What is exactly the relation between these three?

Ohgma is mentioned as Xarxes's wife, and the Ohgma Infinium supposedly contains information that was granted to Hermaeus Mora by Xarxes. One of MK's forum posts mentions "Ooghama, shield-wife of the Debris". The Debris sounds like a more fitting name for Hermaeus Mora than Xarxes. So is this a polygamous thing? Is Xarxes to Hermaeus Mora what Arden-Sul or Haskill were to Sheogorath? Is Ohgma just an Altmer metaphor or is the Book of Knowledge sapient? Is Xarxes just an aspect of Hermaeus?

It's not even a book, it's weed.

Maybe the book is just named after his wife in honor, I mean Xarxes was pretty much Mora's favorite champion and a lot of Daedras have talked and repect Xarxes, even Mehrunes Dagon gave knowledge and secrets to Xarxes.

I thought Xarxes passed the secret-knowledge given to him by Hermaeus-Mora to Dagon, and MD proceeded to give that knowledge to Mankar? I could just be horribly confused, though.

My theory:

The proto-elves of the Dawn, having been Et'Ada before the division of Aedra and Daedra, gave equal respect to all the great spirits except their king Auriel and their enemy Lorkhan. Xarxes was a champion of Hermaaeus in the dawn times - a collector and maker of secrets. His work was the Oghma Infinium - the book of all knowledge, from which he extracted his "wife" called simply the Oghma (comparatively, the Oghma finitum), the collection of all his favorite moments in history. Eventually, Merish culture started to formalize, and the division between Aedra and Daedra was made, leading to the exile of the Velothi. The Altmer white-washed Xarxes history so that they could keep worshiping their favorite aspect of him - that of lore-keeper of the elven bloodlines.

My theory:

Mora wasn't lying to Septimus: there was a god's heart in that Dwemer lockbox. It just wasn't Lorkhan's. The http://en.wikipedia.org/wiki/Ogmios Infinium is Mora's Heart, cast down to Nirn in mangled echo of a previous kalpa: the kalpa that saw Mora as the Trickster. Xarxes was a Dawn manifestation of the Gardener of Men, ala Shor son of Shor. The wife, Oghma, represents Mora's mangled love for the Mundus, entangled with his divine disillusionment; he marries the history of the World, he names his Heart after bits of the world of mortals, but the very name he chooses hints at his new role in that world. He is the Gardener, the Old Man of the Wood, who tricks men into becoming the elves with whom his sympathies now partially lie.

But yeah, I like MW's too.

My theory is that Hermaeus Mora, being made of discarded ideas of creation, is actually all the remnants of the Kalpas before. Every time a Kalpa ends, the remains and ideas that aren't reused in the next become one with Hermaeus Mora. The Ohgma Infinium's patchwork appearance mimics the patchwork nature of Hermaeus himself. This explains how he is one of the oldest Daedric Princes despite being created from the unused ideas for Mundus: He was actually born at the Second Kalpa. He hungers for knowledge of the future and present because he already knows the past. The Ohgma Infinium is knowledge of the present Kalpa, and that is why it had to be given to Hermaeus.

If anyone can find a way to synthesize those theories into a cohesize whole, I will die a happy (redacted).

Challenge accepted. But it'll have to wait for a bit, 'cause I've got [censored] to do this week.

Oh, and SithisLorkhan: I love your insights. But I believe the line is that Hermaeus did the giving.

Xarxes was married on his work.