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