Data Modeling 1

Yong ChoiSchool of Business

CSUB

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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

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Data Model and Data Modeling

Model: an abstraction of a real-world object or event Useful in understanding complexities of the

real-world environment Data model

Relatively simple representations of complex real-world data structures

Data modeling is iterative and progressive process

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Data Model by Access

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Part # 2Data Model by Peter Chen’ Notation (first - original)

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Data modelingData modeling The data modeling revolves around

discovering and analyzing organizational and users data requirements based on business rules.

Identify what data is important Identify 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.

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Data Model Basic Building Blocks Entity : anything about which data are to

be collected and stored Attribute: a characteristic of an entity Relationship: describes an association

among entities One-to-many (1:M) relationship Many-to-many (M:N or M:M) relationship One-to-one (1:1) relationship

Constraint: a restriction placed on the data

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The Importance of Data Model Blue print: documentation Facilitate interaction among the

managers, the designer, and the end user Effective Communication Tool User involvement

Independence from a particular DBMS

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Business Rules Descriptions of policies, procedures, or

principles within a specific organization Use for discovering and analyzing

organizational and users data requirements for the data model

Use for describing characteristics of data Allow designer to understand business

processes Allow designer to develop appropriate

relationship participation rules and constraints

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Discovering Business Rules Sources of business rules:

Top management (policy makers) and managers

Written documentation Procedures Standards Operations manuals

Direct interviews with end users

Part # 2Translating Business Rules into Data Model Components

Nouns translate into entities Verbs translate into relationships among entities

Relationships are bidirectional Two questions to identify the relationship type:

How many instances of B are related to one instance of A? How many instances of A are related to one instance of B?

Example relationship between student and class: In how many classes can one student enroll? – many classes How many students can enroll in one class? – many students

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Business Rules Example 1 A professor can

teach many classes and each class is taught by one professor.

A professor can advise many students and each student is advised by one professor.

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Business Rules Example 2

Each sales representative writes many invoices and each invoice is written by one sales representative.

Each sales representative is assigned to many department and each department has one at most one sales representative.

Each customer can generate many invoices and each invoice is generated by one customer.

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Entity Relationship diagram (ERD) Entity Relationship diagram (ERD) Data modeling methodology Developed by Peter Chen (1976).

Entity : anything about which data are to be collected and stored

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)

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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

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Most popular ERD Notation (very minor differences with our textbook)

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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

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Entity Instance (con’t)

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Entity Type and Entity InstancesEntity Type and Entity Instances

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“Describe characteristics of an entity ” Entity: Employee Attributes:

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

AttributesAttributes

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Classes of attributes

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

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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

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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

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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

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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

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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)

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How to find entities? Entity:

A fundamental thing of relevance to the organization about which data may be kept

people, places, objects, events…. Tangible: customer, product Intangible: order, invoice look for nouns (beginner) BUT a proper noun is

not a good candidate….

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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 characteristics of entity

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“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

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Practice

Try Practice 1 – 4 from Data Modeling Practice slide from week 6 – class website.

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