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DTD
Document Type Definition is declared internally or externally using <!DOCTYPE …>. It is the only schema language that allows entities to be defined.The name of an external DTD file ends with “.dtd”.
This shows an internal DTD.
<?xml version="1.0" ?>
<!DOCTYPE class [
<!ELEMENT class (student*) >
<!ELEMENT student (name,DOB,(top|last)?,description)>
<!ELEMENT name (#PCDATA)>
<!ELEMENT DOB (#PCDATA)>
<!ELEMENT top EMPTY>
<!ELEMENT last EMPTY>
<!ELEMENT description ANY>
<!ATTLIST student
id CDATA #IMPLIED
sex (M|F) #REQUIRED>
<!ENTITY school "Hwa Chung Junior College">
]>
<class>
<student id="H901234" sex="M">
<name>Alex Lee</name>
<DOB>23-03-1990</DOB>
<top/>
<description>studying at &school;.</description>
</student>
<student id="H904321" sex="F">
<name>Mary Chan</name>
<DOB>25-06-1990</DOB>
<description>studying at &school;.</description>
</student>
</class>| A DTD declares all elements, attributes, and entities used. |
| ‘,’ denotes a sequence. When separated by the comma, the child elements must appear in the specified order. ‘|’ denotes a choice. |
| + means one or more. * means zero or more. ? means zero or one. |
The valid attribute types are:
|
The valid attribute defaults are:
|
This demonstrates the use of an external DTD and parameter entities. Parameter entities, to be prefixed by %, are meant to cause substitutions within a DTD and must be declared in an external DTD.
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE p SYSTEM "p.dtd">
<p>
'ANY' allows you to mix <b>tags</b> with <b>parsed character data</b>.
</p><!ENTITY % x.y "p">
<!ENTITY % x.z "ANY">
<!ELEMENT %x.y; %x.z;>
<!ELEMENT b (#PCDATA)>A public DTD is one what is commonly used and widely shared. The XML processor may replace the public ID with a built-in URI. The second string after PUBLIC is a system identifier(URI), and may be used if the public ID is not recognized.
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
</html>(Courtesy of http://en.wikipedia.org/wiki/Document_type_definition#Examples) (modified)
Generally, NMTOKEN, a valid XML name, is one made up of alphanumeric characters, -, _ etc.
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE p [
<!ELEMENT p ANY>
<!ELEMENT b (#PCDATA)>
<!ATTLIST b att NMTOKEN #FIXED "1">
]>
<p>
<b att="1">!1, @1, #1, $1...</b> are valid CDATA but not valid NMTOKEN.
</p>This illustrates how to use attributes declared as ID, IDREF, and IDREFS.
<?xml version="1.0" encoding="UTF-8" ?>
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE p [
<!ELEMENT p ANY>
<!ELEMENT b (#PCDATA)>
<!ATTLIST p ir IDREFS #IMPLIED>
<!ATTLIST b id ID #IMPLIED>
]>
<p ir="b1 b2">
The value of an attribute declared as
<b id="b1">ID</b> must be <b id="b2">unique</b>.
</p>Here are some examples of external entity declarations. The first two are parsed external entities, which means that the parsers retrieve the contents of the files and parse them as if they are internal entities. The third is an unparsed external entity, which means how it is processed is left to the application according to the notation assigned. Here gif is a notation declared elsewhere.
<!ENTITY open-hatch SYSTEM
"http://www.textuality.com/boilerplate/OpenHatch.xml">
<!ENTITY open-hatch PUBLIC
"-//Textuality//TEXT Standard open-hatch boilerplate//EN"
"http://www.textuality.com/boilerplate/OpenHatch.xml">
<!ENTITY hatch-pic SYSTEM
"../grafix/OpenHatch.gif"
NDATA gif >(Courtesy of http://www.w3.org/TR/2008/REC-xml-20081126/#sec-external-ent)
The value of an attribute declared as ENTITY must be an unparsed external entity.
<?xml version="1.0" standalone="no" ?>
<!DOCTYPE img [
<!ELEMENT img EMPTY>
<!ATTLIST img src ENTITY #REQUIRED>
<!ENTITY logo SYSTEM "http://www.xmlwriter.net/logo.gif" NDATA gif>
<!NOTATION gif PUBLIC "gif viewer">
]>
<img src="logo"/>(Courtesy of http://xmlwriter.net/xml_guide/entity_declaration.shtml)