數(shù)據(jù)庫系統(tǒng)基礎(chǔ)教程第四章答案-資料下載頁
2025-06-26 20:46本頁面
【正文】 ring name。relationship Courses offers inverse Courses::offeredBy。}。class Courses(key (number,offeredBy)) {attribute string number。relationship Departments offeredBy inverse Departments::offers。}。b)class Leagues (key (name)) {attribute name。relationship Teams contains inverse Teams::belongs。}。class Teams(key (name,belongs)) {attribute name,relationship Leagues belongs inverse Leagues::contains。relationship Players play inverse Players::plays。 }。class Players (key(number,plays)) {attribute number,relationship Teams plays inverse Teams::play。 }。 class Students (key ) { attribute string 。 attribute string name。 relationship Courses isTA inverse Courses::TA。 relationship Courses Takes inverse Courses::TakenBy。 }。class Professors (key ) { attribute string 。 attribute string name。 relationship Departments WorksFor inverse Department::Works。 relationship Courses Teaches inverse Courses::TaughtBy。}。 class Courses (key (no,semester,section)) { attribute string no。 attribute string semester。 attribute string section。 relationship Students TA inverse Students::isTA。 relationship Students TakenBy inverse Students::Takes。 relationship Professors TaughtBy inverse Professors::Teaches。 relationship Departments OfferedBy inverse Departments::Offer。}。class Departments (key name) { attribute name。 relationship Courses Offer inverse Courses::OfferedBy。 relationship Professors Works inverse Professors::WorksFor。}。A relationship is its own inverse when for every attribute pair in the relationship, the inverse pair also exists. A relation with such a relationship is called symmetric in set theory. . A relationship called SiblingOf in Person relation is its own inverse.a)Customers(ssNo,name,addr,phone)Account(number,type,balance)Owns(ssNo,accountNumber)b)Accounts(number,balance,type,owningCustomerssNo)Customers(ssNo,name)Addresses(ownerssNo,street,state,city)Phones(ownerssNo,street,state,city,phonearea,phoneno)We can remove Addresses relation since its attributes are a subset of relation Phones.c)Fans(name,colors)RootedBy(fan_name,teamname)Admires(fan_name,playername)Players(name,teamname,is_captain)Teams(name)remove subset of teamcolorTeamcolors(name,colorname)Colors(colorname)d)class Person { attribute string name。 relationship Person motherOf inverse Person::childrenOfFemale。 relationship Person fatherOf inverse Person::childrenOfMale。 relationship SetPerson children inverse Person::parentsOf。 relationship SetPerson childrenOfFemale inverse Person::motherOf。 relationship SetPerson childrenOfMale inverse Person::fatherOf。 relationship SetPerson parentsOf inverse Person::children。}。Person(name,mothername,fathername)The children relationship is manymany but the information can be deduced from Person relation. Hence below relation is redundant.ParentChild(parent, child)First consider each struct as if it were an atomic value . key and value association pairs can be treated as two attributes. After applying normalization,the attributes can be replaced by the fields of the structs.(a) Struct Card { string rank, string suit }。(b) class Hand { attribute Set theHand。 }。(c) Hands(handId, rank, suit)Each tuple corresponds to one card of a hand. HandId is required key to identify a hand.(d) Hand contains an array of 5 elementsclass PokerHand{attribute Array Hand(Card card1,Card card2,Card card3,Card card4,Card card5)}PokerHandS(handId,rank1,suit1,rank2,suit2,rank3,suit3,rank4,suit4,rank5,suit5)(e) class Deal { attribute Set Struct PlayerHand { string Player, Hand theHand } theDeal。 }(f) PokerDeal consist of a player and array of five card deal.class PokerDeal{string Player,attribute Array Hand(Card card1,Card card2,Card card3,Card card4,Card card5)}(g) Above can similarly be represented by key player and a value consisting of five element array.(h) dealID is a key for Deals. Thus the relations for classes Deals and Hands are: Deals(dealID, player, handID) Hands(handID, rank, suit)A simpler relation Deals below can also represents the classes: Deals(dealID, player, rank, suit)(i)The relation Deals(dealID,card) cannot identify the hand to which a card belongs. Also two attributes are required for a card。its rank and suit. Deals(dealID, handID, rank, suit)(a) C(a, f, g)(b) C(a, f, g, count)(c) C(a, f, g, position)(d) C(a, f, g, i, j)
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