• A document is data that you can read.
• Document requirements are a superset of data requirements (e.g., recursion)

The basic problem with documents is that we need to display them in many different forms. This is the problem that SGML was originally designed to solve. XML inherits the solution to that problem.

Example: This presentation.

• Written in XML
• HTML generated using a stylesheet for online publishing
• RTF generated using a different stylesheet