Abstraction in Science, Mathematics, Software, and Markup

Hi Folks,

I am in awe of the power of abstraction.

I wrote a short description of how abstraction is applied in the fields of Science, Mathematics, Software, and Markup:

http://www.xfront.com/Abstraction-in-Science-Mathematics-Software-and-Markup.pdf

I welcome your comments, particularly if you can identify other mechanisms for abstraction in markup.

/Roger