MIS 340:Data Modeling 1

Yong ChoiSchool of Business

CSUB

Part # 2

2

Study Objectives Understand concepts of data modeling and

its purpose Learn how relationships between entities are

defined and refined, and how such relationships are incorporated into the database design process

Learn how ERD components affect database design and implementation

Learn how to interpret the modeling symbols

Part # 2

3

Why Data Modeling? Represent “reality” of the actual database Blue print: documentation Effective Communication Tool User involvement Represent abstraction of requirements Identify the business rules to be stored in

the database Independence from a particular DBMS

Part # 2

4

Conceptual data modelingConceptual data modeling

The conceptual data modeling revolves around discovering and analyzing organizational and users data requirements (see the supplement).

What data is important What data should be maintained

The major activity of this phase is identifying entities, attributes, and their relationships to construct model using the Entity Relationship Diagram methodology.

Part # 2

5

Entity Relationship diagram (ERD) Entity Relationship diagram (ERD)

Data modeling methodology Developed by Peter Chen (1976).

See his original ERD article on the class website

ERD is commonly used to: Translate different views of data among managers,

users, and programmers to fit into a common framework.

Define data processing and constraint requirements to help us meet the different views.

Help implement the database.

Part # 2

6

Basic ERD Elements

Entity : a collection of people, places, objects, events, concepts of interest (a table)

Entity instance – a member of the Entity : a person, a place, an object … (a row in a table)

Attribute - property or characteristic of interest of an entity (a field in a table)

Relationship – association between entities (corresponds to primary key-foreign key equivalencies in related tables)

Part # 2ERD using Chen’ Notation (first - original)

Part # 2

8

Chen’s NotationChen’s Notation

Entities rectangle containing the entity’s name.

Attributes oval containing the attribute’s name.

Relationships diamond containing the relationship’s

name.

Part # 2

9

Steps for creating an ERD

1. Identify entities2. Identify attributes 3. Identify relationships

Part # 2

10

Entity

“A fundamental THING of relevance to the enterprise about which data may be kept”

What should be an Entity: both tangible & intangible

An object that will have many instances in the database An object that will be composed of multiple attributes An object that we are trying to model

What should NOT be an Entity: A user of the database system An output of the database system (e.g. a report)

Part # 2

11

ERD using IE Notation (most popular)

Part # 2

12

Entity InstanceEntity instance: a single occurrence of an entity.

6 instances

Student ID

Last Name

First Name

2144 Arnold Betty

3122 Taylor John

3843 Simmons Lisa

9844 Macy Bill

2837 Leath Heather

2293 Wrench Tim

Entity: student

instance

Part # 2

13

Entity Instance (con’t)

Part # 2

14

“describe property or characteristic of an entity ” Entity: Employee Attributes:

Employee-Name Address (composite) Phone Extension Date-Of-Hire Job-Skill-Code Salary

AttributesAttributes

Part # 2

15

Classes of attributes

Simple attribute Composite attribute Derived attributes Single-valued attribute Multi-valued attribute

Part # 2

16

A simple attribute cannot be subdivided. Examples: Age, Gender, and Marital status

A composite attribute can be further subdivided to yield additional attributes. Examples:

ADDRESS -- Street, City, State, Zip PHONE NUMBER -- Area code, Exchange

number

Simple/Composite attributeSimple/Composite attribute

Part # 2

17

is not physically stored within the database instead, it is derived by using an algorithm.

Example: AGE can be derived from the date of birth and the current date.

MS Access: int(Date() – Emp_Dob)/365)

Derived attributeDerived attribute

Part # 2

18

can have only a single (atomic) value. Examples:

A person can have only one social security number. A manufactured part can have only one serial

number. A single-valued attribute is not

necessarily a simple attribute. Part No: CA-08-02-189935 Location: CA, Factory#:08, shift#: 02, part#: 189935

Single-valued attribute Single-valued attribute

Part # 2

19

can have many values. Examples:

A person may have several college degrees. A household may have several phones with

different numbers A car color

Multi-valued attributesMulti-valued attributes

Part # 2

20

Example - “Movie Database”

Entity: Movie Star

Attributes: SS#: “123-45-6789” (single-valued) Cell Phone: “(661)123-4567, (661)234-5678” (multi-

valued) Name: “Harrison Ford” (composite) Address: “123 Main Str., LA, CA” (composite) Birthdate: “1-1-50” (simple) Age: 50 (derived)

Part # 2

21

How to find entities? Entity:

A fundamental THING of relevance to the enterprise about which data may be kept: things acted on by business activities

people, places, objects, events…. Tangible: customer, product intangible (active/conceptual): equipment breakdown look for nouns (beginner) BUT a proper noun is not a good

candidate….

Part # 2

22

How to find attributes? Attribute:

property or characteristic of an entity A descriptor whose values are associated with

individual entities of a specific entity type look for descriptions, characteristics, and properties of

entity (beginner)

Part # 2

23

“attributes that uniquely identify entity instances” Uniquely identify every instance of the entity One or more of the entity’s attributes

Composite identifiers are identifiers that consist of two or more attributes

Identifiers are represented by underlying the name of the attribute(s)Employee (employee_ID), student (student_ID)

(unique) Identifier(unique) Identifier