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My understanding is the XTDB is either a fork of Datomic, or was inspired by it? I suppose it's timely, given the top story on HN right now is "Datomic is Free"

• refset 3y ago
  Datomic's "immutable database + Datalog" was definitely the biggest source of inspiration but XTDB has a lot of differences - I wrote this FAQ entry up a few years back: https://docs.xtdb.com/resources/faq/#comparisons https://docs.xtdb.com/resources/faq/#comparisons (note this comparison is for XTDB 1.x and Datomic On-Prem only, so needs revisiting!) Arguably the biggest difference is that XTDB has a schemaless, dynamic core. Having a sane schema is of course important when building complex things, but we believe that the flexibility to experiment with schema (fully) in userspace is essential for moving the state of the art forwards. For instance a lots Clojure users these days prefer relying on https://github.com/metosin/malli https://github.com/metosin/malli for _all_ their schema needs.
• newlisp 3y ago
  They have completely different data models though, XTDB is a schemaless document data store, think mongodb but with SQL/Datalog querying and bi-temporality. Datomic's data model is something they call the 'universal schema' where you just specify the attributes and then create entities however you like from them. Datomic aligns more with how you structure data in Clojure, avoiding the impedance mismatch.