David M. Kroenke’s,
th
10
ed.
Database Processing:
Fundamentals, Design, and Implementation
Chapter Five:
Data Modeling with the
Entity-Relationship Model
Part One B
DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition
© 2006 Pearson Prentice Hall, modified by Dr. Lyn Mathis
5-1
Data Modeling Notation
(a) and (b)
NOT
Equivalent
Statements
DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition
© 2006 Pearson Prentice Hall, modified by Dr. Lyn Mathis
5-2
Data Modeling Notation:
ERwin
DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition
© 2006 Pearson Prentice Hall, modified by Dr. Lyn Mathis
5-3
Data Modeling Notation:
N:M and O-M
Note that:
ERwin cannot
indicate true
minimum
cardinalities on
N:M relationships
Hand-draw the
minimum
cardinality symbol
DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition
© 2006 Pearson Prentice Hall, modified by Dr. Lyn Mathis
5-4
ID-Dependent Entities
•
•
•
•
Always a child entity
Parent must exist first
Identifier includes the identifier of parent
The minimum cardinality
– from the ID-dependent entity
– to the parent is always one.
DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition
© 2006 Pearson Prentice Hall, modified by Dr. Lyn Mathis
5-5
ID-Dependent Entities: Logical
Dependence on Parent
A solid line
indicates an
identifying
relationship
DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition
© 2006 Pearson Prentice Hall, modified by Dr. Lyn Mathis
5-6
ID-Dependent Entities:
Important Features in Template
•
•
•
•
•
•
•
Solid relationship line
1:M relationship
Hash mark by parent, always
Child often optional, but not always
Identifier of parent part of identifier of child
Parent symbol has sharp corners
Child symbol has rounded corners
DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition
© 2006 Pearson Prentice Hall, modified by Dr. Lyn Mathis
5-7
Weak Entities
• Existence depends upon another entity
• All ID-Dependent entities
• Other non-ID-dependent weak entities
(identifier of the parent not part of the
identifier of the weak child entity)
DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition
© 2006 Pearson Prentice Hall, modified by Dr. Lyn Mathis
5-8
Non-Identifying Weak Entities
A dashed line
indicates a
nonidentifying
relationship
DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition
© 2006 Pearson Prentice Hall, modified by Dr. Lyn Mathis
Weak entities must be
indicated by an
accompanying text box in
Erwin – There is no
specific notation for a
nonidentifying but weak
entity relationship
5-9
Non-Identifying Weak Entities
•
•
•
•
•
Dashed line between parent & child
Hash mark by parent
Parent always required
Child often optional, but not always
In Erwin, rounded corners not possible
– For weak entity (child)
– Technically, should be rounded
DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition
© 2006 Pearson Prentice Hall, modified by Dr. Lyn Mathis
5-10
Subtype Entities
• A special case of a supertype entity
• Supertype contains all common attributes
• Subtypes contain specific attributes.
• Discriminator attribute possible
– In supertype
– Indicates the subtype.
DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition
© 2006 Pearson Prentice Hall, modified by Dr. Lyn Mathis
5-11
Mutually Exclusive
Subtype Example
ssn
FACULTY
Division
Rank
EMPLOYEE
name
1
HOURLY
program
title
Salary vacation
address
SALARIED
title
wage
DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition
© 2006 Pearson Prentice Hall, modified by Dr. Lyn Mathis
salary
5-12
Inclusive
Subtype Example
ID
PERSON
name
m
address
CUSTOMER
EMPLOYEE
pay rate
credit limit
title
DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition
© 2006 Pearson Prentice Hall, modified by Dr. Lyn Mathis
charge card no
5-13
Subtypes – represent entities
with optional sets of attributes
• Inheritance
• Not always mutually exclusive
DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition
© 2006 Pearson Prentice Hall, modified by Dr. Lyn Mathis
5-14
Subtypes with a Discriminator
DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition
© 2006 Pearson Prentice Hall, modified by Dr. Lyn Mathis
5-15
Subtypes: Exclusive or Inclusive
• Exclusive, one supertype relates to at
most one subtype.
• Inclusive, one supertype can relate to one
or more subtypes.
DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition
© 2006 Pearson Prentice Hall, modified by Dr. Lyn Mathis
5-16
Subtypes: Exclusive or Inclusive
(Continued)
DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition
© 2006 Pearson Prentice Hall, modified by Dr. Lyn Mathis
5-17
Subtypes: IS-A relationships
• Called IS-A relationships
• Subtype IS A supertype
• Identifer of the supertype and all of its
subtypes must be identical
• Subtypes avoid value-inappropriate
nulls.
DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition
© 2006 Pearson Prentice Hall, modified by Dr. Lyn Mathis
5-18
ERwin Symbol Summary
DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition
© 2006 Pearson Prentice Hall, modified by Dr. Lyn Mathis
5-19
ERwin Symbol Summary (Continued)
DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition
© 2006 Pearson Prentice Hall, modified by Dr. Lyn Mathis
5-20
David M. Kroenke’s
Database Processing
Fundamentals, Design, and Implementation
(10th Edition)
End of Presentation:
Chapter Five Part One B
DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition
© 2006 Pearson Prentice Hall, modified by Dr. Lyn Mathis
5-21