DTD
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 |
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 "[email protected]"
>
<!
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)
>
]>