Where to start learning the IDEF1X method of model notation?

Question

I recently started learning about data modeling.

After seeing @MDCCL's diagrams and thoughtful approach here, I'm interested in learning more about IDEF1X. I don't want to pay $200+ for the ISO standard.

So where can I begin to learn this appraoch?

Answer 1

Answer left in comments by bbaird:

IDEF1X is commonly described as a methodology, and perhaps the reason we see it as "another way to represent a model" is that it was among the first and so all other graphical representations that have come since have borrowed from it in one way or another (typically through trying to copy features from ERWin). I've found this to be a good primer on the subject:

IDEF1X Introduction

You can also read the original standard here:

FIPS Standard • IDEF1X