A notation is a processing instruction that tells the parser what to do with information of a particular format (binary files, image files, sound files, database files and so on) by assigning an external application to process it. The parser tells the application what program is associated with that particular data so that the application knows where to find it should it want to execute it. A notation is referenced by an external entity.
An example of a notation is:
<!NOTATION my_format SYSTEM "http://my_website.com/my_application.exe">
To create, properly associate, and generate a notation
1 Create the notation definition, specifying the XML schema that the notation is contained in, and specifying the external program that the notation uses (see detailed steps below).
2 Specify the External Entity that the notation calls. The External Entity should reference the same XML schema that the notation does.
3 Open the XML diagram that represents the XML Schema that the notation references, and generate the DTD.