Database Design
Sections 4 & 5
Subtype, Supertype, Mutually exclusive,
non-transferability, transferable, 1:1, 1:M,
M:M, Redundant, Intersection entity, Barred
relationship, CRUD analysis
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DJs on Demand – Partial ERD
2
Reserved Words
 A reserved work is one that has a
specific meaning and function in the
computer system, language, or
database.
 Examples:
 NULL
 DATE
 DISTINCT
3
Video Store – example next slide
 Identify business rules
 Construct ERD
 Class activity
4
Video Store example

Read the given business scenario and walk
through the steps below.

1. Examine the nouns. Are they things of
significance?

2. Name each entity.

3. Is there information of interest about the
entity that the business needs to hold?

4. Is each instance of the entity uniquely
identifiable? Which attribute or attributes
could serve as its UID?

5. Write a description of the entity.

6. Diagram each entity and a few of its
attributes. Remember, entity names are
always singular.

7. Identify the relationships and draw them
on the ERD.
5
Video ERD
•TAPE/DVD
a copy of
number
format
on
MOVIE
id
title
category
the feature of
rented by
the renter
of
CUSTOMER
membership
number
last name
first name
phone number
featured in
ACTOR
stage name
real name
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Use Source Documents
 Source document assist in identifying
entities, attributes, and relationships
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Subtype
A subtype:
 inherits all attributes of the supertype
 inherits all relationships of the supertype
 usually has its own attributes or
relationships
 is drawn within the supertype
 never exists alone
 may have subtypes of its own
 is also known as a "subentity“
8
Subtype & Supertype
 Supertype (entity) can be subdivided
into Subtypes
 Example:
JOB
manager
clerk
sales
support
9
Attributes
 Supertype can have attributes at
supertype level
 Attributes at supertype level are for
all subtypes
 Subtypes can have own attributes for
only that attribute
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Example
EXAM
takes
STUDENT
taken
by
#number
*description
*weight
*date
*grade for written component
MIDTERM
*grade for
BONUS
QUESTIONS
oral presentation
FINAL
included
in
*extra pts for opt. paper
QUIZ
include
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Global Fast Food Employees
 STAFF is an entity with supertypes
 What are the attributes of STAFF?





#id
*first name
*last name
*DOB
*salary
 What subtypes exist in STAFF?





ORDER TAKER
*overtime
COOK
*training
OTHER
 Are there any attributes in any of the subtypes?
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Example: an incorrect subtypes in
the illustration.
 AUTOMOBILE subtypes
are not mutually
exclusive
 AUTOMOBILE possible
solution
 BUILDING subtypes
have problem of not
being exhaustive,
should be minimum of
2 types
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Subtype Needs
 Exhaustive:
 Every instance of the supertype is also an
instance of one of the subtypes.
 Treating all parts or aspects without omissions.
 2 or more items
 Mutually exclusive:
 Every instance of the supertype is of one and
only one subtype.
 A relationship that presents choices which are
unable to be true at the same time.
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Correctly identify subtypes
 When considering supertypes and
subtypes, you can use three
questions to see if the subtype is
correctly identified:
1. Is this subtype a kind of supertype?
2. Have I covered all possible cases?
(exhaustive)
3. Does the example fit into one and only
one subtype? (mutually exclusive)
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Nested subtypes
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Documenting Business Rules
 Source documents assist in
identiying:




entities
attributes
relationships
Some business rules are “implemented
by programming”
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Business Rules
 Recognize if Business rule is implemented
by the data model or by programming
 Example:
 Only an employee with a title of manager can
manage other employees
 The event planner must contact the customer
before the DJ can be assigned
 Business rules can be changed as society
changes or business leaders feel change is
needed
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Business rule types
 Structural
 Must be entered at time of initial data entry
 Example: When ORDER entered a staff id must
be entered
 Does not require code written to enforce
 Procedural
 Work flow related
 Programmed validation is procedural constraint
 Generally need to write code
 Example: Commission can not be > 25% of
salary
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Structural Business Rule examples:
20
Procedural Business Rule example:
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Discussion
 Students must have studied algebra and
geometry in order to sign up for
trigonometry. Could you represent this in
the ERD?
 • How would you implement this with
programming?
 • If the student had taken the subjects, can
you think of an additional business rule that
a school may want in this scenario?
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Each entity has




