RelAlg.js - A JavaScript Relational Algebra evaluator

This Relational Algebra evaluator is written by me, Morten Fangel ([email protected], twitter.com/fangel). For their assistance with this project, I'd like to thank Assistant Professor, Ph.D. Henrik Bulskov from Roskilde University and Associate Professor Philippe Bonnet, IT University of Copenhagen.

Feel free to contact me if you have any issues or ideas for further work.

Usage

RelAlg.js is now in version 0.2.0, and consists of a web-application and a command-line interface. The web-application can be seen at http://fangel.github.io/RelAlg.js, and the CLI can be installed using npm install relalg.js.

RelAlg.js consists of a main library (lib/relalg) that contains a parser, a static type-checker and a evaluation tool. Then a Boostrap/Flight powered web-application (lib/relalg/web) and a Node.js REPL-style CLI (lib/relalg/cli).

All the available functions takes input like this Operation[arguments](Relation). Binary operations are preformed using Relation1 Operation Relation2.

Features of the CLI REPL

The REPL is built on top of Node.js, so you can use the special Node.js commands. The two most useful are .save and .load.
.save [filename] will simply take all the operations you have performed in the current session and save them to a file with the name filename.
.load [filename] will read in the file specified by filename and run the commands, one line at a time.

This enables you to have a file that defines a set of operations that you can start all your sessions out by loading them. In the future I will probably add a command-line parameter to a file with initial relations, but till then, the .save and .load will have to do.

Operations

Relations

You can either reference a relation by it's name (if you have previously assigned a relation), or you can create anonymous relations with the syntax

[['attribute_a', 'attribute_b'] -> [1,2], [2,3], [3,4]]

Projection

Projections are done via the Project operation. And example where the columns a and b are projected would be

Project[a,b]( Relation )

Renaming

Renaming are done with the Rename operation. If you want to rename the attribute alpha into a the command would be

Rename[alpha/a]( Relation )

Selection

Selection are done with the Select operation. It takes a boolean expression as its arguments, ie

Select[a == 2 && b <= 3]( Relation )

And and or are expressed with && and ||. The supported comparison operations are:

• == (equals)
• != (not equals)
• <= (less than or equals)
• < (less than)
• >= (greater than or equals)
• > (greater than)

Strings are represented quoted in '-s, ie 'this is a string'. If you want to use '-s inside your string, escape them by adding an extra ', ie 'it''s doubles all the way'.

Union

Unions are made using the Union binary operation. Note that the two relations must have the same attributes, NOTE: in the same order!.
Example:

Relation1 Union Relation2

Intersection

Intersections are calculated with the Intersect binary operations. Note that the two relations must have the same attributes, NOTE: in the same order!.
Example:

Relation1 Intersection Relation2

Set difference

Set differences are calculated using the - binary operations. Note that the two relations must have the same attributes, NOTE: in the same order!.
Example:

Relation1 - Relation2

Cartesian product (Cross-product)

The Cartesian product of two relations is created with the X binary operator.
Example:

Relation1 X Relation2

Warning: If the two relations both have an attribute with the same name, there is a naming conflict. This will cause the calculations to fail. You must ensure no duplicate attributes.

Joins

Joins are created using the Join binary operation.

Theta-joins (conditional joins)

If you wish to create a theta-join, you provide the join-condition like this:

Relation1 Join[attribute1 == attribute2] Relation2

Warning: If both relations have attributes with the same name, the calculation will fail. If your intention was to join on the attributes, use a Natural Join. If your intent wasn't to join on those conditions, you must rename the attributes for at least one of the relations.

There is no specific notation for creating Equi-joins, just create a all-AND, all-equality condition and your Theta-join will classify as a Equi-join.

Natural-join

If you do not give a condition as an argument to the Join operator, it will be treated as a natural join. In other words, natural joins are created like this:

Relation1 Join Relation2

Division

The standard operator for divisions (/) is used to calculate the division between two relations. An example would be

Relation1 / Relation2

Extending the grammar

The lexer/parse is built using Jison. So to extend the grammer, you need to have it installed. When Jison and Grunt is installed, you can rebuild the parser from the grammar-file (src/relalg.jison), using grunt build.