1. IST 318 Database Administration
Lecture 4
Data Modeling

2. Topics
Entities
Relationship
Attributes and keys
Normalization

3. Data Modeling Data modeling is trying to answer the WHAT questions
What data items are needed?
What are the relationships between these items?
Data modeling is critical in database design
Starting from collecting data requirements
Providing a conceptual model of entities & relationships essential for communication and understanding
A blueprint to build the physical database

4. Benefits of a Sound Data Model
Minimum data redundancy
Maximum data integrity
Better data sharing
Increased consistency
More timely access to data: performance
Better data usability: overall
Additional benefits
New usages
Data mining  find out patterns hidden in normal data

5. Three Rules to Follow Don’t think process; think structure
Don’t think physical; think conceptual
Focus on requirement from business perspective
Avoid getting down to details such as storage issues and DBMS constraints
Don’t think process; think structure
The main point is to answer what need to be stored and what is the right way to represent the interrelationships
Not when and how they are used
Don’t think navigation; think relationship
Focus on compiling the dictionary, don’t worry about in how many different ways it can be used
Several constraints have been used for data integrity purposes:
Primary key: means not null and unique.
Not null: a valid pet_type value is needed for any record.
check (pet_sex_flag_mf in (‘M’, ‘F’)): only the two specific values (M and F) are allowed
The data type char is selected for pet_sex_flag_mf, since its length is fix to 1.

6. Entities and Entity Occurrences
Entity (also known as entity set)
Similar to the concept of class
Real-world or conceptual concepts that can be described via a number of attributes
A template of entities of the same kind
Examples: employee, department, location
Entity occurrences (a simple entities)
Similar to the concept of object
Instances of certain types (or entity sets)
Examples: Craig Mullin, Administrative, location #1

7. Attributes An attribute is a characteristic of an entity
An attribute does one of the three things
Identifies: uniquely identify a record
Candidate key
Becomes primary key when chosen
Should be immutable
Relates: link to an occurrence in another entity
Foreign key
Describes: depicts or express a characteristic of an entity occurrence
The salary attribute of the employee entity

8. Keys Candidate keys Primary keys Foreign keys
Sometimes it’s possible that more than sets of attributes can uniquely identify an occurrence of an entity
Example:
Both SSN and StudentId in the entity STUDENT
(StudentId,LastName,FirstName,SSN, ...)
Primary keys
The one chosen from a set of candidate keys
Foreign keys
Identify a relationship between entity occurrences in two entities

9. Relationships Defines how different entities relate to each other
The keys define a relationship: PK-FK
Naming Relationships
Example: between COURSE and INSTRUCTOR
Entities are nouns/noun phrases
Relationships are verbs/verb phrases
COURSE
INSTRUCTOR
is-taught-by

10. Cardinality and Optionality
The number of occurrences that can exist between a pair of entities
Each end of a relationship has a cardinality
Also known as degree
Typical cardinality terms: one, many
Optionality
Whether relationships are mandatory or optional
Each end of a relationship has a optionality characteristic

11. An Example In the employed-by relationship
The STORE can have 0, 1, or many EMPLOYEEs
If an EXPLOYEE exists, a relationship to a STORE is mandatory
EMPLOYEE
STORE
Employed by

12. Three Levels Logical data model Physical data model
Conceptual data model
Depict a high-level, business-oriented view of information
Logical data model
Offers a comprehensive formal structure that serves as a blueprint for business data
Physical data model
Transfers the logical data model into a physical implementation using a specific DBMS

13. Normalization

14. Normalization – first normal form
form eliminates
repeating
groups and
nonatomic data
from an entity

15. Normalization – second normal form
Second normal form ensures that all the attributes of each entity are dependent

16. Normalization – third normal form
Third normal form ensures that no relationships between attributes exist within an entity