Basic Structure Formally, given sets D,, D2, .. D, a relation r is a subset of D X D,x.X Thus a relation is a set of n-tuples(a1, a2,..., an)where each a;∈D Example: if customer-name= Jones, Smith, Curry, Lindsay! customer-street= Main, North, Park Then r=[ (Jones, Main, Harrison,'A customer-city Harrison, Rye ittsfieldy (Smith, North, Rye (Curry, North, Rye) (Lindsay, Park, Pittsfield)y is a relation over customer-name x customer-street X customer-city Database System Concepts 3.3 OSilberschatz, Korth and SudarshanDatabase System Concepts 3.3 ©Silberschatz, Korth and Sudarshan Basic Structure Formally, given sets D1 , D2 , …. Dn a relation r is a subset of D1 x D2 x … x Dn Thus a relation is a set of n-tuples (a1 , a2 , …, an ) where each ai  Di Example: if customer-name = {Jones, Smith, Curry, Lindsay} customer-street = {Main, North, Park} customer-city = {Harrison, Rye, Pittsfield} Then r = { (Jones, Main, Harrison), (Smith, North, Rye), (Curry, North, Rye), (Lindsay, Park, Pittsfield)} is a relation over customer-name x customer-street x customer-city