Semantic Data Modeling

7/31/2019 Semantic Data Modeling

1/30

Semantic Modeling 1CIS

Semantic Data Modeling

oWhat is Conceptual Data Modeling

oEntity-Relationship (E-R ) Modeling

oLimitations of E-R Modeling

oObject-oriented Modeling: Another semantic

model (discussed later in this course)


2/30


3/30


Bridge the Gap

STUDENT( ID, Name, Age, Address, GPA )

INSTRUCTOR ( Emp#, Name, Rank, Dept )

COURSE ( Course#, Credits, Title )

CLASS ( Emp#, ID, Course#, Time, Room )

STUDENT( ID, Name, Age, Address, GPA )

INSTRUCTOR ( Emp#, Name, Rank, Dept )

COURSE ( Course#, Credits, Title )

CLASS ( Emp#, ID, Course#, Time, Room )


4/30Semantic Modeling 4CIS

Data Semantics

oStatic Information

u Data -- Entities

u Associations -- Relationships among entities

oDynamic Information

u Activities -- Operations/transactions

u Integrity constraints -- Business rules/regulations and data meanings



Conceptual Data Model Revisited

A conceptual data model consists of:o A collection of formal concepts

o A set of usage rules

Different model has different modeling capability

Conventional (Logicaldata modeling)

Conventional (Logical

data modeling)

Semantic datamodeling

Semantic datamodeling

Object-Oriented

data modeling

Object-Orienteddata modeling

-- Hierarchical

-- Network-- Relational

-- E-R

-- EER-- etc.



E-R Modeling

o Introduced by Peter Chen in 1976

oBasic modeling concepts:

u Entities, entity types, and attributes

u Relationships

Instructor OfficeAssigned1 1

DepartmentWorks_for

N

1

Teaches

N

M

Course

Date

Language

Emp#

Name

FName

MInit LName

Time

Location

Date



E-R Notation

Entity Relationship

Attribute Primary Key


8/30Semantic Modeling 8

CIS

Entities

oAn entity is a conceptual objectoPhysically exists

4Usually a noun in requirement specification

CIS 2010CIS 3730

Jose Alice Steve

Acct CIS

Class

Student

Department



CIS

Entity Types

oA collection of similar entities

oAn abstraction of "physical" entities

4A noun in requirement specifications

4Having "independent" meaning

DepartmentDepartment

StudentStudent

CourseCourse

AcctCISJose

Alice

Steve

CIS 3730CIS 2010



CIS

Weak Entity Types

oCan't exist in DB independently

oMust be identified by its owner

u Owner entity type

u Identify relationship

u Partial key

u Total participation

Student Registers Car

Date

1N

Color PNumParkingLot#


11/30


12/30


Key Attributes

One or a group of attributes that can uniquely identifyindividual entities of an entity type

u A key refers to one or a group of attributes as a whole

u A key attribute is a component attribute of a key

u Key changes with data semantics

An entity type may have several qualified keys

u Primary key -- One of the candidate keys

u Alternate key - Candidate keys not used as the primary key

u Secondary key -- An identifier of records with similar properties of interest

4The primary key attribute(s) is(are) underlined


13/30


More Attributes

StudentStudent

id

age

name

degrees

FnameMname

Lname

oSimple attributeContains atomic values only

oComposite attribute

Has component attributes

__________________________________

oSingle-valued attribute

Has exactly one value per entity

oMulti-valued attribute

Contains repeating values per entity

__________________________________

oDerived attribute

Attribute values computed by means of

other attributes

SalesrepSalesrep

Fname

Mname

Lname

EmpNo

CommRate

CommEarned


14/30


Relationships

Associations among entitiesu Relationships -- Associations among entities

4Usually a verb in requirement specification

Occurrence Diagram or Semantic Net

CourseStudent

Takes

Joseph

Alice

Sue

Tom

Peter. . .

CIS2010

CIS3210

CIS3215

CIS3730

CIS8140

. . .

Student CourseTakes


15/30


Relationship Degrees

The number of entity types associated with that relationship.Each entity in a relationship is known as aparticipant.

Unary

Supervises

EmployeeEmployeeEmployeeEmployee DepartmentDepartmentWork

Binary

n-aryTernary

ProjectProject

Part

PartSupply

SupplierSupplier


16/30


N-ary Relationships

oA link must associate with all participants

oCardinality is with respect to individual relationships

4A N-ary relationship is not equivalent to N binary

relationships

Salesperson Order

Customer

ships

N

M 1


17/30


Relationship Attribute

oDescribes the association

4A adverb or noun in requirement specification

Instructor Courseteaches

sect# time

dateroom#


18/30


Relationship Cardinality

How entities are connectedthrough a relationship

u One-to-One -- An entity ofE1 is

connected to at most one entity ofE2

and vice versa.

u One-to-Many -- An entity ofE1 may

be connected to one or more entities

ofE2, but an entity ofE2 can only be

mapped to at most one entity ofE1.u Many-to-Many -- An entity ofE1

may be linked to one or more entities

ofE2, and vice versa.

