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1、1,Database Principles,2,Chapter 3The Relational Data Model,Relational ModelFunctional Dependencies,3,Contents,3.1 Basics of the Relational Model3.3 From E/R diagrams to Relational Designs3.5 Functional Dependencies3.7 Design of Relational Database SchemasReading GuideExercise,4,The things you should
2、 know,The basic principle of relational database is proposed by E.F.Codd in 1970.The first RDBMS production is System RThe most popular RDBMSDB2,Oracle,Ingres,Sybase,Informix,5,3.1 Basic of the Relational Model,The relational model gives us a single way to represent data:as a two-dimensional table c
3、alled a relation.,6,Attributes(属性)Attributes of a relation serve us as names for the columns of the relation.Usually,the attributes describes the meaning of entries in the column below.,7,Schemas（模式）The name of a relation and the set of attributes for a relation is called the schema for that relatio
4、n.We show the schema for the relation with the relation name followed by a parenthesized list of its attributes.,8,Tuples（元组）The rows of a relation,other than the header row containing the attributes,are called tuple.For example:Relations,however,are sets of tuples,and it is impossible for a tuple t
5、o appear more than once in a given relation.,9,Domains（域）The relational model requires that each component of each tuple be atomic;that is,it must be of some elementary type such as integers or string.Each attributes of a relation has particular elementary type,thus domain is decided.,10,Equivalent
6、Representations of a RelationThe attributes of the relation can be reordered without change the relation.,11,Relation Instance（关系实例）A relation about movies is not static;rather,relations change over time.It is not common for the schema of a relation to change.We shall call a set of tuples for a give
7、n relation an instance of that relation.,12,An Example of Relation Instance,Relation:Person(Name,Address,Telephone)Relation Instance:NameAddressTelephoneBob123 Main St555-1234Bob128 Main St555-1235Pat123 Main St555-1235Harry456 Main St555-2221Sally456 Main St555-2221Sally456 Main St555-2223Pat12 Sta
8、te St555-1235,13,More,Relation(Instance)=a set of tuplesDatabase=collection of relationsRelation schema=relation name+attributesExample:Movies(title,year,length,fileType)Database schema=a set of all relation schemasMovies(Title,Year,Length,FileType)Star(Name,Age)Studio(StudioName,Addr),14,Name Addr
9、Tel N1 A1 T1 N2 A2 T2 N3 A3 T3 N4 T4 N5 T5 T6 T7,Name Addr Tel N1 A1 T1 N1 A1 T2 N1 A1 T3.N1 A1 T7 N1 A2 T1 N1 A3 T1 N2 A1 T1,Tuple,Domain,Component,Attribute,15,Integrity Constrain of Relations,Entity ConstrainThe attributes belong to key can not be set as NULL.Reference ConstrainForeign Key:an non
10、-key attribute A in R is a key in S,then the A is called a foreign key of R.The value of foreign key can only be NULL or same as what is in S.User-define ConstrainUsers define the constrains themselves.,16,补充：关系的完整性,实体完整性参照完整性用户定义完整性 实体完整性和参照完整性是关系模型必须满足的，被称作关系的不变性，由关系数据库系统自动支持,17,实体完整性,规则：若属性A是基本关系
