Comment by JKCalhoun

Apple engineers partnered with Sony, Canon, Nokia, Adobe, Microsoft to try and hammer out a specification that addresses when different metadata flavors overlap (EXIF, IPTC, XMP) [1]. It was not comprehensive (to be sure) but covered the most common properties.

As was more or less discussed in the post, EXIF concerns itself more or less with hardware and camera attributes and can be considered authoritative for that domain.

IPTC was added by photojournalism to cover more artistic metadata like a caption, author (photographer), keywords, etc.

Like the one XKCD strip, XMP seems to have come along to try and create a 3rd standard to replace the first two…

[1] https://en.wikipedia.org/wiki/Metadata_Working_Group