Relations or Tables
A relation is defined as a set of tuples that have the same attributes. A tuple usually represents an object and information about that object. Objects are typically physical objects or concepts. A relation is usually described as a table, which is organized into rows and columns. All the data referenced by an attribute are in the same domain and conform to the same constraints. The relational model specifies that the tuples of a relation have no specific order and that the tuples, in turn, impose no order on the attributes. Applications access data by specifying queries, which use operations such as select to identify tuples, project to identify attributes, and join to combine relations. Relations can be modified using the insert, delete, and update operators. New tuples can supply explicit values or be derived from a query. Similarly, queries identify tuples for updating or deleting. It is necessary for each tuple of a relation to be uniquely identifiable by some combination (one or more) of its attribute values. This combination is referred to as the primary key.
Read more about this topic: Relational Database
Famous quotes containing the words relations and/or tables:
“Actually, the laboring man has not leisure for a true integrity day by day; he cannot afford to sustain the manliest relations to men; his labor would be depreciated in the market.
He has no time to be anything but a machine.”
—Henry David Thoreau (1817–1862)
“Eddie Felson: Church of the Good Hustler.
Charlie: Looks more like a morgue to me. Those tables are the slabs they lay the stiffs on.
Eddie Felson: I’ll be alive when I get out, Charlie.”
—Sydney Carroll, U.S. screenwriter, and Robert Rossen. Eddie Felson (Paul Newman)