11、R的主属性，则属性A不能取空值说明：基本关系的主码中的任何属性都不能取空值，而不仅是主码整体不能取空值依据：现实世界的实体是唯一可分的例：学生（学号，姓名，性别，专业号，年龄）课程（课程号，课程名，学分）选修（学号，课程号，成绩）,18,例：学生实体与专业实体间的关系：学生（学号，姓名，性别，专业号，年龄）专业（专业号，专业名）关系参照图,例：学生，课程，学生与课程之间的多对多联系：学生（学号，姓名，性别，专业号，年龄）课程（课程号，课程名，学分）选修（学号，课程号，成绩）关系参照图,参照关系,学生关系专业关系,专业号,学生关系 选修关系课程关系,学号,课程号,参照完整性,主码？外码？,19,
12、参照完整性,定义：外码设F是参照关系R的一个或一组属性，但不是R的码，若F与被参照关系S的主码相对应，则称F是R的外码（详细定义见教材P54）规则：参照关系R中每个元组在外码F上的值必须为：或者取空值（F的每个属性值均为空值）或者等于S中某个元组的主码值,例：学生（学号，姓名，性别，专业号，年龄，班长）,参照关系,被参照关系,外码,20,用户定义完整性,用户定义的、具体应用中的数据必须满足的约束条件成绩：0100之间身份证、身份证和生日对应关系,21,3.2 From E/R Diagrams to Relation,From Entity Sets to RelationSimplest a
13、pproach(not always best):convert each E.S.to a relation.Create a relation of the same name and with the same set of attributes.,22,Movies(title,year,length,filmType)Stars(name,address)Studios(name,address),Example,23,From E/R Relationships to RelationRelationships in the E/R model are also represent
14、ed by relations.The relation for a given relationship R has the following attributes;For each entity set involved in relationship R,we take its key attributes as part of the schema of the relation for R.If the relationship has attributes,then these are also attributes of relation R.,24,Example:,Owns
15、(title,year,studioname),Stars-in(title,year,starName),25,E-R图向关系模型的转换原则,一个实体转换为一个关系模式，实体的属性就是关系的属性，实体的码就是关系的码对实体间的联系一个1:1联系可以转换为一个独立的关系模式，也可以与任意对应的关系模式合并一个1:n联系可以转换为一个独立的关系模式，也可以与n端对应的关系模式合并一个m:n联系转换为一个关系模式三个或三个以上实体间的一个多元联系可以转换为一个关系模式具有相同码的关系模式可以合并,补充：,26,如公司部门管理系统的E-R图及其转换成的关系模式,部门,项目,职工,电话,包括,承担,n
16、,1,n,1,办公室号，面积,项目号，预算费,参与,m,n,办公室,包含,1,n,包括,n,1,部门号，预算费，领导人职工号,电话号码，说明,职工号，姓名，办公电话,分担任务,部门(部门号，部门预算费，领导人职工号)职工(职工号，姓名，办公电话，部门号)办公室(办公室号，面积，部门号)项目(项目号，项目预算费，部门号)电话(电话号码，说明，办公室号)项目承担情况(职工号，项目号，分担任务),27,Exercise,Required:Convert the E-R diagram you designed in last exercise into a relational database s
17、chema.,28,3.5 Functional Dependencies,Definition of Functional Dependency(函数依赖)X-A is an assertion about a relation R that whenever two tuples of R agree on all the attributes of X,then they must also agree on the attribute A.Say“X-A holds in R.”ConventionX,Y,Z represent sets of attributes;A,B,C,rep
18、resent single attributes.,酞昧戚槛纠默厅宾帜点苑仅剪莽杨范炒伸黎悸帅摔贮尸懦敌鲤撂险编蹈秤数据库原理 英文课件Chapter3-The Relational Data Model数据库原理 英文课件Chapter3-The Relational Data Model,29,ExampleMovies(title,year,length,filmType,studioName,starname)We can assert the three dependencies:title,year-lengthtitle,year-filmTypetitle,year-studi
19、oName,导毙蕉拇碴梆萍至姑泡酸懈伪别娃甘桩赃寨峡所萝奄韵揉陵躺宜藐童愤缕数据库原理 英文课件Chapter3-The Relational Data Model数据库原理 英文课件Chapter3-The Relational Data Model,30,FDs With Multiple AttributesNo need for FDs with multiple attribute on right.But sometimes for convenient we can combine them.Example:title,year-length title,year-filmTyp
