Data Model:

MarvelHeroes(hid, hero, realname)
DCHeroes(hid, hero, realname)
Movies(mid, moviename, year)
HeroInMovie(hid, mid)


Relational Algebra
----------------------
Set Operations:

    R Union S
    R Intersection S
    R Set Difference S

Rename: Given R(A,B,C)

   T(A1, B1, C1) = R

SELECTION

    SELECT_C R = {t in R such that t satisfies the boolean condition C}

PROJECTION

   PROJECT_{A1,...AN} (R) = {t in R but only the values for the attributes A1,...,AN}

CARTESIAN PRODUCT

Assume R and S have no common attributes

   R x S = { t such that t has all the attributes in R and all the attributes in S,
           such that there is a tuple r in R and a tuple s in S where t is equal
	   to r for attributes in R
	   and to s for attributes in S}


R(A,B) = { <a1, b1>, <a2, b1> }

S(C,D) = { <c1, d1>, <c2, d2>, <c3, d3> }

T = R x S

T(A,B,C,D) = {<a1,b1,c1,d1>, <a1,b1,c2,d2>, <a1,b1 c3,d3>,
              <a2,b1,c1,d1>, <a2,b1,c2,d2>, <a2,b1,c3,d3>}

T1(Hid1, Hero, Realname) = Marvel_Heroes

HID1	HERO	        REALNAME
------------------------------------
m1	Spiderman	Peter Parker
m2	Black Panther	T’Challa
m3	Thor	        Thor
m4	Jessica Jones	Jessica Jones
m5	Iron Man	Tony Stark


HeroInMovie

hid	Mid
-------------
d1	1
m1	2
d3	3
d4	4
d5	5
m2	6
m3	7
m3	8
m3	9
m5	9



T2 = HeroInMovie x T1

hid	Mid   HID1	HERO	        REALNAME 
-------------------------------------------------
d1	1     m1	Spiderman	Peter Parker
m1	2     m1	Spiderman	Peter Parker
d3	3     m1	Spiderman	Peter Parker
d4	4     m1	Spiderman	Peter Parker
d5	5     m1	Spiderman	Peter Parker
m2	6     m1	Spiderman	Peter Parker
m3	7     m1	Spiderman	Peter Parker
m3	8     m1	Spiderman	Peter Parker
m3	9     m1	Spiderman	Peter Parker
m5	9     m1	Spiderman	Peter Parker
d1	1     m2	Black Panther	T’Challa
m1	2     m2	Black Panther	T’Challa
d3	3     m2	Black Panther	T’Challa
d4	4     m2	Black Panther	T’Challa
d5	5     m2	Black Panther	T’Challa
m2	6     m2	Black Panther	T’Challa
m3	7     m2	Black Panther	T’Challa
m3	8     m2	Black Panther	T’Challa
m3	9     m2	Black Panther	T’Challa
m5	9     m2	Black Panther	T’Challa
d1	1     m3	Thor	        Thor
m1	2     m3	Thor	        Thor
d3	3     m3	Thor	        Thor
d4	4     m3	Thor	        Thor
d5	5     m3	Thor	        Thor
m2	6     m3	Thor	        Thor
m3	7     m3	Thor	        Thor
m3	8     m3	Thor	        Thor
m3	9     m3	Thor	        Thor
m5	9     M3	Thor	        Thor
d1	1     m4	Jessica Jones	Jessica Jones
m1	2     m4	Jessica Jones	Jessica Jones
d3	3     m4	Jessica Jones	Jessica Jones
d4	4     m4	Jessica Jones	Jessica Jones
d5	5     m4	Jessica Jones	Jessica Jones
m2	6     m4	Jessica Jones	Jessica Jones
m3	7     m4	Jessica Jones	Jessica Jones
m3	8     m4	Jessica Jones	Jessica Jones
m3	9     m4	Jessica Jones	Jessica Jones
m5	9     m4	Jessica Jones	Jessica Jones
d1	1     m5	Iron Man	Tony Stark
m1	2     m5	Iron Man	Tony Stark
d3	3     m5	Iron Man	Tony Stark
d4	4     m5	Iron Man	Tony Stark
d5	5     m5	Iron Man	Tony Stark
m2	6     m5	Iron Man	Tony Stark
m3	7     m5	Iron Man	Tony Stark
m3	8     m5	Iron Man	Tony Stark
m3	9     m5	Iron Man	Tony Stark
m5	9     m5	Iron Man	Tony Stark


Name of all marvel heroes who have been in a movie in the database!

T3 = SELECT_{hid=hid1}  ( HeroInMovie x T1 )
PROJECT_{HERO} (T3)


hid	Mid   HID1	HERO	        REALNAME 
-------------------------------------------------
m1	2     m1	Spiderman	Peter Parker
m2	6     m2	Black Panther	T’Challa
m3	7     m3	Thor	        Thor
m3	8     m3	Thor	        Thor
m3	9     m3	Thor	        Thor
m5	9     m5	Iron Man	Tony Stark

PROJECT_{HERO} (T3)


Spiderman
Black Panther
Thor
Iron Man


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

ID all movies who featured a DC comic hero


T1(hid1, hero, realname) = DC_Heroes

T2 = T1 x HeroInMovie

All movies that feature a DC comic hero

T3 = SELECT_{hid1 = hid} (T2)

T3 schema?  hid1, hero, realname, hid, mid

Results = PROJECT_{mid} (T3)

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