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InteractiveTry Bmg.js in your browserWrite relational algebra queries on your own data — no installation required.→

What is Relational Algebra? A powerful way to reason, query and transform data. Learn the fundamentals.

Use it in your projects

RubyBmgFull-featured library with SQL compilation and ActiveRecord integration.

TypeScriptBmg.jsType-safe in-memory operations for JavaScript/TypeScript projects.

Works with any data

Arrays, CSV files, JSON, Redis, SQL databases — same operations everywhere.

Ruby

# In-memory array
purchases = Bmg::Relation.new([
  { product_id: 1, quantity: 5, type: 'sale' },
  { product_id: 2, quantity: 3, type: 'sample' },
])

# Or load from CSV
purchases = Bmg.csv("purchases.csv")

# Or connect to a SQL database
purchases = Bmg.sequel(:purchases, db)

# Same operations, any source
purchases
  .restrict(Predicate.neq(:type, 'sample'))
  .summarize([:product_id], quantity: :sum)

TypeScript

// In-memory array
const purchases = Bmg([
  { product_id: 1, quantity: 5, type: 'sale' },
  { product_id: 2, quantity: 3, type: 'sample' },
])

// Same operations, full type safety
purchases
  .exclude({ type: 'sample' })
  .summarize(['product_id'], { quantity: { op: 'sum', attr: 'quantity' } })

What is it good for?

Think in relations

Relational algebra gives you a powerful mental model for data manipulation. Chain operations naturally.

Query anything

Same operations work on arrays, files, Redis, or SQL. Your code doesn’t change when your data source does.

Compose freely

Extract, reuse, and combine query fragments. Build complex transformations from simple pieces.

Drop in anywhere

Works alongside ActiveRecord, Sequel, or standalone. No framework lock-in.

SQL Compilation

When your data lives in a database, Bmg compiles your queries to efficient SQL. Currently available in Ruby — coming soon to TypeScript.

suppliers
  .restrict(Predicate.eq(:city, "Paris"))
  .join(supplies, [:sid])
  .project([:name, :qty])

SELECT DISTINCT `t2`.`qty`, `t1`.`name`
FROM `suppliers` AS 't1'
INNER JOIN `supplies` AS 't2'
  ON (`t1`.`sid` = `t2`.`sid`)
WHERE (`t1`.`city` = 'Paris')

See more in our SQL vs. Bmg cheatsheet.

Source Code

Bmg (Ruby)Bmg.js (TypeScript)This Website

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