數(shù)據(jù)庫(kù)系統(tǒng)基礎(chǔ)教程第四章答案(編輯修改稿)
2025-07-23 20:46 本頁(yè)面
【文章內(nèi)容簡(jiǎn)介】 sonAddress,childName,childAddress)FatherOf(childName,childAddress,fatherName,fatherAddress)MotherOf(childName,childAddress,motherName,motherAddress)Married(husbandName,husbandAddress,wifeName,wifeAddress)The manymany ChildOf relationship again requires a relation.An entity belongs to one and only one class when using objectoriented approach. Hence, the manyone relations MotherOf and FatherOf could be added as attributes to PersonChild,PersonChildFather, and PersonChildMother relations.Similarly the Married relation can be added as attributes to PersonChildMother and PersonMother (or the corresponding father relations). (c) For the Person relation at least one of husband and wife attributes will be null.Person(personName,personAddress,fatherName,fatherAddress,motherName,motherAddresss,wifeName,wifeAddresss,husbandName,husbandAddress)ChildOf(personName,personAddress,childName,childAddress)(a)People(name,fatherName,motherName)Males(name)Females(name)Fathers(name)Mothers(name)ChildOf(personName,childName)(b)People(name)PeopleMale(name)PeopleMaleFathers(name)PeopleFemale(name)PeopleFemaleMothers(name)ChildOf(personName,childName)FatherOf(childName,fatherName)MotherOf(childName,motherName)People cannot belong to both male and female branch of the ER diagram.Moreover since an entity belongs to one and only one class when using objectoriented approach, no entity belongs to People relation.Again we could replace MotherOf and FatherOf relations by adding as attributes to PeopleMale,PeopleMaleFathers,PeopleFemale, and PeopleFemaleMothers relations.(c)People(name,fatherName,motherName)ChildOf(personName,childName)(a)Each entity set results in one relation. Thus both the minimum and maximum number of relations is e.The root relation has a attributes including k keys. Thus the minimum number of attributes is a. All other relations include the k keys from root along with their a attributes. Thus the maximum number of attributes is a+k.(b)The relation for root will have a attributes. The relation representing the whole tree will have e*a attributes.The number of relations will depend on the shape of the tree. A tree of e entities where only one child exists(say left child only) would have the minimum number of relations. Thus below figure will only contain 4 subtrees that contain root E1,E1E2,E1E2E3, and E1E2E3E4. With e entity sets, minimum e relations are possible.The maximum number of subtrees result when all the entities(except root) are at depth 1. Thus below figure will contain 8 subtrees that contain root E1,E1E2,E1E3,E1E4,E1E2E3,E1E3E4,E1E2E4,and E1E2E3E4. With e entity sets, maximum 2^(e1) relations are possible.(c)The nulls method always results in one relation and contains attributes from all e entities . e*a attributes.Summarizing for a,b, and c above。 Components Relations Min Max Min Max MethodstraightE/R a a e eobjectoriented a e*a e 2^(e1)nulls e*a e*a 1 1a)b)c)d)Males and Females subclasses are plete. Mothers and Fathers are partial. All subclasses are disjoint.We convert the ternary relationship Contracts into three binary relationships between a new entity set Contracts and existing entity sets.a)b)c)A selfassociation ParentOf for entity set people has multiplicity 0..2 at parent role end.In a Library database, if a patron can loan at most 12 books, them multiplicity is 0..12.For a FullTimeStudents entity set, a relationship of multiplicity 5..* must exist with Courses (A student must take at least5 courses to be classified FullTime.Customers(SSNo,name,addr,phone)Flights(number,day,aircraft)Bookings(row,seat,custSSNo,FlightNumber,FlightDay)Customers(SSNo,name,addr,phone)Flights(number,day,aircraft)Bookings(row,seat,custSSNo,FlightNumber,FlightDay)a)Movies(title,year,length,genre)Studios(name,address)Presidents(cert,name,address)Owns(movieTitle,movieYear,studioName)Runs(studioName,presCert)Movies(title,year,length,genre)Studios(name,address)Presidents(cert,name,address)Owns(movieTitle,movieYear,studioName)Runs(studioName,presCert)b)Since the subclasses are disjoint, Object Oriented Approach is used.The hierarchy is not plete. Hence four relations are requiredMovies(title,year,leng
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