Learning Relational Algebra by Snapping Blocks

Jason Gorman, Sebastian Gsell, Chris Mayfield

Department of Computer ScienceJames Madison University

SIGCSE 2014

What is an algebra?

Mathematical system consisting of:

I Operands: variables or values from whichnew values can be constructed

I Operators: symbols denoting proceduresthat construct the new values

These building blocks form expressions

What are some examples from arithmetic?

I [(x + 7)/(y − 3)] + x

What are some examples from set theory?

I R − (S ∪ T )

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Overview of relational algebra

Formal notation for specifying queries

I DBMS translates SQL into relational algebra

Operands:

I Relations

I Constants (finite relations)

Operators:

I Set operations (union, intersection, difference)

I Selection and projection (remove tuples/attributes)

I Cartesian product and join (combine tuples)

I Renaming (change schema / copy relation)

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Combining operations to form queries

Linear notation:

πtitle,year

(σlength≥100(Movies) ∩ σstudioName=‘Fox ′(Movies)

)Expression tree:

πtitle,year

∩

σlength≥100

Movies

σstudioName=‘Fox ′

Movies

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PROBLEM

How do we make theory more hands-on?

Tools of the trade

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Block based environments

Advantages [Maloney et al. 2010]

I Simplify the programming environment

I Encourage self-directed learning

I Making program execution visual

I Eliminating syntax error messages

I Making variables/data more concrete

Programming focus

I Object-oriented design

I Interactive media

I Simulation and games

I Mobile development

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MAIN IDEA

Block environment for manipulating data!

Standing on the shoulders of . . .

Features

I Free and open source (AGPL 3.0)

I Works in the browser (JavaScript)

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A quick tour of Bags

http://bags.cs.jmu.edu/

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Bags architecture

Bags (blocks, gui, results)

Snap (blocks, gui, threads)

Morphic (canvas, framework)

JavaScript (dom, runtime)

Implemented via change sets

I See the paper for details

I Special thanks to Snap!

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Moving forward

Additional features

I Bring your own data

I Load/save projects

I From blocks to Greek

Teaching materials

I Exercises and activities

I Scavenger hunt projects

Educational research

I Bags in DB courses

I Bags in CS0 / K-12

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Summary

Bags allows you to

I manipulate data sets interactively

I experiment with relational operators

I practice computational thinking

I visualize mathematical concepts

Invitation: Build your own Bags!

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