Data Model:

MarvelHeroes(hid, hero, realname)

DCHeroes(hid, hero, realname)

Movies(mid, moviename, year)

HeroInMovie(hid, mid)


Databases:

A set of relations.



Relational Algebra
----------------------

Basic Definitions:

input: set of tuples, a relation, or two relations
Output: set of tuples


Set Compatibility:

Two relations are set compatible, if they have the same schema: the same
set of attributes


Set Operations:

R Union S
R Intersection S
R Set Difference S

are defined for two relations R and S, only if R and S are set compatible.

R Union S = { tuples t such t is either in relation R or in relation S}

R Intersection S = { tuples t such that t is in both relation R and S }

R Set Difference S = { tuples t such that t is in R but not in S }


Find all heroes in either Marvel or DC Universe

T = Marvel_Heroes union DC_Heroes


Find all heroes that are both in Marvel and DC Universes

T = Marvel_Heroes intersect DC_Heroes


Find all heroes that in the Marvel Universe but not in the DC Universe

T = Marvel_Heroes - DC_Heroes

---------------

RIN is a key. Assume that a student can be both grad and undergrad.

Ugrad(RIN, Name)

Grad(RIN, Name)


Find students who are coterm, but not have graduated with their BS

Ugrad intersect Grad

Find undergraduate students who are not coterm

Ugrad - Grad

Find graduate students who are not also undergraduates

Grad - Ugrad

Find all students in the database

Grad union Ugrad