Purpose

This package contains a Nearley-grammar for a Relational Algebra. The grammar tries to stay as close to how you would denote an expression in RA on the blackboard as possible by utilising appropriate unicode symbols.

Compiling the Grammar

The package comes with a compiled grammar located in ra.js. Utilise the nearley-compiler to create a parser from the ra.ne grammar file yourself, if need be. From within the project root:

./node_modules/nearley/bin/nearleyc.js ra.ne > ra.js

You can then include the parser and utilise it as needed. The module features the following properties:

• grammar: the raw grammar,
• compiledGrammar: the grammar compiled using nearley,
• createParser(): a function which creates a new nearley parser from the compiled grammar.

Sample Input

Just some input strings to give you a feeling for how expressions in this RA look like. The ra.ne serves as "full documentation" of expressions in this grammar.

• A ∩ B: intersection of A and B.
• A - B: A without B.
• σ{x=41+1}(A): Applying the predicate x=41+1 to all tuples in A.
• π{[a,b]}(A): Selecting only the fields a and b from the relation A.
• ρ{[x→a,y→b]}(A): Renaming the fields x and y in A to a and b respectively.

Notes to Myself

Programmatic Interface (if should ever need): https://www.npmjs.com/package/nearley-there