EER Model Handout

8/6/2019 EER Model Handout

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Enhanced-ER Data Model

CS4710 Introduction to Database Systems

Instructor: Yi-Shin ChenOffice: EECS 3201Email: [email protected]

Office Hour: Tu. 1-2PM, Th. 3-4pm

2007/3/13 Introduction to Database Systems 2

Motivation

ER data model is useful to describe traditionalapplicationsNewer types of applications were difficult to model, forexample:

Design and manufacturing (CAD/CAM)

Geographic Information Systems (GIS)These applications had more complex requirementsSemantic data modeling concepts needed to beincorporated

Result Enhanced (or Extended) ER data model


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EER Model ConceptsIncludes all modeling concepts of basic ERAdditional concepts: subclasses/superclasses,specialization/generalization, categories,attribute inheritanceIt is used to model applications more completelyand accurately if neededIt includes some object-oriented concepts, suchas inheritance


Key Ideas of EERGeneralization

Compute the union of two or more entity sets (or subclasses) Produce a higher-level entity set (or superclass) Containment relationship between the superclass and subclass(es)

Specialization

Construct the subclasses that are a subset of superclassesReverse of generalization

Example

We focus on specialization afterward


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Why SpecializationThe process allows us to

Define a set of subclasses of an entity typeEstablish additional specific attributes with eachsubclassEstablish additional specific relationship sets betweeneach subclass and other entity sets


Subclass

Subclass entities inherit attributes from the superclassAn entity can be a member of a number of subclasses

An entity cannot just being a member of a subclass but not superclassIt is not essential that every entity in a superclass be a member of somesubclass

Person

Employee Alumnus Student

Sex Name ID Address DoB

Salary MajorClass


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Different Types of SpecializationPredicate-defined (or condition-defined)

Determine subclass membership by examining the value of aspecific attribute (termed defining attribute)

User-definedThe user specifies subclass membership individually

Secretary Faculty Technician

Sex Name ID Address DoB

Typing Speed SpecialtyResearch Interest

Employee


Different Types of SpecializationDisjoint: an entity can be a member of at most one subclassOverlap: when the subclasses are not disjoint

Total: each entity must be a member of some subclassPartial: An entity might belong to no subclass

Disjointness and completeness constraints are independentHence, four combinations are possible


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Categories (UNION TYPES)In some cases, need to model a singlesuperclass/subclass relationship with more than onesuperclass

Superclasses represent different entity typesSuch a subclass is called a category or UNION TYPE

Example: Database for vehicle registration, vehicleowner can be a person, a bank (holding a lien on avehicle) or a company.

Category (subclass) OWNER is a subset of the union of thethree superclasses COMPANY, BANK, and PERSON


Example of Categories


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Category Member vs. Shared Subclass

A category member must exist in at least one ofits superclassesNote: The difference from shared subclass,which is subset of the intersection of itssuperclasses (shared subclass member mustexist in all of its superclasses).


Example: Railway System

Each line has a unique line codeLines may run via mountain or seaEach line is associated with origin, destination, intermediate stops, andall scheduled departure time, and scheduled arrival timeNot every line runs every dayEvery time the line runs must be recorded.

There are four types of trains: each has fixed carsTzeChiang, ChuKuang,TzeChiang: the fastest oneChuKuang: the second fastestFuHsing: the slowest oneEMU: where customers can sit anywhere

TicketsThe types of tickets are classified into normal, half-fare, and platformtickets


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Example: Railway System (Contd.)Information of normal and half-fare tickets includes

The originThe destinationPriceThe line he takesThe date he takesCar number and seat number should also be recorded except for EMUIf all seats were sold out, passengers will get tickets without seatsIf a customer bought a round trip ticket, he could get 10% discount

Customers can book tickets by the Internet or by telephoneOne customer can book up to four tickets at one time

Booking information includesPersonal ID of the customerThe date he booked the ticketsThe information of the ticketsBooked tickets are only reserved for 5 days

If a customer didnt pay for the booked tickets in time, the booking is invalidand the seats are released for other customers


Example: Reservation System

Reservation System for airline companiesEach company has many aircrafts

Each has a registration number, make, model, and the maximumcapacity of passengers

Each company has many flightsFlights can be classified into domestic or international routesEach flight departs from and arrives at registered airports

An airport also has an airport code, description name, city and countryFlight may stop at some intermediate stopsCustomers could take a transfer flight from intermediate stops

Each flight has three seat classesFirst Class, Business Class, and Economy class

For every flight, the system should store a list of available seatsThe seat arrangements are associated with aircraftsEach seat can only be reserved to one customerTicket prices are associated with classes and time

Customers can make reservation without reserving seatsEach flight allow 20% overbooking


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Example: Reservation System (Contd.)