Name
Optionality
Cardinality
Transferability
Example on next slide.
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Relationship Transferability
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Relationship transferability
 Rules established for the purpose such as
safety, efficiency, or increased profit
 Example: Airline tickets
 can be transferable or non-transferable?
 Non-transferable means also not updatable

symbol used to denote nontransferable
 blood type is non-transferable
25
Non-transferable relationship
place
CUSTOMER
ORDER
placed by
 Orders are non-transferable
 Resolution would be to cancel order
and create new order
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Example 5.1 exercise 1 a
 Each town may be the birthplace of
many people. Each person must be
born in one and only one town.
birthplace
for
PERSON
TOWN
born in
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Relationship types
 One to One (1:1)
 One to Many (1:M)
 Many to Many (M:M)
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One to One relationship
29
One to One relationship
 Usually few of these relationships
 Often mandatory at one side
 If mandatory at both ends be aware,
it might be a error. Possible should
be only one entity not two
ride
PERSON
ridden by
BYCYCLE
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One to One relationship
31
One to Many relationship
32
One to Many
 Most common type are mandatory on
one side and optional on the other
 Mandatory at both ends models
entities that cannot exist without
each other
ORDER TYPE
ORDER
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One to Many example
TAX RETURN
composed of
entered in
BAND
composed of
TAX REPORT
LINE
MUSICIAN
belong to
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Many to Many relationship
35
Many to Many
 Often common in initial version of
ERD
 Later stage of design converted to
other type
learn from
TEACHER
STUDENT
educate
36
Redundant relationship
 Redundant relationship is one that
can be derived from another
relationship in the model
37
Many to Many Relationship
Resolution
 All M:M relationships must be
changed to a set of 1:M and M:1
relationship
 Insert a transition entity between
 Occurs when you go from conceptual
model to design model
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Example: M:M with Intersection
Entity
COURSE
STUDENT
REGISTRATION
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Resolving M:M with Intersection
 Create an intersection entity
 If you can’t find a good intersection
entity create one by concatenate two
entities together
40
Example
EVENT
PARTNER
WORK ASSIGNMENT
(PARTNER_EVENT)
41
CRUD analysis
 Create ER models that reflect all
business rules gathered during the
interview process
 Identify the create, retrieve, update, and
delete (CRUD) requirements of the
business
 Validate your ER model by performing a
CRUD analysis
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CRUD requirements
 CRUD analysis will help you:
 Translate between the consultant and the client.
 Provide a guideline for the DBA who will
eventually build the database.
 Check that you haven’t missed any entities or
relationships in your data model.
 Check to make sure that you haven’t modeled
anything that the business does not require.
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What is CRUD?
 CRUD is an acronym for create,
retrieve, update, delete.
 Check for completeness and
accuracy.
44
Create keywords
Look for these words when you
interview the client.
 INPUT
 ENTER
 LOAD
 IMPORT
 RECORD
 CREATE
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Retrieve keywords








Look for:
VIEW
REPORT
BRING UP
PRINT
FIND
READ
LOOK UP
46
Update keywords





Look for:
CHANGE
MODIFY
ALTER
UPDATE
47
Delete keywords






Look for:
DISCARD
REMOVE
TRASH
PURGE
DELETE
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CRUD analysis
 If you have a business function that
has no entity to CRUD against, then
your data model may be incomplete.
Similarly, if you have entities in your
ERD that are not touched by any
CRUD (there is no business function
that creates, retrieves, updates, or
deletes from it), then you may not
need that entity in your model.
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