fluidb/README.md

cozo

A general-purpose, transactional, relational database that uses Datalog for query, is embeddable but can also handle huge amounts of data and concurrency, and focuses on graph data and algorithms.

What does embeddable mean here?

A database is almost surely embedded if you can use it on a phone which never connects to any network (this situation is not as unusual as you might think). SQLite is embedded. MySQL/Postgres/Oracle are client-server.

A database is embedded if it runs in the same process as your main program. This is in contradistinction to client-server databases, where your program connects to a database server (maybe running on a separate machine) via a client library. Embedded databases generally require no setup and can be used in far more environments.

We say Cozo is embeddable instead of embedded since you can also use it in client-server mode, which can make better use of server resources and allow much more concurrency than in embedded mode.

Why graphs?

Because data are inherently interconnected. Most insights about data can only be obtained if you take this interconnectedness into account.

Most existing graph databases start by requiring you to shoehorn your data into the labelled-property graph model. We don't go this route because we think the traditional relational model is much easier to work with for storing data, much more versatile, and can deal with graph data just fine. Even more importantly, the most piercing insights about data usually come from graph structures implicit several levels deep in your data. The relational model, being an algebra, can deal with it just fine. The property graph model, not so much, since that model is not very composable.

What is so cool about Datalog?

Datalog can express all relational queries. Recursion in Datalog is much easier to express, much more powerful, and usually runs faster than in SQL. Datalog is also extremely composable: you can build your queries piece by piece.

Recursion is especially important for graph queries. Cozo's dialect of Datalog supercharges it even further by allowing recursion through a safe subset of aggregations, and by providing extremely efficient canned algorithms (such as PageRank) for the kinds of recursions frequently required in graph analysis.

As you learn Datalog, you will discover that the rules of Datalog are like functions in a programming language. Rules are composable, and decomposing a query into rules can make it clearer and more maintainable, with no loss in efficiency. This is unlike the monolithic approach taken by the SQL select-from-where in nested forms, which can sometimes read like golfing.

Getting started

Usually, to learn a database, you need to install it first. This is unnecessary for Cozo as a testimony to its extreme embeddability, since you can run a complete Cozo instance in your browser, at near-native speed for most operations!

So open up the Cozo in WASM page, and then:

• Follow the tutorial to learn the basics;
• read the manual for the finer points.

After you have decided that Cozo is worth experimenting with for your next project, you can scroll down to learn how to use it embedded (or not) in your favourite environment.

Teasers

If you are in a hurry and just want a taste of what querying with Cozo is like, here it is. In the following *route is a relation with two columns fr and to, representing a route between those airports, and FRA is the code for Frankfurt Airport.

How many airports are directly connected to FRA?

?[count_unique(to)] := *route{fr: 'FRA', to}

count_unique(to)
310

How many airports are reachable from FRA by one stop?

?[count_unique(to)] := *route{fr: 'FRA', to: 'stop},
                       *route{fr: stop, to}

count_unique(to)
2222

How many airports are reachable from FRA by any number of stops?

count_unique(to)
3462

What are the two most difficult-to-reach airports by the minimum number of hops required, starting from FRA?

reachable[to] := *route{fr: 'FRA', to}
reachable[to] := reachable[stop], *route{fr: stop, to}
?[count_unique(to)] := reachable[to]

shortest_paths[to, shortest(path)] := *route{fr: 'FRA', to},
                                      path = ['FRA', to]
shortest_paths[to, shortest(path)] := shortest_paths[stop, prev_path],
                                      *route{fr: stop, to},
                                      path = append(prev_path, to)
?[to, path, p_len] := shortest_paths[to, path], p_len = length(path)

:order -p_len
:limit 2

to	path	p_len
YPO	["FRA","YYZ","YTS","YMO","YFA","ZKE","YAT","YPO"]	8
BVI	["FRA","AUH","BNE","ISA","BQL","BEU","BVI"]	7

What is the shortest path between FRA and YPO, by actual distance travelled?

start[] <- [['FRA']]
end[] <- [['YPO]]
?[src, dst, distance, path] <~ ShortestPathDijkstra(*route[], start[], end[])

src	dst	distance	path
FRA	YPO	4544.0	["FRA","YUL","YVO","YKQ","YMO","YFA","ZKE","YAT","YPO"]

Cozo attempts to provide nice error messages when you make mistakes:

?[x, Y] := x = 1, y = x + 1

eval::unbound_symb_in_head

  × Symbol 'Y' in rule head is unbound
   ╭────
 1 │ ?[x, Y] := x = 1, y = x + 1
   ·      ─
   ╰────
  help: Note that symbols occurring only in negated positions are not considered bound

Install

We suggest that you try out Cozo before you install it in your environment.

How you install Cozo depends on which environment you want to use it in. Follow the links in the table below:

Language/Environment	Official platform support	Storage
Python	Linux (x86_64), Mac (ARM64, x86_64), Windows (x86_64)	MQR
NodeJS	Linux (x86_64, ARM64), Mac (ARM64, x86_64), Windows (x86_64)	MQR
Web browser	Modern browsers supporting web assembly	M
Java (JVM)	Linux (x86_64), Mac (ARM64, x86_64), Windows (x86_64)	MQR
Clojure (JVM)	Linux (x86_64), Mac (ARM64, x86_64), Windows (x86_64)	MQR
Android	Android (ARM64, ARMv7, x86_64, x86)	MQ
iOS/MacOS (Swift)	iOS (ARM64, simulators), Mac (ARM64, x86_64)	MQ
Rust	Source only, usable on any platform with std support	MQRST
Golang	Linux (x86_64, ARM64), Mac (ARM64, x86_64), Windows (x86_64)	MQR
C/C++/language with C FFI	Linux (x86_64, ARM64), Mac (ARM64, x86_64), Windows (x86_64)	MQR
Standalone HTTP server	Linux (x86_64, ARM64), Mac (ARM64, x86_64), Windows (x86_64)	MQRST

For the storage column:

• M: in-memory, non-persistent backend
• Q: SQLite storage backend
• R: RocksDB storage backend
• S: Sled storage backend
• T: TiKV distributed storage backend

The Rust doc has some tips on choosing storage, which is helpful even if you are not using Rust. Even if a storage/platform is not officially supported, you can still try to compile your version to use, maybe with some tweaks in the code.

Architecture

Status of the project

Cozo is very young and not production-ready yet, but we encourage you to try it out for your use case. Any feedback is welcome.

Versions before 1.0 do not promise syntax/API stability or storage compatibility.

Licensing

This project is licensed under MPL-2.0 or later. See here if you are interested in contributing to the project.