Darwen

Darwen is an in-memory engine for relational algebra inspired by The Third Manifesto of Date, Codd, and Darwen.

This is the final version of the library. Further development is not planned, because the project is educational.

Example

use darwen::{
    heading,
    tuple,
    prelude::{AttributeName, Expression, Predicate, RelationBuilder, Scalar, ScalarType},
};

let users = RelationBuilder::new()
    .with_heading(heading!(name = ScalarType::String, age = ScalarType::Integer)?)
    .with_body(vec![
        tuple!(name = "Monica", age = 18)?,
        tuple!(name = "Erica", age = 19)?,
        tuple!(name = "Rita", age = 20)?,
        tuple!(name = "Tina", age = 21)?,
        tuple!(name = "Sandra", age = 22)?,
        tuple!(name = "Mary", age = 23)?,
        tuple!(name = "Jessica", age = 18)?,
    ])
    .build()?;

let adults = users.restrict(&Predicate::gt(
    AttributeName::from("age"),
    Scalar::Integer(20),
))?;

let expected = RelationBuilder::new()
    .with_heading(heading!(name = ScalarType::String, age = ScalarType::Integer)?)
    .with_body(vec![
        tuple!(name = "Tina", age = 21)?,
        tuple!(name = "Sandra", age = 22)?,
        tuple!(name = "Mary", age = 23)?,
    ])
    .build()?;

assert_eq!(adults, expected);
# Ok::<(), darwen::prelude::Error>(())

Implemented Operations

RESTRICT/SELECTION (σ)

Example - cargo run --example restrict

σ age > 20 (people)

people

Output

PROJECT (π)

Example - cargo run --example project

π name (people)

people

Output

RENAME (ρ)

Example - cargo run --example rename

ρ person_name/name (people)

people

Output

UNION (⋃)

Example - cargo run --example union

a ⋃ b

a

b

Output

DIFFERENCE (−)

Example - cargo run --example difference

a − b

a

b

Output

PRODUCT (×)

Example - cargo run --example product

colors × sizes

colors

sizes

Output

JOIN (⋈)

Example - cargo run --example join

users ⋈ cities

users

cities

Output

INTERSECT (∩)

Example - cargo run --example intersect

a ∩ b

a

b

Output

Sources

• The Third Manifesto - the foundational manifesto of relational databases
• TutorialD - a practical implementation of relational algebra
• BNF for TutorialD from RelDB project