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1、1Database Principles2Chapter 3The Relational Data ModeluRelational ModeluFunctional Dependencies3Contentsu3.1 Basics of the Relational Modelu3.3 From E/R diagrams to Relational Designsu3.5 Functional Dependenciesu3.7 Design of Relational Database SchemasuReading GuideuExercise4The things you should
2、knowuThe basic principle of relational database is proposed by E.F.Codd in 1970.uThe first RDBMS production is System RuThe most popular RDBMS DB2,Oracle,Ingres,Sybase,Informix,53.1 Basic of the Relational Model uThe relational model gives us a single way to represent data:as a two-dimensional table
3、 called a relation.6uAttributes(属性)w Attributes of a relation serve us as names for the columns of the relation.w Usually,the attributes describes the meaning of entries in the column below.7uSchemas（模式）w The name of a relation and the set of attributes for a relation is called the schema for that r
4、elation.w We show the schema for the relation with the relation name followed by a parenthesized list of its attributes.8uTuples（元组）w The rows of a relation,other than the header row containing the attributes,are called tuple.For example:w Relations,however,are sets of tuples,and it is impossible fo
5、r a tuple to appear more than once in a given relation.9uDomains（域）w 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.w Each attributes of a relation has particular elementary type,thus domain is decided.1
6、0uEquivalent Representations of a Relationw The attributes of the relation can be reordered without change the relation.11uRelation Instance（关系实例）w A relation about movies is not static;rather,relations change over time.w It is not common for the schema of a relation to change.w We shall call a set
7、of tuples for a given relation an instance of that relation.12An Example of Relation InstanceRelation:Person(Name,Address,Telephone)Relation Instance:NameAddressTelephoneBob123 Main St555-1234Bob128 Main St555-1235Pat123 Main St555-1235Harry456 Main St555-2221Sally456 Main St555-2221Sally456 Main St
8、555-2223Pat12 State St555-123513More uRelation(Instance)=a set of tuplesuDatabase=collection of relationsuRelation schema=relation name+attributesw Example:Movies(title,year,length,fileType)uDatabase schema=a set of all relation schemasw Movies(Title,Year,Length,FileType)w Star(Name,Age)w Studio(Stu
9、dioName,Addr)14Name Addr Tel N1 A1 T1 N2 A2 T2 N3 A3 T3 N4 T4 N5 T5 T6 T7Name Addr Tel N1 A1 T1 N1 A1 T2 N1 A1 T3 .N1 A1 T7 N1 A2 T1 N1 A3 T1 N2 A1 T1TupleDomainComponentAttribute15Integrity Constrain of RelationsuEntity Constrainw The attributes belong to key can not be set as NULL.uReference Const
10、rainw Foreign Key:an non-key attribute A in R is a key in S,then the A is called a foreign key of R.w The value of foreign key can only be NULL or same as what is in S.uUser-define Constrainw Users define the constrains themselves.16补充：关系的完整性u实体完整性u参照完整性u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
11、库系统自动支持17实体完整性u规则：若属性A是基本关系R的主属性，则属性A不能取空值u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u依据：现实世界的实体是唯一可分的例：学生（例：学生（学号学号，姓名，性别，专业号，年龄），姓名，性别，专业号，年龄）课程（课程（课程号课程号，课程名，学分），课程名，学分）选修（选修（学号学号，课程号课程号，成绩），成绩）18例：学生实体与专业实体间的关系：例：学生实体与专业实体间的关系：学生（学生（学号学号，姓名，性别，专业号，年龄），姓名，性别，专业号，年龄）专业（专业（专业号专业号，专业名），专业名）关系参照图外码外码参照关系参照
12、关系被参照关系被参照关系例：学生，课程，学生与课程之间的多对多联系：例：学生，课程，学生与课程之间的多对多联系：学生（学生（学号学号，姓名，性别，专业号，年龄），姓名，性别，专业号，年龄）课程（课程（课程号课程号，课程名，学分），课程名，学分）选修（选修（学号学号，课程号课程号，成绩），成绩）关系参照图被参照关被参照关系系参照关系参照关系学生关系专业关系学生关系专业关系专业号专业号学生关系学生关系 选修关系课程关系选修关系课程关系学号学号课程号课程号参照完整性主码？外码？19参照完整性u定义：外码定义：外码w 设F是参照关系R的一个或一组属性，若F与被参照关系S的主码相对应，则称F是R的外码（
13、详细定义见教材P54）u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（例：学生（学号学号，姓名，性别，专业号，年龄，班长），姓名，性别，专业号，年龄，班长）参照关系参照关系被参照关系被参照关系外码外码20用户定义完整性u用户定义的、具体应用中的数据必须满足的约束条件w 成绩：0100之间w 身份证、身份证和生日对应关系 213.2 From E/R Diagrams to RelationuFrom Entity Sets to Relationw Simplest approach(not always best):
14、convert each E.S.to a relation.w Create a relation of the same name and with the same set of attributes.22Movies(title,year,length,filmType)Stars(name,address)Studios(name,address)Example23u From E/R Relationships to RelationwRelationships in the E/R model are also represented by relations.The relat
15、ion for a given relationship R has the following attributes;1.For each entity set involved in relationship R,we take its key attributes as part of the schema of the relation for R.2.If the relationship has attributes,then these are also attributes of relation R.24Example:Owns(title,year,studioname)S
16、tars-in(title,year,starName)25E-RE-R图向关系模型的转换原则图向关系模型的转换原则u一个实体转换为一个关系模式，实体的属性就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是关系的属性，实体的码就是关系的码u对实体间的联系对实体间的联系w 一个一个1:11:1联系可以转换为一个独立的关系模式，也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可以与任意对应的关系模式合并w 一个一个1:n1:n联系可以转换为一个独立的关系模式，也联系可以转换为一个独立的关系模式，也可以与可以与n n端对应的关系模式合并端对应的关系模式合并w 一个一个m:nm:n联系转换为一个关系模式联系转换为一个关系模式w 三个或三个以上实体间的一个多元联系可以转换为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一个关系模式w 具有相同码的关系模式可以合并具有相同码的关系模式可以合并补充：补充：26如公司部门管理系统的如公司部门管理系统的E-R图及其转换成的关系模式图及其转换成的关系模式部门部门项目项目职工职工电话电话包括包括承担承担