The reservation system should keepA unique identifier for each customer

This identifier is assigned automatically once customers make anew reservation in the system

Customer informationFlight informationThe time that reservation was madeA credit-card number associated with the reservationA flag which indicates whether this particular reservation is paid

or notWhen a reservation is paid it is transformed automatically to a ticketThe reservation can be canceled before flight departure, howeverthe ticket is still valid (to exchange some products)

Each reservation might be associated with many flights


Example: Registration-SystemFor University System of Taiwan (UST)Each school has many departmentsEach department will offer many courses

Some courses are specially designed for students majoring insome subjects

Some courses will be offered regularlyFor some courses, there will be many classes in one semestertaught by different instructorsSome courses will have prerequisite subjectsSome classes will control the number of seatsThe system should avoid time conflicts when students scheduletheir courses


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Example: Registration-System(Cond.)

Some courses are specially designed for graduate studentsGraduate students can become TAs of certain classes

However, he/she has to take this course beforeA full-time student should enroll in at least

8-units/semester for graduate students6-units/semester for graduate students who have TA/RAships12-units/semester for undergraduate students

The instructors of classes can beFaculty

PhD students (who can only teach undergraduate-level classes)Students receiving RAships should work with some faculty


Example: Movie On Demand System

The movie-on-demand (MoD) provider operates severalvideo servers in different geographical locations that letcustomers view movies at home via a special set-top boxthat interfaces with their TV and that further connects tothe video server network.The database must represent the following information:

Video Movie InformationA movie has a title, release date, rating, running time, director, andone or more actorsMovies are split between domestic and foreign movies

A foreign movie uses a language other than English and may provideEnglish subtitlesDomestic movies are further categorized into comedy, drama, action,and horror movies

A comedy movie has the degree of funniness which rangesbetween 1 and 5A drama movie has a short description such as love story,documentary, humanity, etc.


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Example: Movie On Demand System (Con.)

Each movie could be reviewed by one or more critics, each of whomevaluates it as between zero and five stars

A critic has a name and a phone numberHe or she might review one or more movies

A movie may have won one or more academy awards (i.e., Oscars)If that is the case, then the movie has a list of all the categories in which it wonE.g., best picture, best actor, best actress, etc.

Each movie is stored on a number of different video serversEach video server has a unique ID and an address (location)If a customer requests a movie then that movie is delivered (streamed) from oneof the video servers to the customers homeEach movie can be supplied by only one distributor

One distributor might provide several moviesFor each distributor, the MoD provider keeps track of information about its name,address, and phone numberA distributors address can be accessed as street address, city, state, and zipcode individuallyHowever, the entire address of a distributor can also be retrieved as a unit



Employee InformationAn employee has a name, a social security number, date of birth, salary,and a phone numberHe or she may have a supervisorEmployees are either permanent or temporary, but not bothEach permanent employee has an employee numberAll supervisors are permanent employeesAn employee works at the location of one of the video servers

Customer InformationA customer has a social security number, a name, a phone number, andan addressEach customer must have one or more credit cards

Each credit card includes a type of credit card (Visa/MasterCard/), a cardnumber, and an expiration date.

Viewing Transaction InformationEach customer can view movies from a video serverFor each viewing transaction, the viewing date and time is recorded.


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Bill Statement InformationEach customer receives one bill statement after each viewingtransactionEach statement has a billing date, a billing number, one or moremovie titles, and a total charge.A billing number is unique for a particular customer

It is not unique across different customersRelease Charge Information

For each movie, a release type is definedArbitrarily recent movies are marked as new release, whereasothers are marked as ordinary release.

The store keeps track of different charge information for differentrelease typesFor newly released movies, the fee is $100 for the first viewing and$30 for each additional viewingFor the other ones, the fee is $50 for the first viewing and $15 foreach additional viewing

Documents

EER Model Handout