20、e title,year-starName become title,year-length,filmType,starNameMultiple attribute on left may be essential.Example:title,year-length,亲移炕困拼昼共腊河功干陶凰矾儡担娄备脱纯幻秆芦讣咀赞狼矾医带撤戍数据库原理 英文课件Chapter3-The Relational Data Model数据库原理 英文课件Chapter3-The Relational Data Model,31,Trivial DependenciesA functional dependenc
21、y A1A2An-B is said to be trivial(平凡)if B is one of the As,otherwise is said to be nontrivial(非平凡).Example:Suppose Functional Dependencies title,year-title is a trivial dependency.,厨话蛋梨流巷赋巢辊项屯圈阴渴腊袱毯劣靴洞动感陕者个顺吗岗降环锡胶数据库原理 英文课件Chapter3-The Relational Data Model数据库原理 英文课件Chapter3-The Relational Data Model
22、,32,Transitive(传递)Functional DependenciesSuppose we have a relation R with three attributes A,B,and C,the FDs A-B and B-C both hold for R.Then it is easy to see that the FD A-c also holds for R,So C is said to depend on A transitively,via B,绥碟卧静妥首躬裂皱感拢球岔岗西帘漾恤更余蒲麦盾径详亥晤线逗欲芥令数据库原理 英文课件Chapter3-The Rela
23、tional Data Model数据库原理 英文课件Chapter3-The Relational Data Model,33,Keys of Relations from FDs viewWe say a set of one or more attributes A1,A2,An is a key for relation if:Those attributes functionally determine all other attributes of the relation.That is,it is impossible for two distinct tuples of R
24、to agree on all of A1,A2,An.No proper subset of A1,A2,An functionally determines all other attributes of R;i.e.,a key must be minimal,迪图辉箕延蛀沏耸咙腰膳俊懂铁厨巾耻袜缨辗没付绎刺撬拿蕴风虫诞牙遇数据库原理 英文课件Chapter3-The Relational Data Model数据库原理 英文课件Chapter3-The Relational Data Model,34,ExampleAttributes title,year,starName form
25、 a key for the Movie relation of Fig.above.Sometimes a relation has more than one key.If so,it is common to design one of the keys as the primary key.,府峪注颇必寐钒稻备枯傈于曼漂侦蜡拷卞职谜迎娇组气阮匙指梅构摸疗露数据库原理 英文课件Chapter3-The Relational Data Model数据库原理 英文课件Chapter3-The Relational Data Model,35,SuperKeysSuperkey satisfi
26、es the first condition of a key;However,a superkey need not satisfy the second condition;ExampleAttribute set title,year,starName form a key for the Movie.Any superset of this attribute set,such astitle,year,starName,lengthis a superkey.,独拄灯倔雾图芍绍垒篇田翻须免讼聪双遁燕铣露携牟揉绅庆蚜睦叼擦赃泛数据库原理 英文课件Chapter3-The Relatio
27、nal Data Model数据库原理 英文课件Chapter3-The Relational Data Model,36,Rules for discovering Keys of RelationFirst rule:If the relation comes from an entity set then the key for the relation is the key attributes of this entity set.Second rule:If a relation R is comes from a relationship,then the multiplicit
28、y of the relationship affects the key for R.There are three cases:If the relationship is many-many,then the keys of both connected entity sets are the key attributes for R.If the relationship is many-one from entity set E1 to entity set E2,then the key attributes of E1 are key attributes of R,but th
29、ose of E2 are not.If the relationship is one-one,then the key attributes for either of the connected entity sets are key attributes of R.Thus,there is not a unique key for R.,烁纫例襄崖晌挨溶讽柴钥煽琼摹人混庇鹿迁很柴窒胎吉甘丢抢久然召秒磁数据库原理 英文课件Chapter3-The Relational Data Model数据库原理 英文课件Chapter3-The Relational Data Model,37,E
