An important
*motivation*
for studying relations and relational algebra
is that these formal concepts underly the organization and
manipulation of data in databases.
In fact, most databases are more accurately called
*relational databases* precisely because the database
is used to access relations.

In the *relational data model*,
information is stored in tables
(i.e., *relations*),
where the columns are associated with attributes and the
rows contain the values for each attribute.

Information can be added, deleted, or retrieved from a relation
using a standard set of
operations on relations, however
the real power of relations comes about from
*operations that span relations*.

An important use of the relational data model is in
*database design*,
where we must choose an appropriate collection of relations,
and implement operations on those relations efficiently.

Database queries can be expressed as operations in a
*relational algebra*, where
*algebraic laws*
of relational algebra are used to simplify queries,
and thereby optimize the implementation of database operations.

last modified Jan 21 1996 / Tom LeBlanc / leblanc@cs.rochester.edu