Chapter 8
Methodology - Methodology -
Conceptual Database DesignConceptual Database Design
Chapter 15 in Textbook
2
Design MethodologyDesign Methodology
A structured approach that uses procedures, techniques, tools,
and documentation aids to support and facilitate the process of
design.
Conceptual DB Design
3
Database DesignDatabase Design
Physical DB design
LogicalDB design
ConceptualDB design
Hardware dependentSoftware dependent
Hardware independentSoftware dependent
Hardware independentSoftware independent
Conceptual DB Design
4
Success Factors in Database Success Factors in Database DesignDesign
• Work interactively with users as much as possible.
• Follow a structured methodology throughout the data modelling process.
• Employ a data-driven approach.
• Incorporate structural and integrity considerations into the data models.
• Combine conceptualization, normalization, and transaction validation techniques into the data modelling methodology.
• Use diagrams to represent as much of the data models as possible.
• Build a data dictionary to supplement the data model diagrams.
• Be willing to repeat steps.
Conceptual DB Design
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Design Methodology OverviewDesign Methodology Overview
Step 1 Build local conceptual data model for each user view.
Step 2 Build and validate local logical data model for each view.
Step 3 Build and validate global logical data model.
Step 4 Translate global logical data model for target DBMS.
Step 5 Design physical representation.
Step 6 Design user views.
Step 7 Design security mechanisms.
Step 8 Consider the introduction of controlled redundancy.
Step 9 Monitor and tune the operational system.
Conceptual DB Design
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Methodology Overview – Methodology Overview – Conceptual Database DesignConceptual Database Design
Step 1 Build local conceptual data model for each user view
Step 1.1 Identify entity types.
Step 1.2 Identify relationship types.
Step 1.3 Identify and associate attributes with entity or relationship types.
Step 1.4 Determine attribute domains.
Step 1.5 Determine candidate and primary key attributes.
Step 1.6 Consider use of enhanced modeling concepts (optional step).
Step 1.7 Check model for redundancy.
Step 1.8 Validate local conceptual model against user transactions.
Step 1.9 Review local conceptual data model with user.
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Methodology Overview – Methodology Overview – Logical Database Design for Logical Database Design for
Relational ModelRelational Model
Step 2 Build and validate local logical data model for each view
Step 2.1 Derive relations for local logical data model.
Step 2.2 Validate relations using normalization.
Step 2.3 Validate relations against user transactions.
Step 2.4 Define integrity constraints.
Step 2.5 Review local logical data model with user.
Conceptual DB Design
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Methodology Overview – Methodology Overview – Logical Database Design for Logical Database Design for
Relational ModelRelational Model
Step 3 Build and validate global logical data model
Step 3.1 Merge local logical data models into global model.
Step 3.2 Validate global logical data model.
Step 3.3 Check for future growth.
Step 3.4 Review global logical data model with users.
Conceptual DB Design
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Methodology Overview – Methodology Overview – Physical Database Design for Physical Database Design for
Relational ModelRelational Model Step 4 Translate global logical data model for target DBMS
Step 4.1 Design base relations.
Step 4.2 Design representation of derived data.
Step 4.3 Design enterprise constraints.
Step 5 Design physical representation
Step 5.1 Analyze transactions.
Step 5.2 Choose file organization.
Step 5.3 Choose indexes.
Step 5.4 Estimate disk space requirements.
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Methodology Overview – Methodology Overview – Physical Database Design for Physical Database Design for
Relational ModelRelational Model
Step 6 Design user views
Step 7 Design security mechanisms
Step 8 Consider the introduction of controlled redundancy
Step 9 Monitor and tune the operational system
Conceptual DB Design
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Step 1Step 1 Build Local Conceptual Build Local Conceptual Data Model for Each ViewData Model for Each View
Objective: To build a local conceptual data model of an enterprise for each
specific view.
Step 1.1 Identify entity types
Objective: To identify the main entity types that are required by the view;
Document entity types in data dictionary.
Conceptual DB Design
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Data Dictionary for Staff View Data Dictionary for Staff View ShowingShowing Description of EntitiesDescription of Entities
Entity Name Description Aliases Occurrence
Staff General term describing all staff Employee Each member of staff works at one
employed by DearmHome particular branch
PropertyForRent General term describing all Property Each property has a single owner &
property for rent is available at one specific branch,
where the property is managed by 1
member of staff. A property is viewed
by many clients and rented by a single
client at a time
Conceptual DB Design
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Step 1Step 1 Build Local Conceptual Build Local Conceptual Data Model for Each ViewData Model for Each View
Step 1.2 Identify relationship types
Objective: To identify the important relationships that exist between the
entity types that have been identified.
– Check for binary, complex, recursive relationship types.
– Check for explicit, and implicit relationship types.
– Use ER diagrams.
– Determine multiplicity of relationships.
– Check for fan and chasm traps.
– Check that each entity participate in at least one relationship.
– Document relationship type.
