上海财经大学数据库系统课程考试卷(A)2 ０ 05——２０ 06 年第二学期姓名学号班级得分1. True or Fals ｅ. (20 p ｏ in ｔｓ)1). Ｅ xternal／Conceptual Mapping ｉ s th ｅ key to physical da ｔa indepe ｎ d ｅ nce. 2). DA is ｔ h ｅ ｐｅ rson who ｐ rovides the neces ｓａ ry te ｃ hn ｉca ｌ s ｕ p ｐｏ rt ｆ or impl ｅｍｅ nti ｎ g ｔｈ o ｓ e ｄecisions. 3). It is ｔ he ｊ o ｂ of t ｈ e ＤＭ L p ｒ oc ｅｓ sor to ｃ h ｏ o ｓ e ａ n ｅ ffic ｉ ent wa ｙ ｔ o ｉｍ plemen ｔ use ｒ’ｓ re ｑ uest.4)． Ｒ ela ｔ io ｎａ l ｄ a ｔａ model rep ｒ ese ｎ t ｓ t ｈ e data ｉ n ａ ｄ at ａ base as a co ｌ le ｃｔ io ｎ o ｆ t ａ bles.5)． Ｉ ndexe ｓ al ｌ ow t ｈｅ ｄａ taba ｓ e man ａ gem ｅ nt sy ｓt ｅｍ t ｏ directly a ｃ c ｅ s ｓ the ｒ ows of ｔ he ｔａｂ l ｅ oｎ which th ｅ index has b ｅｅ n ｄ e ｆ ined.６）. Si ｎｃ e ｔｈ e l ｏ gical d ａｔａ struct ｕ r ｅ s a ｒ e i ｎｔended fo ｒ th ｅ ａ ppl ｉ ca ｔ ion progr ａ m ｍ er ｓ, the data ｂａs ｅ ｄ es ｉ gner is not involved in their d ｅｖｅｌ opment. 7）． Ｖｉ ews ａ re only desc ｒ iptio ｎ s of data. They ar ｅ not re ａｌ ｔ ab ｌ es．8). D ｅ n ｏ r ｍａ l ｉ zat ｉ on cau ｓｅ s ｔ he ｒ edund ａ nt st ｏrag ｅ ｏ f i ｎ for ｍ ation． ９). Ｈ oriz ｏ nta ｌ splittin ｇ of a relati ｏｎａｌ v ａｒ iable always create ｓ r ｅ l ａ t ｉ o ｎ al va ｒ iabl ｅ s fo ｒ different primary key rang ｅ s o ｆ the ｏｒ ig ｉ nal ｒｅｌ ation ａｌ v ａ ri ａ ble． 10).For ａ n ｕ nord ｅ red r ｅｔｒ ieval re ｑ ues ｔ, diff ｅ ren ｔ executions of t ｈｅ ｒ equ ｅ st may re ｔ urn t ｈ e r ｅ trieved rows in ａ d ｉ...
