fluidb/IN_PROG.md

cozo

A general-purpose, transactional, relational database that uses Datalog for queries and has a focus on graph data.

Features

• Relational database with Datalog as the query language
• Supports recursion, including recursion through (safe) aggregation, capable of expressing complex graph operations and algorithms
• Fixed rules providing efficient whole-graph algorithms which integrate seamlessly with Datalog
• Rich set of built-in functions and aggregations
• Only a single executable, trivial to deploy and run
• Easy to use from any programming language
• Special support for Jupyter notebooks, integrate nicely with the Python DataScience ecosystem
• Modern, clean, flexible syntax, nice error messages

Teasers

In the following, :route refers to a relation with two columns named src and dst, representing routes between airports.

Find airports reachable by one stop from Frankfurt Airport (FRA), the busiest airport in the world:

?[dst] := :route{src: 'FRA', dst: stop}, 
          :route{src: stop, dst}

Find all airports reachable from Frankfurt (i.e., the transitive closure):

reachable[dst] := :route{src: 'FRA', dst}
reachable[dst] := reachable[src], :route{src, dst}
?[airport] := reachable[airport]

Compute the shortest path between Frankfurt and all airports in the world with recursion through aggregation:

shortest_paths[dst, shortest(path)] := :route{src: 'FRA', dst},
                                       path = ['FRA', dst]
shortest_paths[dst, shortest(path)] := shortest_paths[stop, prev_path], 
                                       :route{src: stop, dst},
                                       path = append(prev_path, dst)
?[dst, path] := shortest_paths[dst, path]

Use a fixed rule to compute the shortest path:

starting[airport] := airport = 'FRA'
?[src, dst, cost, path] <~ ShortestPathDijkstra(:route[], starting[])

Learning Cozo

• Start with the Tutorial to learn the basics.
• Continue with the Manual to understand the fine points.

Use cases

Even though Cozo is a general purpose database and in principle can replace established, well-tested solutions such as PostgreSQL and SQLite, that's not our intention when we wrote Cozo, nor do we recommend it if the established solutions already solve all your problems well. Instead, we have specific use cases that the traditional databases do not provide a sufficient solution.

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. We promise that when you try to open database files created with an incompatible version, Cozo will at least refuse to start instead of silently corrupting your data.

Plans for development

In the near term, before we reach version 1.0:

• Backup/restore functionality
• Many, many more tests to ensure correctness
• Benchmarks

Further down the road:

• More tuning options
• Extension system
  • The core of Cozo should be kept small at all times. Additional functionalities should be in extensions for the user to choose from.
  • What can be extended: datatypes, functions, aggregations, and fixed algorithms.
  • Extensions should be written in a compiled language such as Rust or C++ and compiled into a dynamic library, to be loaded by Cozo at runtime.
  • There will probably be a few "official" extension bundles, such as
    • arbitrary precision arithmetic
    • full-text "indexing" and searching
    • relations that can emulate spatial and other types of non-lexicographic indices
    • reading from external databases directly
    • more exotic graph algorithms

Ideas and discussions are welcome.

Cozo's storage engine

Cozo is written in Rust, with RocksDB as the storage engine. We manually wrote the C++/Rust bindings for RocksDB with cxx. Outside the storage layer, Cozo is 100% safe rust.

Licensing

The original contents of this project are licensed under AGPL-3.0 or later, with the following exceptions:

• Original contents in the cozorocks directory are licensed under MIT, or Apache-2.0, or BSD-3-Clause;
• Original contents in the docs directory are licensed under CC BY-SA 4.0.