Datomish is a persistent, embedded knowledge base. It's written in ClojureScript, and draws heavily on [DataScript](https://github.com/tonsky/datascript) and [Datomic](http://datomic.com).
Datomish compiles into a single JavaScript file, and is usable both in Node (on top of `promise_sqlite`) and in Firefox (on top of `Sqlite.jsm`). It also works in pure Clojure on the JVM on top of `jdbc-sqlite`.
There's an example Firefox restartless add-on in the [`addon`](https://github.com/mozilla/datomish/tree/master/addon) directory; build instructions are below.
Datomish is intended to be a flexible relational (not key-value, not document-oriented) store that doesn't leak its storage schema to users, and doesn't make it hard to grow its domain schema and run arbitrary queries.
Our short-term goal is to build a system that, as the basis for a User Agent Service, can support multiple [Tofino](https://github.com/mozilla/tofino) UX experiments without having a storage engineer do significant data migration, schema work, or revving of special-purpose endpoints.
## Comparison to DataScript
DataScript asks the question: "What if creating a database would be as cheap as creating a Hashmap?"
Datomish is not interested in that. Instead, it's strongly interested in persistence and performance, with very little interest in immutable databases/databases as values or throwaway use.
One might say that Datomish's question is: "What if an SQLite database could store arbitrary relations, for arbitrary consumers, without them having to coordinate an up-front storage-level schema?"
(Note that [domain-level schemas are very valuable](http://martinfowler.com/articles/schemaless/).)
Another possible question would be: "What if we could bake some of the concepts of CQRS and event sourcing into a persistent relational store, such that the transaction log itself were of value to queries?"
Some thought has been given to how databases as values — long-term references to a snapshot of the store at an instant in time — could work in this model. It's not impossible; it simply has different performance characteristics.
Just like DataScript, Datomish speaks Datalog for querying and takes additions and retractions as input to a transaction. Unlike DataScript, Datomish's API is asynchronous.
Unlike DataScript, Datomish exposes free-text indexing, thanks to SQLite.
## Comparison to Datomic
Datomic is a server-side, enterprise-grade data storage system. Datomic has a beautiful conceptual model. It's intended to be backed by a storage cluster, in which it keeps index chunks forever. Index chunks are replicated to peers, allowing it to run queries at the edges. Writes are serialized through a transactor.
Many of these design decisions are inapplicable to deployed desktop software; indeed, the use of multiple JVM processes makes Datomic's use in a small desktop app, or a mobile device, prohibitive.
Datomish is designed for embedding, initially in an Electron app ([Tofino](https://github.com/mozilla/tofino)). It is less concerned with exposing consistent database states outside transaction boundaries, because that's less important here, and dropping some of these requirements allows us to leverage SQLite itself.
SQLite is a traditional SQL database in most respects: schemas conflate semantic, structural, and datatype concerns; the main interface with the database is human-first textual queries; sparse and graph-structured data are 'unnatural', if not always inefficient; experimenting with and evolving data models are error-prone and complicated activities; and so on.
Datomish aims to offer many of the advantages of SQLite — single-file use, embeddability, and good performance —while building a more relaxed and expressive data model on top.
Many thanks to ([David Nolen](https://github.com/swannodette)) and ([Nikita Prokopov](https://github.com/tonsky)) for demonstrating how to package ClojureScript for distribution via npm.
