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2009/03/04
DatabaseDatabase:
A collection of related data.
A databse is nothing more than a collection of information that exists over a long period of time
Data + Semantic = information
Data modelingA data model provides users with a conceptual representation of data that does not include many of the details of how the data is stored Data abstraction Object Definition LanguageE/R modelRelationsRelational databaseObject oriented database
Class Star { attribute string name; attribute Struct Addr { string street; string city; } relationship Set starredIn inverse Movie::stars } MoviesStarsInStarstitleyearlengthfilmtypetitletitleObject Definition LanguageE/R model
E/R (Entity-relationship)modelEntity (Object- a thing in the real world with an independent existenceRelationship relationships between entities
instancesattributesEntityRelation
Dimensionality of relation
Dimensionality of data cube
Relationship degreeEmployeeWorkforDepartmentDegree of 2DepartmentWorkforEmployee
Relationship degreeProjectSupplyPartSupplier
SupplierSupplyProjectDegree of 3Part
Constraint type of 1:1 relationshipDepartmentManagesEmployeeEmployeeManagesDepartment11
Constraint type of N:1 relationshipDepartment(1,1)EmployeeEmployeeWorkforDepartmentN1Workfor(2,N)
Constraint type of 1:N relationshipDependent(0,N)EmployeeEmployee1N(1,1)DependentOfDependentOfDependent
Constraint type of 1:N relationshipProject(0,N)DepartmentDepartment1N(1,1)ControlControlProject
Constraint type of N:M relationshipDepartmentWorkforEmployeeEmployeeWorkforDepartmentNM(1,N)(2,N)
Constraint type of N:M relationshipProjectWorkOnEmployeeEmployeeWorkforDepartmentNM(1,N)(2,N)
ProjectSupplyPartSupplierConstraint type of N:M relationship
SupplierSupplyProjectPart
E-R diagram for the company schemaEmployeeWorkforDepartment(1,1)(4,N)Manages(0,1)(1,1)ProjectControlWorks_onDependentsDependents ofnameFnameLnamesexssnRelationshipName(1,N)(1,N)(1,1)(0,N)(0,N)(1,1)StartDateNameLocationsSexBirthdayNumberHoursNumberNameLocations(1,N)
E-R diagram for the company schemaEmployeeWorkforDepartmentN1Manages11ProjectControlWorks_onDependentsDependents ofnameFnameLnamesexssnRelationshipNameMNN11NStartDateNameLocationsSexBirthdayNumberHoursNumberNameLocations
An example of a simple relational database
External viewExternal viewConceptual SchemaInternal SchemaExternal LevelConceptual LevelInternal LevelThree-schema architecture