<Tr> <Td> View or result set </Td> <Td> Derived relvar </Td> <Td> Any set of tuples; a data report from the RDBMS in response to a query </Td> </Tr> <P> 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 . </P> <P> 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 . </P> <P> Tuples by definition are unique . If the tuple contains a candidate or primary key then obviously it is unique; however, a primary key need not be defined for a row or record to be a tuple . The definition of a tuple requires that it be unique, but does not require a primary key to be defined . Because a tuple is unique, its attributes by definition constitute a superkey . </P>

Domain of a column in relational database design in sql server