Notations

In XML, you may come across data that you would like to include in your documents that is not XML. Notations allow you to include that data in your documents by describing the format it and allowing your application to recognize and handle it.

The format for a notation is:
name system "external_ID">

The name identifies the format used in the document, and the external_id identifies the notation - usually with MIME-types. For example, to include a GIF image in your XML document:

You can also use a "public" identifier, instead of "system". To do this you need to include both a public ID and a URI. Using the GIF example:
  "-//IETF/NOSGML Media Type image/gif//EN"
  "http://www.isi.edu/in-notes/iana/assignments/media-types/image/gif">

On the final page of this article, you will see what a simple DTD would look like within an XML document.