Example
In external DTD elements are declared outside the XML file. They are accessed by specifying the system attributes which may be either the legal .dtd file or a valid URL. To reference it as external DTD, the standalone attribute in the XML declaration must be set as no.
An XML that describes a note that contains property to, from and the message is given below.
<?xml version="1.0" encoding="UTF-8" standalone="no" ?>
<!DOCTYPE note SYSTEM "note.dtd">
<note>
<to>Mr.X</to>
<from>Mr.Y</from>
<message>Stack Overflow is awesome</message>
</note>
External DTD for the above XML, note.dtd is given below
<!DOCTYPE note [
<!ELEMENT note (to,from,message>
<!ELEMENT to (#PCDATA)>
<!ELEMENT from (#PCDATA)>
<!ELEMENT message (#PCDATA)>
]>
