RSS
Twitter
Facebook
Relational Database Schema: A set
S of relation schemas that belong to the same database. S is the name of the database.
S = {R1, R2, ..., Rn}
Entity Integrity: The primary key
attributes PK of each relation schema R in S cannot have null values in any
tuple of r(R). This is because primary key values are used to identify the
individual tuples.
t[PK] ¹ null for any tuple t in
r(R)
Note: Other attributes of R may
be similarly constrained to disallow null values, even though they are not
members of the primary key.
0 comments