(no subject)

[impossiblewizardry]

so

aRb means "a and b are siblings"

you can represent this relation R as a set of all pairs for which it's true

{
{ Lana Wachowski, Linda Wachowski },
{ Linda Wachowski, Lana Wachowski },
{ Joel Cohen, Ethan Cohen },
{ Ethan Cohen, Joel Cohen }
}

and this looks like a spreadsheet with two columns (a set of two rows)

so a "relational database" stores the data as a collection of spreadsheets.