2.1introduction to the relational model

2.1introduction to the relational model

structure of relational database
table
tuple
attribute
domain (allowed values)
atomic (indivisible)

instance
null

database schema
consistence
a list of attributes (unchangeable)
corresponding domains (changeable)

difference #important
schema
The schema of a relation refers to its logical design
instance
an instance of the relationreferstoitscontentsatapointintime

keys
superkey (a set of one or more attributes)
candidate keys (minimal superkeys )
primary key(denote a candidate key)

foreign key
referential integrity constraint
referencing relation(include a foreign)
referenced relation(the primary key is another relation's attributes.) 

schema diagrams
​A schema diagram is a pictorial depiction of the schema of a database that shows the relations in the database, their
attributes, and primary keys and foreign keys
procedural language
nonprocedural language

relational operations
summary