introduction to databases in this diagram there is table called studentsit is being used to hold information about students attending meeting the table has attributes (or columnsdefined for idnamesurnamesubject and email in this casethe id is probably what is known as primary key the primary key is property that is used to uniquely identify the student rowit cannot be omitted and must be unique (within the tableobviously names and subjects may well be duplicated as there may be more than one student studying animation or games and students may have the same first name or surname it is probable that the email column is also unique as students probably don' share an email address but again this may not necessarily be the case you might at this point wonder why the data in relational database is called relational and not tables or tabularthe reason is because of topic known as relational algebra that underpins relational database theory relational algebra takes its name from the mathematical concept known as relation howeverfor the purposes of this you don' need to worry about this and just need to remember that data is held in tables data relationships when the data held in one table has link or relationship to data held in another table then an index or key is used to link the values in one table to another this is illustrated below for table of addresses and table of people who live in that address this shows for examplethat 'phoebe gateslives at address 'addr which is queen streetbristolbs yy