This type allows an attribute to have a value specified by a notation declared in the DTD in cases in which you want certain consequences to follow from the attribute. these are usually used as triggers such as when you want to specify a given player for a given file type.

<?xml version = "1.0"
         encoding="UTF-8"
         standalone = "yes"?>
<!DOCTYPE DOCUMENT [
	<!ELEMENT DOCUMENT ANY>
	<!NOTATION mp SYSTEM "movPlayer.exe">
	<!ENTITY BladeRunner SYSTEM "dvds/BR/br.mov" NDATA mp>
	<!ELEMENT MOVIE EMPTY>
	<!ATTLIST MOVIE SOURCE ENTITY #REQUIRED>
	]>

<DOCUMENT>
<MOVIE SOURCE = "BladeRunner"/>
</DOCUMENT>