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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)
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Semantic Modeling 3CIS
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 )
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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
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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.
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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
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E-R Notation
Entity Relationship
Attribute Primary Key
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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
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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
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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#
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Semantic Modeling 12CIS
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
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Semantic Modeling 13CIS
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
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Semantic Modeling 14CIS
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
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Semantic Modeling 15CIS
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
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Semantic Modeling 16CIS
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
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Semantic Modeling 17CIS
Relationship Attribute
oDescribes the association
4A adverb or noun in requirement specification
Instructor Courseteaches
sect# time
dateroom#
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Semantic Modeling 18CIS
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
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Semantic Modeling 20CIS
Recursive Relationship called
Superviseswith Role Names
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Semantic Modeling 21CIS
Entities associated through two distinctRelationships with Role Names
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Semantic Modeling 22CIS
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
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Semantic Modeling 23CIS
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
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Semantic Modeling 24CIS
Multiplicity
Teaches TakesFaculty Course Student
(1,45)(0,4) (1,1) (?,?)
O h E R M d l
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Semantic Modeling 25CIS
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
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Semantic Modeling 26CIS
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
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Semantic Modeling 27CIS
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
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Semantic Modeling 28CIS
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
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Semantic Modeling 29CIS
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
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Semantic Modeling 30CIS
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.
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