156 lines
6.4 KiB
Markdown
156 lines
6.4 KiB
Markdown
# Datomish
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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).
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Note that at time of writing, there's nothing here.
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## Motivation
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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.
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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.
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## Comparison to DataScript
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DataScript asks the question: "What if creating a database would be as cheap as creating a Hashmap?"
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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.
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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?"
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(Note that [domain-level schemas are very valuable](http://martinfowler.com/articles/schemaless/).)
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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?"
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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.
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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.
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Unlike DataScript, Datomish exposes free-text indexing, thanks to SQLite.
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## Comparison to Datomic
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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.
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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.
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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.
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## Comparison to SQLite
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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.
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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.
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## Contributing
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Please note that this project is released with a Contributor Code of Conduct.
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By participating in this project you agree to abide by its terms.
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See [CONTRIBUTING.md](/CONTRIBUTING.md) for further notes.
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This project is very new, so we'll probably revise these guidelines. Please
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comment on a bug before putting significant effort in if you'd like to
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contribute.
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## License
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At present this code is licensed under MPLv2.0. That license is subject to change prior to external contributions.
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## SQLite dependencies
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Datomish uses partial indices, which are available in SQLite 3.8.0 and higher.
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It also uses FTS4, which is [a compile time option](http://www.sqlite.org/fts3.html#section_2).
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## Running a REPL
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### Prep
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You'll need [Leiningen](http://leiningen.org).
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```
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# If you use nvm.
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nvm use 6
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lein deps
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npm install
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# If you want a decent REPL.
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brew install rlwrap
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```
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Run `lein cljsbuild auto advanced` to generate JavaScript into `target/`.
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### Starting a ClojureScript REPL from the terminal
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```
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rlwrap lein run -m clojure.main repl.clj
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```
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### Connecting to a ClojureScript environment from Vim
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You'll need `vim-fireplace`. Install using Pathogen.
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First, start a Clojure REPL with an nREPL server. Then load our ClojureScript REPL and dependencies. Finally, connect to it from Vim.
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```
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$ lein repl
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nREPL server started on port 62385 on host 127.0.0.1 - nrepl://127.0.0.1:62385
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REPL-y 0.3.7, nREPL 0.2.10
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Clojure 1.8.0
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Java HotSpot(TM) 64-Bit Server VM 1.8.0_60-b27
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Docs: (doc function-name-here)
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(find-doc "part-of-name-here")
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Source: (source function-name-here)
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Javadoc: (javadoc java-object-or-class-here)
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Exit: Control+D or (exit) or (quit)
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Results: Stored in vars *1, *2, *3, an exception in *e
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user=> (load-file "repl.clj")
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Reading analysis cache for jar:file:/Users/rnewman/.m2/repository/org/clojure/clojurescript/1.9.89/clojurescript-1.9.89.jar!/cljs/core.cljs
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Compiling out/cljs/nodejs.cljs
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Compiling src/datomish/sqlite.cljs
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Compiling src/datomish/core.cljs
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ClojureScript Node.js REPL server listening on 57134
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Watch compilation log available at: out/watch.log
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To quit, type: :cljs/quit
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cljs.user=>
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```
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in Vim, in the working directory:
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```
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:Piggieback (cljs.repl.node/repl-env)
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```
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Now you can use `:Eval`, `cqc`, and friends to evaluate code. Fireplace should connect automatically, but if it doesn't:
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```
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:Connect nrepl://localhost:62385
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```
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## To run the ClojureScript tests
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Run `lein doo node test once`, or `lein doo node` to re-run on file changes.
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### Preparing an NPM release
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The intention is that the `release-js/` directory is roughly the shape of an npm-ready JavaScript package.
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To generate a require/import-ready `release-js/datomish.js`, run
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```
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lein cljsbuild once release
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```
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To verify that importing into Node.js succeeds, run
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```
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node release-js/test
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```
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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.
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