作者Bting (鸡农鸡舍捡鸡蛋)
看板Database
标题[请益]Relational model
时间Sat Jan 31 14:48:40 2009
各位大大好
小弟在学习database processing (David M.Kroenke)
一些课後作业有些不了解的地方 请各位大大解惑 谢谢
题目是这样的
SHIPMENT (ShipmentNumber, VendorName, VendorContact, VendorFax, DepartureDate,
ArrivalDate, CountryOfOrigin, Destination, ShipmentCost, InsuranceValue,
Insurer)
(因为没有给实际的table 所以无法确切知道各column之间的关系)
1.Write a funcitional dependency that express the fact that
the cost of a shipment between two cities is always the same.
这题小弟应该没想错 (CountryOfOrigin, Destination)->ShipmentCost
之後就很不能理解了
2.Write a fun~ dependency that express ~
the insurance value is always the same for a given vendor
3.~
the insurance value is always the same for a given vendor and Country of Origin
小弟的想法是这样
ShipmentNumber->(VendorName,DepartureDate,ArrivalDate,Destination, Insurer)
VendorName->(VendorContact, VendorFax,CountryOfOrigin)
(CountryOfOrigin,Destination)->ShipmentCost
(ShipmentCost,Insurer)->InsuranceValue
请问各位 小弟这样有没有错误
如果没有问题的话 要往哪方面才能找出2 3 的答案呢 ?
谢谢
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