CSCI 5333 Data Base Management
System
Spring 2002 (1/14-5/6)
Week 2:
Semantic Data Modeling (Ch. 4)
A. Enhanced ER Modeling
concepts
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definition
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example
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subclass
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superclass
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class/subclass relationships
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type inheritance
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specialization
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generalization
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category
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union
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attribute and relationship
inheritance
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EER Diagrams
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- Question: Why specialization? HINT:
pp.76-77.
- Class/Subclass properties:
- predicate-defined subclasses,
defining predicates
- disjointness constraint: disjoint, overlapping
- completeness constraint: partial subclasses,
total subclasses
- Multiple Inheritance: specialization/generalization lattice
(see Fig. 4.6)
- Formal Definition: (page 93) A category T is
a class that is a subset of the union of n defining superclasses D1, D2,
..., Dn, n > 1.
- NOTE: The formal definition applies to the whole category
. That is, some instances of the categories may be D1, some D2, etc.
- At the instance level, each instance of the category
is of one and only one of the superclasses. That is, an instance of T is
either D1, D2, D3, ..., or Dn (no overlapping).
- Question: Describe the difference between 'multiple
inheritance' and 'category'.
Ø
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Index
B. Object Modeling using UML Class Diagrams
- Question: Both EER and UML are examples
of semantic data modeling. Is there anything that can be represented
in UML but not in EER? HINT: p.74.
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Comparison between EER and UML:
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EER
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UML
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Examples from p.94
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Examples from p.96
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Entity type
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Class
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EMPLOYEE
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Entity
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Object
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an instance of EMPLOYEE
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Relationship
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Association (type 1 relationship)
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WORKS_FOR
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Relationship attributes
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Link attributes
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the MANAGES box
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Relationship constraints
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Multiplicities
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4..*, 0..1, 1..*, *, 0..*
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Recursive relationships
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Reflexive associations
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supervisee / supervisor
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multi-valued attributes
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Aggregations (type 2 relationship), also
called part-of relationship
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LOCATION is part of DEPARTMENT
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Weak entity
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Qualified association/aggregation
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DEPENDENT
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Inheritance
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represented as a blank triangle between
a subclass and its super class(es)
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STAFF is a subclass of EMPLOYEE. STUDENT_ASSISTANT
is a subclass of STUDENT and EMPLOYEE (multiple inheritance).
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Overlapping specialization
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represented as filled triangle between
the superclass and its subclasses
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A PERSON may be an EMPLOYEE, an ALUMNUS,
a STUDENT, or combination of those.
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Disjoint specialization
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represented as a blank triangle between
the superclass and its subclasses (the default inheritance relationship)
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An EMPLOYEE is a STAFF, a FACULTY, or a
STUDENT_ASSISTANT, but not more than one of them.
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Total completeness
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? (seems to be missing in UML) |
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C. Modeling of Aggregation (part-of relationship) in EER
Case A
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as multivalued attributes
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See Fig. 3.15 (p.65): Locations
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Case B
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as weak entities
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See Fig. 3.15 (p.65): Dependent_of
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Case C
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as weak entities in a ternary relationship
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See Fig. 4.16 (p.104): Interview
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Question: How is aggregation modeled
using UML? Ans.: See p.94.
Review Questions (p.105)
4.1.
What is a subclass? When is a subclass needed in data modeling?
4.3.
Discuss the mechanism of attribute/relationship inheritance. Why is it
useful?
4.4.
Discuss user-defined and predicate-defined subclasses, and identify the
differences between the two.
4.5.
Discuss user-defined and attribute-defined specializations, and identify
the differences between the two.
4.6.
Discuss the two main types of constraints on specializations and generalizations.
4.7.
What is the difference between a specialization hierarchy and a specialization
lattice?
4.8.
What is the difference between specialization and generalization? Why
do we not display this difference in schema diagrams?
4.9.
How does a category differ from a regular shared subclass? What is a
category used for? Illustrate your answer with examples.
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Index
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Main
page