
|
ENTITY |
The value is an entity |
|
ENTITIES |
The value is a list of entities |
|
NOTATION |
The value is a name of a notation |
|
xml: |
The value is a predefined xml value |
| Value | Explanation |
|---|---|
|
value |
The default value of the attribute |
|
#REQUIRED |
The attribute is required |
|
#IMPLIED |
The attribute is not required |
|
#FIXED value |
The attribute value is fixed |
Entities are variables used to define shortcuts to standard text or special characters.
An Internal Entity Declaration
<!ENTITY entity-name "entity-value">
DTD Example:
<!ENTITY writer "Donald Duck.">
<!ENTITY copyright "Copyright W3Schools.">
XML example:<author>&writer;©right;</author>
An External Entity Declaration
<!ENTITY entity-name SYSTEM "URI/URL">
DTD Example:
<!ENTITY writer SYSTEM "http://www.w3schools.com/entities.dtd">
<!ENTITY copyright SYSTEM "http://www.w3schools.com/entities.dtd">
XML example:<author>&writer;©right;</author>
TV Schedule DTD
<!DOCTYPE CATALOG [
<!ENTITY AUTHOR "John Doe">
<!ENTITY COMPANY "JD Power Tools, Inc.">
<!ENTITY EMAIL "jd@jd-tools.com">
<!ELEMENT CATALOG (PRODUCT+)>
<!ELEMENT PRODUCT (SPECIFICATIONS+,OPTIONS?,PRICE+,NOTES?)>
<!ATTLIST PRODUCT
NAME CDATA #IMPLIED
CATEGORY (HandTool|Table|Shop-Professional) "HandTool"
PARTNUM CDATA #IMPLIED
PLANT (Pittsburgh|Milwaukee|Chicago) "Chicago"
INVENTORY (InStock|Backordered|Discontinued) "InStock">
<!ELEMENT SPECIFICATIONS (#PCDATA)>
<!ATTLIST SPECIFICATIONS
WEIGHT CDATA #IMPLIED
POWER CDATA #IMPLIED>
<!ELEMENT OPTIONS (#PCDATA)>
<!ATTLIST OPTIONS
FINISH (Metal|Polished|Matte) "Matte"
ADAPTER (Included|Optional|NotApplicable) "Included"
CASE (HardShell|Soft|NotApplicable) "HardShell">
<!ELEMENT PRICE (#PCDATA)>
<!ATTLIST PRICE
MSRP CDATA #IMPLIED
WHOLESALE CDATA #IMPLIED
STREET CDATA #IMPLIED
SHIPPING CDATA #IMPLIED>
<!ELEMENT NOTES (#PCDATA)>
]>
* Reference to W3C Schools
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