database management cop4540, scs, fiu enhanced entity-relationship and object modeling chapter 4
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Database ManagementCOP4540, SCS, FIU
Enhanced Entity-Relationship and Object Modeling
Chapter 4
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Database ManagementCOP4540, SCS, FIU
Supertypes and Subtypes
• Subtype: A subgrouping of the entities in an entity type that has distinct attributes
• Supertype: An entity type whose subtypes share common attributes
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Database ManagementCOP4540, SCS, FIU
Employee supertype with three subtypes
EMPLOYEE
Name Address
Date_hiredSSN
HOURLYEMPLOYEE
SALAREDEMPLOYEE CONSULTANT
Hourly_rate Annual_salary Stock_option Contract_No. Billing_rate
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Database ManagementCOP4540, SCS, FIU
Attribute Inheritance
• Subtype entities inherit values of all attributes of the supertype
• An occurrence of a subtype is also an occurrence of the supertype
• All common attributes of subtypes appear in the supertype
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Database ManagementCOP4540, SCS, FIU
Use of Supertype/Subtype
• There are attributes that apply to some (but not all) of the instances of an entity.
• The instances of a subtype participate in a relationship unique to that subtype.
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Database ManagementCOP4540, SCS, FIU
Unique relationship for a subtype
PATIENT
IDAdmit_date
Is_cared_forRESPONSIBLE
PHYSICIAN
Physician_ID
OUTPATIENTRESIDENTPATIENT
Checkback_dateDate_discharged
BED
Bed_ID
Is_assigned1 1
1N
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Database ManagementCOP4540, SCS, FIU
Generalization and Specialization
• Generalization: The process of defining a more general entity from a set of more specialized entities.
• Specialization: The process of defining one or more subtypes of the supertype.
• Top-down conceptual refinement process.
• Bottom-up conceptual synthesis.
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Database ManagementCOP4540, SCS, FIU
Example of generalization(a) Three entity types: CAR, TRUCK, and MOTORCYCLE
CARPrice
VIN Name
Make Model
No_of_Passengers
EngineDisplacement
MOTORCYCLEPrice
VIN Name
Make Model
EngineDisplacement
Year
Year
TRUCKPrice
VIN Name
Make Model
Capacity
EngineDisplacement
Year
Cab_type
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Database ManagementCOP4540, SCS, FIU
VEHICLEPrice
VIN Name
Make Model
EngineDisplacement
Year
CARNo_of_Passengers
TRUCK Capacity
Cab_type
(b) Generalization to VEHICLE supertype
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Database ManagementCOP4540, SCS, FIU
Example of specialization
PART
Unit_price
Description
Part_No
Qty_on_hand Location
Routing_number
Supplier_ID
(a) Entity type PART
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Database ManagementCOP4540, SCS, FIU
(b) Specialization to MANUFACTURED PART and PURCHASED PART
PART
Description
Part_No Qty_on_hand
Location
MANUFACTUREDPART
Routing_number
PURCHASEDPART
SUPPLIER
Supplier_ID
Supplies
Unit_Price
M
N
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Database ManagementCOP4540, SCS, FIU
Constraints in Supertype/Subtype Relationships (1)
• Completeness Constraints: Whether an instance of a supertype must also be a member of at least one subtype.– Total Specialization Rule: the double line
convention– Partial Specialization Rule: default (single line)
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Database ManagementCOP4540, SCS, FIU
Example of Completeness constraints
PATIENT
IDAdmit_date
Is_cared_forRESPONSIBLE
PHYSICIAN
Physician_ID
OUTPATIENTRESIDENTPATIENT
Checkback_dateDate_discharged
BED
Bed_ID
Is_assigned1 1
1N
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Database ManagementCOP4540, SCS, FIU
• Disjointness Constraints: Whether an instance of a supertype may simultaneously be a member of two (or more) subtypes– Disjoint Rule: the symbol “d”– Overlap Rule: the symbol “o”
Constraints in Supertype/Subtype Relationships (2)
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Database ManagementCOP4540, SCS, FIU
Example of disjointness constraints(a) Disjoint rule
PATIENT
IDAdmit_date
Is_cared_forRESPONSIBLE
PHYSICIAN
Physician_ID
OUTPATIENTRESIDENTPATIENT
Checkback_dateDate_discharged
BED
Bed_ID
Is_assigned1 1
1N
d
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Database ManagementCOP4540, SCS, FIU
(b) Overlap rule
PART
Description
Part_No Qty_on_hand
Location
MANUFACTUREDPART
Routing_number
PURCHASEDPART
SUPPLIER
Supplier_ID
Supplies
Unit_Price
M
N
o
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Database ManagementCOP4540, SCS, FIU
Constraints in Supertype/Subtype Relationships
• Subtype Discriminators: An attribute of the supertype whose values determine the target subtypes(s).– Disjoint (one subtype for each instance)– Overlapping (multiple subtypes possible)
• Such subtype is said to be predicate-defined.
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Database ManagementCOP4540, SCS, FIU
Example of Subtype Discriminator (1)
EMPLOYEE
Name Address
Date_hiredSSN
HOURLYEMPLOYEE
SALAREDEMPLOYEE CONSULTANT
Hourly_rate Annual_salary Stock_option Contract_No. Billing_rate
Type
Type = ‘H” Type = ‘C’
Type =
‘S’
d
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Database ManagementCOP4540, SCS, FIU
Example of Subtype Discriminator (2)
PART
Description
Part_No Qty_on_hand
Location
MANUFACTUREDPART
Routing_number
PURCHASEDPART
SUPPLIER
Supplier_ID
Supplies
Unit_Price
M
N
o
Part_type
M?
P?
M?=‘Y’ P?=‘Y’
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Database ManagementCOP4540, SCS, FIU
Modeling of UNION Types Using Category
• A category has two or more supertypes.
• Attribute inheritance works more selectively in the case of categories.
• If a category is total (not partial), it may be represented alternatively as a specialization.
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Database ManagementCOP4540, SCS, FIU
Example of Category (1)
COMPANY PERSON
ACCOUNTHOLDER BANKHas_Acct
M N
U
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Database ManagementCOP4540, SCS, FIU
Example of Category (2)
BUILDING LOT
U
PROPERTY
PROPERTY
d
BUILDING LOT
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Database ManagementCOP4540, SCS, FIU
An EER Conceptual schema for a university database
Figure 4.10