Jarrar: Subtype Relations and Constraints

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Subtype Relations & Other Constraints
Knowledge Engineering (SCOM7348)
Lecture Notes on Subtype Relations & Other Constraints
Birzeit University
2011
Dr. Mustafa Jarrar
University of Birzeit
mjarrar@birzeit.edu
www.jarrar.info
(Chapter 6)

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Conceptual Schema Design Steps
1. From examples to elementary facts
2. Draw fact types and apply population check
3. Combine entity types
4. Add uniqueness constraints
5. Add mandatory constraints
6. Add subtype relations and other constraints
7. Final checks, & schema engineering issues

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Outline
• Quick Math background
• Value Constraints
• Set Constrains
o Subset
o Equality
o Exclusion
• Subtype relations
• Frequency constraints
Information adapted from [1]

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Mathematical Background
Hypothetical Euler diagrams for set comparisons.

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Venn diagrams for three set-forming operations.

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Venn diagrams for (a) A is a proper subset of B and (b) four sets.

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Outline
• Set Constrains
o Subset
o Equality
o Exclusion

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Value Constraint
Called Value Constraint
A set of values, from
which the value of
the MedalKind is
limited to

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Value Constraint
The value of sex should be one of {‘M’, ‘F’}

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Value Constraint
Value constraints may list the possible values of a value type.
 Who can give more examples?

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Outline
• Set Constrains
o Subset
o Equality
o Exclusion

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Role subset/equality constraint
Subset constraint:
Every Member booked an Hour
should play sport.
Equality constraint:
Every Member ‘has’ ReactionTime
should ‘has’ HeartRate, and every
Member ‘has’ HeartRate should
‘has’ ReactionTime.

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Role subset constraint
Notice that this subset constraint is
implied, and should be removed.
That is, there is no need to say that every A
playing r2 must also play r1 (subset), because the
mandatory constraint here means that every A
must play r1 (the Mandatory implies the subset).

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Role equality constraint
Also this quality constraint is implied,
and should be removed.

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Implication
Who can explain the difference?
The two constraints in the first model says: each A must play r1 or r2 (or
both), and that if A plays r2 then it must play r1. This means that r1 must
be always played (which is the second model)

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Role Exclusion Constraint
Exclusion constraint:
Every Employee is allocated a
ParkingSpace should not claim
MoneyAmt.

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Each partner must be either a husband
or wife (but not both at the same time).
Called “Exclusive-or”

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Exclusive-or (another example)
Each Account must be
OwnedBy a Person or a
Company, but not both.

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Each person has at most one of three vices. i.e., from 0 to 3 vices.
It can be written also as

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Pair Exclusion Constraint
How can we restrict that a
person can drive a car only if
he owns that car.

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Pair-subset constraint
An example of a tuple-subset constraint between sequences of three roles.

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Equality Constraint

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Pair Exclusion Constraint
Same person can ‘own’ and ‘wants to buy’ the same car?

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What is Wrong?
 
Implies
 
ImpliesImplies


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Outline
• Set Constrains
o Subset
o Equality
o Exclusion

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Subtypes
Person
Male Female
• Generalization/Specialization hierarchy.
• Subtype inherits the properties of its supertype.

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Subtypes
Person
Australian Female
Female
Australian
*
* The indirect subtype connection is implied, so it should be omitted

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Subtypes
Person
Male Female
There is no person that
can be Male and Female
at the same time.
Person
Male Female
Every person must be a
Male or a female.
Every person must be
either a Male or a Female
Person
Male Female

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Outline
• Set Constrains
o Subset
o Equality
o Exclusion
• Frequency constraints also called “Occurrence constraints”

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Frequency constraints
To indicate that each entry in a fact column must occur there exactly n
times, the number n is written beside the role.
Each city in the first
column must occur
three times.
each drive kind in the
Second column must
appear there twice
A compound transaction is needed to initially populate this fact type
requiring at least six facts to be added.

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Frequency constraints
Each member of pop(r) occurs there exactly n times.
n must be a positive integer.
A r
n
A r
1
A r
If n = 1, this is equivalent to a uniqueness constraint

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Ranged Frequency Constraint
Examples of minimum and maximum frequency constraints.
Each name of Panl must occur at least 4
and at most 7 times. That is, each Expert
must on 4 to 7 Panels
Each Expert can referee 5 papers
Each Paper can be refereed by at least two Experts.

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Discussion
Summarize what you learned? And what you think about it?
Compare what you learned with EER and UML?
Questions & Suggestions?

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References
1. Terry Halpin, Tony Morgan: Information Modeling and Relational
Databases, Second Edition. Second Edition. The Morgan Kaufmann Series in
Data Management Systems. ISBN: 0123735688

Jarrar: Subtype Relations and Constraints

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