Logical Data Modeling - Data Modeling for MongoDB - page 130

Emp
Id

Dept
Cd

Emp
Name

Emp Start
Date

Emp Vested
Ind

Phone 1 Phone 2 Phone 3 Dept Name

Henry
Winkler

123 A 973-555-1212 678-333-3333 343-222-1111 Data Admin N

4/1/2012

Steve
Martin

789 A 732-555-3333 678-333-3333 343-222-1111 Data Admin Y

3/5/2007

Mary
Smith

Data Ware-
house

565 B 333-444-1111 516-555-1212 343-222-1111 Y

2/25/2006

744 A 232-222-2222 678-333-3333 343-222-1111 Bob Jones Data Admin N

5/5/2011

First Normal Form (1NF)
Recall that the series of rules can be summarized as: Every attribute is single-valued and
provides a fact completely and only about its primary key . First Normal Form (1NF) is the
“single-valued” part. It means that for a given primary key value, we can find, at most, one
of every attribute that depends on that primary key.

Ensuring each attribute provides a fact about its primary key includes addressing repeating
groups and multi-valued attributes. Specifically, the modeler needs to:

• Move repeating attributes to a new entity . When there are two or more of the

same attribute in the same entity, they are called repeating attributes. The reason
repeating attributes violate 1NF is that for a given primary key value, we are get-
ting more than one value back for the same attribute. Repeating attributes often
take a sequence number as part of their name, such as phone number in this em-
ployee example. We can find ourselves asking many questions just to determine
if there are any repeating attributes we need to address. We can have a question
template such as “Can a [[insert entity name here]] have more than one [[insert at-
tribute name here]]?” So these are all valid questions in our employee example:

•

Can an Employee have more than one Employee Identifier ?

•

Can an Employee have more than one Department Code ?