Database Reference
In-Depth Information
PERSON50 is a subset of
P
and contains only those tuples of
P
that represent information
about the 50-year old people in that society.
It is very easy to show relations in a tabular form as shown in following figure. Each row of
the table acts as distinct tuple, so that its degree is a number of columns and its cardinality
is a number of rows in the table. The attribute names may not be the same as the names
of their underlying domains. In a relation, no two tuples can be identical and the order in
which the tuples appear is not significant. The values in the relations will thus be referred to
through a combination of a relation name and the attribute name. Tuples are solely identi-
fied through the attribute values in the relational model. An attribute (or a set of attributes)
uniquely identify any particular tuple within a relation.
Because the idea of a relation is modeled on a mathematical construct, a relation is a table
which obeys a certain restricted set of rules:
Every relation in a database must have a unique name