Conceptual DB Design
ERD for Staff View of ERD for Staff View of DreamHomeDreamHome
BUSINESSOWNER
STAFF
PROPERTY
PRIVATEOWNER
LEASE
CLIENT
PREFERENCE
POwn
holdassociate
manage
state
supervise register
BOwn
(1:1)
(1:1)
(1:1)
(1:1)
(1:1)
(0,*) (0,*)
(0,*)
(0,*)
(0,*)
(0,1)
(1,*)
(1,*)
(0,1)
(0,1)
(0,100)
views (0,*)(0,*)
supervisor
supervisee
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Data Dictionary for Staff View Data Dictionary for Staff View Showing Description of RelationshipsShowing Description of Relationships
Entity Name Multiplicity Relationship Entity Name Multiplicity
Staff 0..1 Manages PropertyForRent 0..100
0..1 Supervises Staff 0..10
PropertyForRent 1..1 AssociatedWith Lease 0..*
Conceptual DB Design
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Step 1Step 1 Build Local Conceptual Build Local Conceptual Data Model for Each ViewData Model for Each View
Step 1.3 Identify and associate attributes with entity or relationship types
Objective: To identify and associate attributes with the appropriate entity or
relationship types and document the details of each attribute.
For entity list what information are we required to hold on?
–Check simple & composite attributes.
–Check single & multi-valued attributes.
–Derived attributes.
–Check for shared attributes.
–Document the attribute.
Conceptual DB Design
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Step 1Step 1 Build Local Conceptual Build Local Conceptual Data Model for Each ViewData Model for Each View
Step 1.4 Determine attribute domains
Objective: To determine domains for the attributes in the local conceptual model and document the details of each domain.
–Data type.
–Size.
–Allowable value.
–Default value.
Conceptual DB Design
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Data Dictionary for Staff View Data Dictionary for Staff View Showing Description of AttributesShowing Description of Attributes
Entity Attribute Description Data Length Nulls Multi- Default Range PKName Type Valued Value
Staff StaffNo Uniquely identifies a staff member varchar 5 No No Y
name
FName First name of Staff varchar 15 No No
Lname Last name of Staff varchar 15 No No
position Job title of member of staff varchar 10 No No
sex Gender of member of staff character 1 Yes No M F, M
DOB Date of Birth of member of staff Date Yes No 1960-1990
Conceptual DB Design
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Step 1Step 1 Build Local Conceptual Build Local Conceptual Data Model for Each ViewData Model for Each View
Step 1.5 Determine candidate and primary key attributes
Objective: To identify the candidate key(s) for each entity and if there is more than
one candidate key, to choose one to be the primary key.
CK must be:
– minimal set of attributes.
– least likely to have its value changed.
– fewest size or smallest maximum number.
– easiest to use from the user’s point of view.
Step 1.6 Consider use of enhanced modeling concepts
Objective: To consider the use of enhanced modeling concepts, such as
specialization / generalization, aggregation, and composition.
Conceptual DB Design
ERD with PKERD with PK
BUSINESSOWNER
STAFF
PROPERTY
PRIVATEOWNER
LEASE
CLIENT
PREFERENCE
POwn
holdassociate
manage
state
supervise register
BOwn
(1:1)
(1:1)
(1:1)
(1:1)
(1:1)
(0,*) (0,*)
(0,*)
(0,*)
(0,*)
(0,1)
(1,*)
(1,*)
(0,1)
(0,1)
(0,100)
views (0,*)(0,*)
supervisor
supervisee
OwnerNo
OwnerNo
LeaseNo
StaffNo
PropertyNo
ClientNo
CommentVDate
EERD for Staff View of EERD for Staff View of DreamHomeDreamHome
BUSINESSOWNER
STAFF
PROPERTY
PRIVATEOWNER
LEASE
CLIENT
PREFERENCE
holdassociate
manage
state
register
BOwn
(1:1)
(1:1)
(1:1)
(1:1)
(1:1)
(0,*) (0,*)
(0,*)
(1,1)(1,*)
(0,1)
(0,100)
views (0,*)(0,*)
OwnerNo
LeaseNo
StaffNo
PropertyNo
ClientNo
CommentVDate
OWNER
d
SUPERVISOR
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Step 1Step 1 Build Local Conceptual Build Local Conceptual Data Model for Each ViewData Model for Each View
Step 1.7 Check model for redundancy
Objective: To check for the presence of any redundancy in the model.
1. Re-examine 1:1 relationships.
2. Remove redundant relationships.
Step 1.8 Validate local conceptual model against user transactions
Objective: To ensure that the local conceptual model supports the transactions required by the view.
–Describe the transaction.
–Use transaction pathways: diagrammatically represent the pathway taken by each transaction on the ERD.
Conceptual DB Design
Using transaction’s PathwaysUsing transaction’s Pathways
BUSINESSOWNER
STAFF
PROPERTY
PRIVATEOWNER
LEASE
CLIENT
PREFERENCE
holdassociate
manage
state
register
BOwn
(1:1)
(1:1)
(1:1)
(1:1)
(1:1)
(0,*) (0,*)
(0,*)
(1,1)(1,*)
(0,1)
(0,100)
views (0,*)(0,*)
OwnerNo
LeaseNo
StaffNo
PropertyNo
ClientNo
CommentVDate
OWNER
d
SUPERVISOR(a)
(e)(d)
(h,i)
(j)
(l)
(c,g)
(m)
(k)
(b)
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Step 1Step 1 Build Local Conceptual Build Local Conceptual Data Model for Each ViewData Model for Each View
Step1.9 Review local conceptual data model with user
Objective: To review the local conceptual data model with the user to ensure that the model is a ‘true’ representation of the user’s view of the enterprise.
Conceptual DB Design
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