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 predicatex=41+1
to all tuples inA
.π{[a,b]}(A)
: Selecting only the fieldsa
andb
from the relationA
.ρ{[x→a,y→b]}(A)
: Renaming the fieldsx
andy
inA
toa
andb
respectively.
Notes to Myself
Programmatic Interface (if should ever need): https://www.npmjs.com/package/nearley-there