Chapter 2: Relational model Flashcards
def: attribute domain
set of allowed values of each attribute
def: atomic attribute
indivisible
def: null value
unknown
relations are unordered: true or false
true
def: database schema
logical structure of the database
def: database instance
snapshot of data at given instant in time
def: superkey
sufficient to identify a unique tuple of each relations
def: candidate key
if it is a superkey and is minimal
def: primary key
uniquely identifies tuple chose from candidate key
key: foreign key
value in one relation must appear in another relation
‘pure’ languages (3)
- relational algebra
- tuple relational calculus
- domain relational calculus
def: relational-algebra expression
composition of relational algebra operations
relational algebra operations (6)
- select
- project
- union
- set difference
- cartesian product
- rename
def: arity
same number of attributes
def: compatible
columns dealing with the same type of values
