[Digital Photography] Difference between EXIF and IPTC

As I ponder how to store and catalog my digital photo's, I've wanted to caption my images plus reliabely store date/time. I didn't want to use some application that imports pictures and inevitabely the company would be defunct in 5 years.

In my search, I wandered accross two different meta data types, EXIF and IPTC, that seem to be embedded into the file itself. That is great, I thought. So theoretically, in 10 years from now, I could grab a random image viewer and read my comments.

Questions:
What is the difference between EXIF and IPTC?
Are they competing or complimentary standards?
If competing, is one more dominant than the other (ie will still be used 5,10,20 years from now)?
What have you found to be the easiest way to edit EXIF/IPTC tags?

 

That's perfect. Thx!