Basic Structure Formally,given sets D,D2,...D a relation ris a subset of D x D2 X ..X Dn Thus,a relation is a set of n-tuples(a,a2,...a)where each aie D Example:If customer_name {Jones,Smith,Curry,Lindsay,...} /Set of all customer names * customer street {Main,North,Park,...}/set of all street names*/ customer_city ={Harrison,Rye,Pittsfield,...}/set of all city names * 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 Database System Concepts-5th Edition,Oct 5,2006 2.4 ©Silberschat乜，Korth and SudarshanDatabase System Concepts - 5 2.4 ©Silberschatz, Korth and Sudarshan th Edition, Oct 5, 2006 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, …} /* Set of all customer names */ customer_street = {Main, North, Park, …} /* set of all street names*/ customer_city = {Harrison, Rye, Pittsfield, …} /* set of all city names */ 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