Critical Success Factors in Database Design
o Work interactively with the users as much as
possible.
Database Design
Methodologies
o Follow a structured methodology throughout the
data modeling process.
o Employ a data-driven approach.
o Incorporate structural and integrity considerations
into the data models.
o Combine conceptualization, normalization, and
transaction validation techniques into the data
modeling methodology.
Database Design Methodology - 1
Critical Success Factors in Database Design
Database Design Methodology - 2
Database Design Methodology
3 main phases:
o Use diagrams to represent as much of the data
models as possible.
o Good documentation of additional data semantics.
o Build a data dictionary to supplement the data
model diagrams.
o Be willing to repeat steps.
o Conceptual database design
Construct a model of the information used,
independent of all physical considerations.
o Logical database design
Construct a model of the information used, based on a
specific data model (e.g. relational), but independent of
a particular DBMS and other physical considerations.
o Physical database design
Produce a description of the implementation of the DB
on secondary storage; it describes the storage
structures and access methods used to achieve
efficient access to the data.
Database Design Methodology - 3
CS3462 Introduction to Database Systems
Helena Wong, 2001
Database Design Methodology - 4
Methodology Overview
Methodology Overview - Conceptual Database Design
Step 1
Build local conceptual data model for each
user view
Step 2
Build and Validate Local Logical Data Model
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 and Implement Security Mechanisms
Step 7
Monitor and Tune the Operational System
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 Specialize/generalize entity types (optional step)
Step 1.7 Draw Entity–Relationship diagram
Step 1.8 Review Local Conceptual Data Model with User
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Methodology Overview –
Logical Database Design for Relational Model
Methodology Overview –
Logical Database Design for Relational Model
Step 2
Step 3
Build and Validate Local Logical Data Model
Build and Validate Global Logical Data Model
Step 2.1 Map Local Conceptual Data Model to Local
Logical Data Model
Step 3.1 Merge Local Logical Data Models into Global
Model
Step 2.2 Derive Relations from Local Logical Data Model
Step 3.2 Validate Global Logical Data Model
Step 2.3 Validate Model using Normalization
Step 3.3 Check for Future Growth
Step 2.4 Validate Model against User Transactions
Step 3.4 Draw Final Entity-Relationship Diagram
Step 2.5 Draw Entity-Relationship Diagram
Step 3.5 Review Global Logical Data Model with Users
Step 2.6 Define Integrity Constraints
Step 2.7 Review Local Logical Data Model with User
Database Design Methodology - 7
CS3462 Introduction to Database Systems
Helena Wong, 2001
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Methodology Overview –
Physical Database Design for Relational Databases
Methodology Overview –
Physical Database Design for Relational Databases
Step 4
Step 6
Translate Global Logical Data Model for Target
DBMS
Step 4.1 Design Base Relations for Target DBMS
Design and Implement Security Mechanisms
Step 6.1 Design User Views
Step 4.2 Design Integrity Rules for Target DBMS
Step 6.2 Design Access Rules
Step 5
Step 7
Design Physical Representation
Monitor and Tune the Operational System
Step 5.1 Analyze Transactions
Step 5.2 Choose File Organization
Step 5.3 Choose Secondary Indexes
Step 5.4 Consider the Introduction of Controlled
Redundancy
Step 5.5 Estimate Disk Space
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Step 1.1 Identify entity types
Branch
Staff
Supervisor
Secretary
Property_for_Rent
Private_Owner
Business_Owner
Step 1.2 Identify relationship types
Advert
Newspaper
Interview
Client
Lease_Agreement
Inspection
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Helena Wong, 2001
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Step 1.2 Identify relationship types
Step 1.2 Identify relationship types
o Branch Has Staff Relationship
o Property_for_Rent DescribedIn Advert relationship
o Staff Manages Property_for_Rent relationship
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o Client Views Property_for_Rent relationship
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Sketch of Supervisor's Local
Conceptual Data Model
Step 1.3 Identify and associate attributes with
entity or relationship types
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CS3462 Introduction to Database Systems
Helena Wong, 2001
Database Design Methodology - 16
Step 1.3 Identify and associate attributes with
entity or relationship types
Step 1.4 Determine attribute domains
o For attributes in the Supervisor’s local conceptual
data model of the DreamHome company.
(e.g. Domain of Branch_No attribute of Branch entity
includes a three-character string, with values
ranging from B1 to B99).
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Step 1.5 Determine candidate and primary key
attributes
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Helena Wong, 2001
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Step 1.6 Specialize / Generalize Entity Types (Optional Step)
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Step 1.6 Specialize / Generalize Entity Types (Optional Step)
Step 1.6 Specialize / Generalize Entity Types (Optional Step)
Additional
Example
Additional
Example
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Step 1.7 Draw Supervisor's Local
Conceptual Data Model
Step 2.1 Map Local Conceptual Data Model to Local Logical
Data Model
To refine the local conceptual data model to remove
undesirable features and to map this model to a local
logical data model:
(a) Remove M:N relationships.
(b) Remove complex relationships.
(c) Remove recursive relationships.
(d) Remove relationships with attributes.
(e) Remove multi-valued attributes.
(f) Re-examine 1:1 relationships.
(g) Remove redundant relationships.
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CS3462 Introduction to Database Systems
Helena Wong, 2001
Removing
data
structures
that are
difficult to
implement
in
relational
databases.
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Removing Advertises M:N Relationship
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Removing Supervises Recursive Relationship
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CS3462 Introduction to Database Systems
Helena Wong, 2001
Removing Leases Complex Relationship
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Removing WorksAt Relationship with
Hours_Worked Attribute
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Removing Tel_No Multi-valued Attribute
Non-Redundant Relationships
A relationship is redundant if the
same information can be obtained
from other relationships.