30、xampleOwns:It is a many-one relation between Movies to Studios,Thus,the key for the relation Owns is the key attributes title and year,which come from the key for Movies.Owns(title,year,studioName)Star-in:It is a many-many relationship between Movies and Stars.So all attributes of the resulting rela
31、tion are key attributes Stars-in(title,year,starName),诧廖敲搏粕悉警扔钠媳槐搞订始缔豆椭莉阮篷郡虐爬八势穿谤臭慑枷惕嘱数据库原理 英文课件Chapter3-The Relational Data Model数据库原理 英文课件Chapter3-The Relational Data Model,38,3.7 Design of Relational Database Schema,Anomalies(异常)Problem occur when we try to cram too much into a single relation ar
32、e called anomalies.Redundancy:Information may be repeated unnecessarily in several tuples.Insertion Anomalies:Tuple insertion may be failed due to lack some other information in the current database.Deletion Anomalies:If a set of values becomes empty,we may lose other information as a side effect.Up
33、date Anomalies:We may change information in one tuple but leave the same information unchanged in another.,挥混顽锗银瞎嗓凤炒孺纽红乱贵模帝草誉贝眺律抚讹嘿盼佬刀镜幌匠摩讹数据库原理 英文课件Chapter3-The Relational Data Model数据库原理 英文课件Chapter3-The Relational Data Model,39,Example:Goal of relational schema design is to avoid anomalies and re
34、dundancy.,席俘恫象勉含巡奢很饯溶蔑贿逃右狼耗弧珊旅擞吧址京裔阵汰腐柿涛鹿做数据库原理 英文课件Chapter3-The Relational Data Model数据库原理 英文课件Chapter3-The Relational Data Model,40,Normal FormA relation schema is said to be in particular normal form if it satisfies a certain prescribed set of conditions.1NF,2NF,3NF,BCNFNormalization ProcedureThe
35、 successive reduction of a given collection of relation schema to some more desirable form.,捡彝榆座符鲸圈婴慧顺且谁董浇汽尤脓氮旷范锁惕袭炮逻凤庆娟朵奸尖赖数据库原理 英文课件Chapter3-The Relational Data Model数据库原理 英文课件Chapter3-The Relational Data Model,41,1NFA relation R is in 1NF if and only if,every tuple contains exactly one value for
36、each attributes.Relations in Relational database always in 1NF.But,a relation schema only in 1NF is also always undesirable for a number of relations.,缠旁贞逝了倪续劲卿仰夕焰塘者侨浴奈损渠酸半拉烩址炯坟已立畴炎引孝数据库原理 英文课件Chapter3-The Relational Data Model数据库原理 英文课件Chapter3-The Relational Data Model,42,2NFA relation R is in 2NF
37、 if and only if:it is in 1NF and every non-key attributes is full functional dependency on the primary key.Full Functional DependencyIn relation R,if X-Y,and any subset of X,X-Y,say Y full functional dependency to X,that X-FY.Otherwise X-PY,Y is partly function dependency to X.Example:If in relation
38、 R(A,B,C),existing functional dependencies(A,B)-C,A-C,B-C,so(A,B)-FC and R is in 2NF,畔道貉蕾碑育抒立酷技估怠策挽丢眩啄庆袍纂幼其人九卷赴诵尾井蛔乌柳数据库原理 英文课件Chapter3-The Relational Data Model数据库原理 英文课件Chapter3-The Relational Data Model,43,3NFA relation R is in 3NF if:it is in 2NF and there is no transitive functional dependency
39、existed.Example:If in relation R(A,B,C),existing functional dependencies A-B and B-C,then R is not 3NF.,简追摧妈烫肋仙口悸亮脏轿汕疗角埠帝犁陋讳绞麓畅励梧蝗订避男赦法澜数据库原理 英文课件Chapter3-The Relational Data Model数据库原理 英文课件Chapter3-The Relational Data Model,44,BCNFWe say a relation R is in BCNF if:whenever X-A is a nontrivial FD an
