2. • The process of developing database structures
user requirements for data
• a structured methodology
Structured Methodology - a number of ordered formal
processes with known inputs and expected outputs
Objectives
1. derive relationships
2. evolve to meet user requirements
3. Do it right the first time!
Database Design
3. · Reduce data redundancy.
· Provide stable data structures that can be readily
changed with changing user requirements.
· Allow users to make ad hoc requests for data.
· Maintain complex relationships between data
elements.
· Support a large variety of decision needs
Database Design Goals
4. • data availability
• data reliability
• data currency
• data consistency
• data flexibility
• data efficiency
Verify these criteria are satisfied via technical review
Database Design
5. • 3 types of data objects:
– Entities
– Attributes
– Relationships
• ENTITIES: Are persons, places, or things about which data is
to be, or is, gathered
• ATTRIBUTES : Are the properties of entities.
Examples are Names, Tax Numbers, Age, Status
• RELATIONSHIPS : Describe how entities relate to each other
eg Customers BUY Products
– Persons WORK_ON Jobs
Logical Data Modeling
6. •Are persons, objects or events about which
information is, or will be, recorded in the Database
•The designation of a ‘thing’ about which data is to be
collected, stored or processed.
•Many of these Entities can be identified with
Business Activities (e.g. suppliers, purchase orders,
customer)
Entities...
7. Designing a database involves choosing:
1. The tables that belong in the database.
What are the entities?
2. The columns that belong in each table.
What are the properties?
3. How tables and columns interact with each other.
What do they have in common?
3 Steps in Design
8. Physical
Level Design
Final Information
Level Design
Functional
Requirements
Information Level
Design Processes
Physical
Constraints
Final Database
Structure
Other matters
Domains, Nulls,
Derived Data,
Encoded Data.
Data Base Model
Database Design
9. 2 entities can be related as :
One to One : (1 : 1)
The interpretation of this is that an occurrence of an entity ‘A’
can relate to ONE and ONLY ONE occurrence of entity ‘B’, and
an occurrence of entity ‘B’ can relate to ONE and ONLY ONE
occurrence of entity ‘A’
One to Many : (1: N)
The interpretation is that ONE occurrence of entity ‘A’ can
relate to ONE or MORE occurrences of entity ‘B’, but an
occurrence of entity ‘B’ can relate to ONE ONLY occurrence of
entity ‘A’
Logical Data Modeling
10. Many to Many (N : N) - a common business
relationship
The interpretation is that ONE or MORE occurrences
of entity ‘A’ can relate to ONE or MORE occurrences
of entity ‘B’ and ONE or MORE occurrences of entity
‘B’ can relate to ONE or MORE occurrences of entity
‘A’
Logical Data Modeling
11. Type Shown As Example
One to One 1:1 Book -----> Title
One to Many 1:N Publisher ----
>Books
Many to Many N:N Books <---
>Authors
Entity Relationships
12. Normalization
Normalization is the process of organizing
data in a database. This includes creating
tables and establishing relationships
between those tables according to rules
designed both to protect the data and to
make the database more flexible by
eliminating two factors: redundancy and
inconsistent dependency.
14. First Normal Form
• Eliminate repeating groups in individual
tables.
• Create a separate table for each set of
related data.
• Identify each set of related data with a
primary key.
15. No Repeating Groups
Student# Advisor Adv-Room Class#
---------------------------------------
1022 Jones 412 101-07
1022 Jones 412 143-01
1022 Jones 412 159-02
4123 Smith 216 201-01
4123 Smith 216 211-02
4123 Smith 216 214-01
16. Second Normal Form
• Create separate tables for sets of values
that apply to multiple records.
• Relate these tables with a foreign key.
17. Eliminate Redundant Data
The following two tables demonstrate second normal form:
Students: Student# Advisor Adv-Room
------------------------------
1022 Jones 412
4123 Smith 216
Registration: Student# Class#
------------------
1022 101-07
1022 143-01
1022 159-02
4123 201-01
4123 211-02
4123 214-01
19. Eliminate data not dependant
on key
Students: Student# Advisor
-------------------
1022 Jones
4123 Smith
Faculty: Name Room Dept
--------------------
Jones 412 42
Smith 216 42
20. A database which will:
• Accurately reflect the ‘real world’ data in all
required aspects
• Be responsive to Management information demands
• Reflect Business Rules and Controls
• Be capable of modification to meet changes
in Management needs
• Be an asset to the Organization/Enterprise
End Product of Data Base
Design
