by jj2739


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Schema
Complete description of structures of relational database. Relation names, attribute names, domains.
Selection
Selects rows (tuples) that satisfy selection condition

No duplicates

Schema of results identifcal to schema of input relation
Projection
Deletes attributes that are not in projection list

Schema of result contains exactly the fields in the projection list, with the same names that they had in the input relation

Duplicates are eliminated
Super Keys
A set of attributes that contains a key, aka a "superset of a key. Every key is a super-key", yet some super-keys are not (minimal) keys.
Keys
Closure that give you all the tuples
Bags
A bag (or multi-set) is like a set, but an element may appear more than once. e.g.     {1, 3, 1, 2} is a bag {1, 2, 3} is a bag that happens to be a set
x of y cards