Datomish

Datomish is a persistent, embedded knowledge base. It's written in ClojureScript, and draws heavily on DataScript and Datomic.

Note that at time of writing, there's nothing here.

Motivation

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 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.)

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). 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.

Comparison to SQLite

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.

Contributing

Please note that this project is released with a Contributor Code of Conduct. By participating in this project you agree to abide by its terms.

See CONTRIBUTING.md for further notes.

This project is very new, so we'll probably revise these guidelines. Please comment on a bug before putting significant effort in if you'd like to contribute.

License

At present this code is licensed under MPLv2.0. That license is subject to change prior to external contributions.

SQLite dependencies

Datomish uses partial indices, which are available in SQLite 3.8.0 and higher.

It also uses FTS4, which is a compile time option.

Running a REPL

Prep

You'll need Leiningen.

# If you use nvm.
nvm use 6

lein deps
npm install

# If you want a decent REPL.
brew install rlwrap

Run lein cljsbuild auto advanced to generate JavaScript into target/.

Starting a ClojureScript REPL from the terminal

rlwrap lein run -m clojure.main repl.clj

Connecting to a ClojureScript environment from Vim

You'll need vim-fireplace. Install using Pathogen.

First, start a Clojure REPL with an nREPL server. Then load our ClojureScript REPL and dependencies. Finally, connect to it from Vim.

$ lein repl
nREPL server started on port 62385 on host 127.0.0.1 - nrepl://127.0.0.1:62385
REPL-y 0.3.7, nREPL 0.2.10
Clojure 1.8.0
Java HotSpot(TM) 64-Bit Server VM 1.8.0_60-b27
    Docs: (doc function-name-here)
          (find-doc "part-of-name-here")
  Source: (source function-name-here)
 Javadoc: (javadoc java-object-or-class-here)
    Exit: Control+D or (exit) or (quit)
 Results: Stored in vars *1, *2, *3, an exception in *e

user=> (load-file "repl.clj")
Reading analysis cache for jar:file:/Users/rnewman/.m2/repository/org/clojure/clojurescript/1.9.89/clojurescript-1.9.89.jar!/cljs/core.cljs
Compiling out/cljs/nodejs.cljs
Compiling src/datomish/sqlite.cljs
Compiling src/datomish/core.cljs
ClojureScript Node.js REPL server listening on 57134
Watch compilation log available at: out/watch.log
To quit, type: :cljs/quit
cljs.user=>

in Vim, in the working directory:

:Piggieback (cljs.repl.node/repl-env)

Now you can use :Eval, cqc, and friends to evaluate code. Fireplace should connect automatically, but if it doesn't:

:Connect nrepl://localhost:62385

To run the ClojureScript tests

Run lein doo node test once, or lein doo node to re-run on file changes.

Preparing an NPM release

The intention is that the release-js/ directory is roughly the shape of an npm-ready JavaScript package.

To generate a require/import-ready release-js/datomish.js, run

lein cljsbuild once release

To verify that importing into Node.js succeeds, run

node release-js/test

Many thanks to (David Nolen) and (Nikita Prokopov) for demonstrating how to package ClojureScript for distribution via npm.