[ ][ ]

[ ]...

abc

...

xyz

...

E1 E2R

1 1

[ ]

[ ][ ]...

a

bc...

x

yz

...

1 M

...

abc...

xyz

...

M N


19/30


20/30


Recursive Relationship called

Superviseswith Role Names


21/30


Entities associated through two distinctRelationships with Role Names


22/30


Participation ConstraintsLetR be a relationship type involves entity type E as a

participant. If every instance ofE participates in at least one

instance ofR, then the participation is said to betotal; other

wise it is said to be partial [Date, 2004]

oPartial (optional)

participation

An entity ofE does not have to be

mapped to another entity through therelationship.

oTotal (mandatory)

participation

Every entity ofE must be connected

through the relationship to other entity

( or entities ).

WriterWriter

Publishes

BookBook

M

1

St t l C t i t


23/30


Structural Constraints

Main type of constraint on relationships is calledmultiplicity.

Multiplicity - number (or range) of possibleoccurrences of an entity type that may relate to asingle occurrence of an associated entity typethrough a particular relationship.

Represents policies (called business rules)established by user or company.

M lti li it


24/30


Multiplicity

Teaches TakesFaculty Course Student

(1,45)(0,4) (1,1) (?,?)

O h E R M d l


25/30


Other E-R Models

Entity 1 Entity 2Relationship

RelationshipEntity 1 Entity 2

attr. 1attr. 2

RelationshipEntity 1 Entity 2( 1:m ) ( 0:5 )

P d C f E R


26/30


Pros and Cons of E-R

Emp#, Name, Address

Salary, Skill

Advantagesu Simple and easy to understand.

u Very popular.

u Semantic richer than classical datamodels.

Disadvantages:

uNot a formally defined data model.

u Deals with some integrity constraints.

u Difficult to distinguish entities from

relationships.

u Has redundant modeling information.

Project

Manager

Project

Dependent

Project

MemberWorks-on

m-has

Manageshas

Emp#, Name, Address

Salary, Skill

ID, NameAddress

Birth-date

I A R l ti hi


27/30


Is-A RelationshipoGeneralization and specialization hierarchy

u Supertypes -- Hide the differences of subtypes

u Subtypes -- Reveal specific properties

Person

Student Staff

UnderGrad Grad Faculty Secretary

Generalization

SpecializationIs-A Is-A Is-A Is-A

Is-A Is-A

I h it


28/30


Inheritance

oA supertype contains the common properties of all its subtypeentities.

oSubtype inherits properties of its supertype and may have its

own properties.

PersonPerson

EmployeeEmployee DependentDependent

Project

Member

Project

Member

Project

Manager

Project

Manager

ID, Name, Address

Birth-dateSalary, Skill

Is-A Is-A

Is-A Is-A

Ratio-of-success, ... Languages, ...

ER E l I l i


29/30


ER Example In-class exercise

A database is being constructed to keep track of the teams and games of abaseball league. A team has a number of players, not all of whom participate in

each game. It is desired to keep track of the players participating in each gamefor each team, the positions they played in that game, and the result of thegame. Design an ER schema diagram for this application

Assumptions:Each game in the schedule is identified by a unique Game#, and a game is alsoidentified uniquely by the combination of Date, starting Time, and Field where itis played. A performance attribute is used to store information on the individual

batting performance of each player in a game.

EER Modeling Example


30/30


EER Modeling Example

American Airlines CompanyThe American Airlines Company publishes a monthly flight log report that tracks

which type of aircraft and the number of hours that were flown by anindividual pilot. A separate report is prepared for each pilot and is used to

monitor pilot flight proficiency for the two types of aircraft (fixed-wing androtorcraft) which a pilot may be qualified to fly.

The following business rules apply to this report. Pilots may be assigned to flydifferent aircraft each day by the flight scheduling manager. Each aircrafthas a single crew chief permanently assigned to perform maintenance on the

aircraft, although a crew chief may crew more than one aircraft. Eachaircraft is identified by an aircraft number. There are several aircraft types inthe fleet. An aircraft number is unique within an aircraft type.

Identify the entities in this situation and draw an E-R diagram of the entities toinclude their relationships and any attributes identified in this example. Give

examples of additional attributes that might be associated with each entity.

Documents

Semantic Data Modeling