Michael Popescu (myNoSQL) has a couple of posts on resources for Datomic.
Intro Videos to Datomic and Datomic Datalog
and,
I commend the materials you will find there but the white paper in particular, which has the following section:
ATOMIC DATA – THE DATOM
Once you are storing facts, it becomes imperative to choose an appropriate granularity for facts. If you want to record the fact that Sally likes pizza, how best to do so? Most databases require you to update either the Sally record or document, or the set of foods liked by Sally, or the set of likers of pizza. These kind of representational issues complicate and rigidify applications using relational and document models. This can be avoided by recording facts as independent atoms of information. Datomic calls such atomic facts ‘datoms‘. A datom consists of an entity, attribute, value and transaction (time). In this way, any of those sets can be discovered via query, without embedding them into a structural storage model that must be known by applications.
In some views of granularity, the datom “atom” looks like a four-atom molecule to me. 😉 Not to mention that entities/attributes and values can have relationships that don’t involve each other.