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An Example Logical Data Model
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Helena Wong, 2001
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Supervisor's local
logical data model
(Version 1)
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Step 2.2 Derive Relations From Local Logical Data Model
Step 2.2 Derive Relations From Local Logical Data Model
o Strong Entity Types: create a relation that includes
all simple attributes.
o 1:1 Relationship Types: post a copy of the primary key
attribute(s) of entity E1 into the E2 relation, to act as a
foreign key. (The indentification of E1 and E2 depends on
the participation constraints)
Eg. Staff(Staff_No, FName, LName, Street, City,
Postcode, Position, Sex, Salary)
Eg. - Staff(Staff_No, Fname, Lname, ..)
o Week Entity Types: create a relation that includes all
simple attributes. In addition, include as a foreign
key the primary key of the owner entity.
- Branch (Branch_No, Address, .., Manager_No),
Foreign Key Manager_No references Staff(Staff_No)
Eg. Next-of-Kin (Staff_No, NName, Address, Tel_No,
Relationship), Foreign key Staff_No references
Staff(Staff_No)
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Step 2.2 Derive Relations From Local Logical Data Model
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Step 2.2 Derive Relations From Local Logical Data Model
o Superclass/subclass relationships:
o 1:M Relationship Types of E1 to E2: post a copy of
the primary key attribute(s) of entity E1 into the E2
relation, to act as a foreign key.
Eg. – Branch (Branch_No, Address, ..)
– Staff (Staff_No, Fname, .. Branch_No),
Foreign Key Branch_No references Branch
(Branch_No)
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CS3462 Introduction to Database Systems
Helena Wong, 2001
Example 1:
All_Property(Property_No, Address, Type, Rent, Price)
Example 2:
Property_For_Rent(Property_No, Address, Type, Rent)
Property_For_Sale(Property_No, Address, Type, Price)
Example 3:
Property(Property_No, Address, Type)
Property_For_Rent(Property_No, Rent), Foreign Key
Property_No references Property(Property_No)
Property_For_Sale(Property_No, Price), Foreign Key
Property_No references Property(Property_No)
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Step 2.3 Validate Model using Normalization
To ensure that each relation derived from the logical
data model is in at least Boyce-Codd Nornal Form.
Issues:
o A normalized design organizes the data according to
its functional dependencies => lies somewhere
between conceptual and physical design
o The logical design may not be the final design. Eg.
some normalized relations are denormalized in the
physical design.
Step 2.4 Validate Model Against User Transactions
To ensure that the logical data model supports the
transactions that are required by the user view.
Example transactions
(a) Insert details for new members of staff.
(b) Delete details of a member of staff, given the staff
number.
o Normalization forces us to understand completely
each attribute.
o A normalized design is free of update anomalies, and
the DB can be easily extended.
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Supervisor's local
logical data model
displaying the
transactions supported
Step 2.5 Draw
Supervisor's local
logical data model
(Final Version)
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CS3462 Introduction to Database Systems
Helena Wong, 2001
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Step 3.1 Merge Local Logical Data Models into
Global Models
Comparison of entities and their primary keys in
Supervisor’s and Manager’s views
(a) Review the names of entities and their primary keys.
(b) Review the names of relationships.
(c) Merge entities from the local views.
(d) Include (without merging) entities unique to each local view.
(e) Merge relationships from the local views.
(f) Include (without merging) relationships unique to each local
view.
(g) Check for missing entities and relationships.
(h) Check foreign keys.
(i) Check Integrity Constraints.
(j) Draw the global logical data model.
(k) Update the documentation.
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Comparison of relationships in Supervisor’s and
Manager’s views
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Helena Wong, 2001
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Merging the Staff entities from Supervisor's and
Manager's views
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Merging the Advert entities from Supervisor's and
Manager's views
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Step 3.4 Draw Global logical
data model of DreamHome
case study
Step 3.1 Merge Local Logical Data Models into
Global Models
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Physical Database Design (Steps 4-7)
o Sources of information for the physical design
process includes global logical data model and
documentation that describes model.
o Logical database design is concerned with the what,
physical database design is concerned with the how.
o Physical Database Design is the process of producing
a description of the implementation of the database on
secondary storage.
o Describes the storage structures and access methods
used to achieve efficient access to the data.
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CS3462 Introduction to Database Systems
Helena Wong, 2001
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Step 4 Translate Global Logical Data Model for Target DBMS
Step 5 Design Physical Representation
o Typical Disk Configuration
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Step 5.1 Analyze transactions
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ER Model for Sample Transactions showing
Expected Occurrences
Example - Sample Transactions
(A)
Insert details for a new member of staff, given
the branch address.
(B)
List rental properties handled by each staff
member at a given branch address.
(C)
Assign a rental property to a member of staff,
checking that a staff member does not manage
more than 10 properties already.
(D)
List rental properties handled by each branch
office.
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Helena Wong, 2001
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Transaction Usage Map for Sample Transactions
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Analysis of Selected Transaction B
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CS3462 Introduction to Database Systems
Helena Wong, 2001
Analysis of Selected Transaction A
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Analysis of Selected Transaction C
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Step 5.4 Consider introducing controlled redundancy
Example 1:
Example 2: Combined renter and interview relations
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Step 5.4 Consider introducing controlled redundancy
Example 2: Duplicating LName attribute in the
Property_for_Rent relation
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CS3462 Introduction to Database Systems
Helena Wong, 2001
Step 5.4 Consider introducing controlled redundancy
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Step 5.5 Estimate disk space requirements
o Lookup Table for Property_Type Attribute
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Step 5.5 Estimate disk space requirements
o Comparison of Space Requirements for
Property_for_Rent Relation
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CS3462 Introduction to Database Systems
Helena Wong, 2001