An unparsed entity is an external entity whose external reference is not parsed by an XML processor. This means that you can include data in an XML document that is not well-formed XML, such as a graphic file. The UnparsedEntityDecl is named element and a child of type SystemId that identifies the URI for the entity (a URL or a local file location). UnparsedEntityDecl can optionally have a child of type PublicId.
UnparsedEntityDecl can also have a child of type NotationReference, a value element that represents a reference to a notation declaration elsewhere in the XML document. It defines the type of data of the unparsed entity.
An unparsed entity declaration takes the form:
<!ENTITY pic SYSTEM "scheme.gif" NDATA gif>
In this example, the SystemId has a string value of scheme.gif. The value of NotationReference is gif. It refers to a NOTATION defined within the XML document:
<!NOTATION gif SYSTEM "image/gif">
The next entity is included in the DTD example:
<!ENTITY unpsd PUBLIC "//this/is/a/URI/me.gif" "me.gif" NDATA TeX>
This shows the optional PublicId element, which has the string value of //this/is/a/URI/me.gif.