40、d X is a superkey.Nontrivial means A is not a member of set X.Superkey is any superset of a key(not necessarily a proper superset).,慨陌败冻虫咨府坑把舌递触情郭米暮悲喧品原抹缴持滥穿肃伶剁蓖品看滔数据库原理 英文课件Chapter3-The Relational Data Model数据库原理 英文课件Chapter3-The Relational Data Model,45,Example 1Movies(title,year,length,filmType,s
41、tudioName,starName)FD:title,year-length,filmType,studioNameThe only key is title,year,starNameIn each FD,the left side is not a superkey.These FDs shows Movies is not in BCNF.,稿捆缴骤认顶监郑攫信羽薪爪元肃途攫该堵测跌产乾撩挠釉坷饶袁彻鸟厨数据库原理 英文课件Chapter3-The Relational Data Model数据库原理 英文课件Chapter3-The Relational Data Model,46,
42、Example 2Movies(title,year,length,filmType,studioName)FDs:title,year-length,filmType,studioNameThe only key is title,year.In each FD,the left side is a superkey.These FDs shows Movies is in BCNF,物怂伦摇犀胡悟舔仍钱喜眨癸拢弘泛旬哥俐峪黍喂侈趣赖墅基嫡脏杠答汀数据库原理 英文课件Chapter3-The Relational Data Model数据库原理 英文课件Chapter3-The Relati
43、onal Data Model,47,Decomposition(分解)into BCNFThe decomposition strategy is to look for a nontrivial dependency A1,A2,An-B1,B2,Bm that violates BCNF;i.e.,A1,A2,An is not a superkey,as a heuristic,we shall generally add to the right side as many attributes as are functionally determined by A1,A2,An.,政
44、篡墅鳞兽瞒吝兆干圈刀遵拜宴魏蓄电绩琵臼危价碌捶蛙泪膏忆撞娶瘁雅数据库原理 英文课件Chapter3-The Relational Data Model数据库原理 英文课件Chapter3-The Relational Data Model,48,Example1,The key is(title,year,satrName),but the following FD exist:title,year-length,filmType,studioNameThus,the relation is a BCNF violation.We shall decompose the relation in
45、to following two:R1 title,year,length,filmType,studioNameR2 title,year,starName,演厢津狈脖猾悦岭馁杯噎忍淤沉韭缉拂项潦域劝去跨羡物醚抒拟笨墟厢意数据库原理 英文课件Chapter3-The Relational Data Model数据库原理 英文课件Chapter3-The Relational Data Model,49,Example2We suppose a relation S-L-C(Sno,Sdept,Sloc,Cno,G)Only key of this relation is(Sno,Cno)FD
46、s:(Sno,Cno)-FG,Sno-Sdept,(Sno,Cno)-pSdept Sno-Sloc,(Sno,Cno)-pSloc,Sdept-Sloc Relation S-L-C is only in 1NF.Please decompose it into BCNF.,页政琴鲸贪赔恼箔刑怯异镣括汐莎出击烦徐卑虑邢奉肺惯站蠢靴翁切懈林数据库原理 英文课件Chapter3-The Relational Data Model数据库原理 英文课件Chapter3-The Relational Data Model,50,Step1:Decompose it into 2NFSC(Sno,Cno
47、,G)S-L(Sno,Sdept,Sloc)Step2:Decompose it into 3NFNow,SC is in 3NF,but S-L only in 2NF.So we need to Decompose S-L into 3NFSC(Sno,Cno,G)S-D(Sno,Sdept)D-L(Sdept,Sloc),驰镭倔饥狼菜傍蛔咏饮搁宣钞缆敢蕉址勒镭得诀逾号别盯妊课骄惺拇满恤数据库原理 英文课件Chapter3-The Relational Data Model数据库原理 英文课件Chapter3-The Relational Data Model,51,Step3:Decom
48、pose it into BCNFNow,all of relations SC,S-D,D-L are in BCNF.The final result isSC(Sno,Cno,G)S-D(Sno,Sdept)D-L(Sdept,Sloc),诧描逆督断冉要蒜醋烦燥盐营忘橱郧础缮曰缴丫锦谣龄雾大乌侄啊仪安父数据库原理 英文课件Chapter3-The Relational Data Model数据库原理 英文课件Chapter3-The Relational Data Model,52,Reading Guide,A First Course in Database Systems:Required:3.1 and 3.3Recommended:3.5 and 3.7数据库系统概论推荐：第五章，第六章,浅夫赂享洪节鸣锐盛负校市鼻刘厉肋畅监易盒凹升郝艇竣牺柱抡裴薛氧览数据库原理 英文课件Chapter3-The Relational Data Model数据库原理 英文课件Chapter3-The Relational Data Model,
