Data Modeling

Yong ChoiSchool of Business

CSUB

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Part # 2

Database

Collection of data in electronic format– A digital library of organization

Managed by one set of software that provides access to all the data No data redundancy, data inconsistency,

poor security, application-data dependency...

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Part # 2Database Management System (DBMS)

Database software Act as an interface between

application and physical data files Support centralization of data Independent of specific computer

programs small (MS Access), large/popular

(Oracle)

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Part # 2

Database Models

Hierarchical (Tree) Models Network Model Relational Models

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Part # 2

Relational Database Model In the relational data model the database

is represented as a group of related tables.

The relational data model was introduced in 1970 by E. F. Codd of IBM published a paper in CACM entitled "A Relational Model of Data for Large Shared Data Banks".

It is currently the most popular model. The mathematical simplicity and ease of visualization of the relational data model have contributed to its success.

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Part # 2

Relational Database

A schematic diagram of a relational database (a) and a sample part of a relational database showing different tables (b)

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Part # 2

Relational database and keys A relational database is a collection of

tables that are related to one another based on a common field.

A field, or a collection of fields, is designated as the primary key. The primary key uniquely identifies a record

in the table. When the primary key of one table is

represented in a second table to form a relationship, it is called a foreign key.

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Part # 2

Primary Key Unique identifier

– Last name vs. SS# Prevent confusion Cost of PK

– SS# vs. finger print– Entity Integrity Rule

Any primary key is allowed to accept null values.

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Part # 2

Foreign Key

An attribute in one table whose values must either match the primary key in another table or be null.

The database must not contain any unmatched foreign key values.

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Part # 2Foreign Keys

Student ID

Last Name

First Name

Dorm

2144 Arnold Betty Smith

3122 Taylor John Jones

3843 Simmons Lisa Smith

9844 Macy Bill

2837 Leath Heather Smith

2293 Wrench Tim Jones

Dorm Residence Director

Smith Andrea Fernandez

Jones Daniel Abidjan

Primary Key

Primary Key

Foreign KeyDuplicated from primary key of Major entity(not unique)

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Part # 2

Foreign Keys

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Part # 2Relating tables using a common field

The primary key in the Employer table (EmployerID) is the common field that relates this table to the Position table.

PositionID is the primary key in the Position table. The EmployerID field is a foreign key in this table.

Primary keys can only have one occurrence in a table. Foreign keys may have multiple occurrences.

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Part # 2Why Conceptual Data Modeling is Important?

Effective Communication Tool

User involvement

Independence from a particular

DBMS

Documentation

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Part # 2

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

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. Developed by Peter Chen (1976).

Part # 2ERD using Chen’ Notation

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Part # 2

ER model using IE Notation

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Part # 2Basic Entity Relationship Diagram (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)

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Part # 2

Entity

What should be an Entity: 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)

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Part # 2

Inappropriate entities

System userSystem user System outputSystem output

Appropriate entities

Entity …

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Part # 2

Entity Instance

Entity instance: a single occurrence of an entity.

Student ID

Last Name

First Name

2144 Arnold Betty

3122 Taylor John

3843 Simmons

Lisa

9844 Macy Bill

2837 Leath Heather

2293 Wrench Tim

instance

entity

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Part # 2

“describe the entity’s characteristics” Attributes are represented by an

Ellipse/Oval connected to the entity with a line by Chen’s notation.

Each oval contains the name of the attribute it represents.

Entity: EmployeeAttributes: Employee-Name, Extension, Date-Of-

Hire, Job-Skill-Code

AttributesAttributes

Part # 2ERD using Chen’ Notation

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Part # 2

Classes of attributes

Simple Attribute Composite Attribute Derived Attributes Single-valued Multi-valued Attribute

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Part # 2

How to find entities and attributes??

Entity: a collection of people, places, objects, events, concepts of interest look for nouns Usually, a proper noun is not a good

candidate…. Attribute: property or characteristic of

interest of an entity look for attribute descriptive words

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Part # 2

“attributes that uniquely identify entity instances” Uniquely identify every instance of the

entity Composite identifiers are identifiers that

consist of two or more attributes

Entity: Employee

Identifier: Social-Security-Number

(unique) Identifier(unique) Identifier

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Part # 2

Entities???

ANG Laboratory has several chemists who work on one or more projects. Chemists also may use certain kinds of equipment on each project. The organization would like to store the chemist’s employee identification number, his/her name, up to three phone numbers, his/her project identification number and the date on which the project started. Every piece of equipment, the chemist uses, has a serial number and a cost. Also the organization would like to store the date the chemist was assigned to the project and the date an equipment item was assigned to a particular chemist working on a particular project. A chemist must be assigned at least to one project and one equipment item. Any given equipment item need not be assigned, and a given project need not be assigned either a chemist or an equipment item.

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Part # 2

Entities

Chemist

Project

Equipment

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Part # 2

Attributes???

ANG Laboratory has several chemists who work on one or more projects. Chemists also may use certain kinds of equipment on each project. The organization would like to store the chemist’s employee identification number, his/her name, up to three phone numbers, his/her project identification number and the date on which the project started. Every piece of equipment, the chemist uses, has a serial number and a cost. Also the organization would like to store the date the chemist was assigned to the project and the date an equipment item was assigned to a particular chemist working on a particular project. A chemist must be assigned at least to one project and one equipment item. Any given equipment item need not be assigned, and a given project need not be assigned either a chemist or an equipment item.

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Part # 2

Entities & Attributes

Project

Proj#Start-Date

Chemist

Phone#Emp#

EquipmentSerial#

cost

How many attributes do you (as a entity of our school database) have? – name your attributes

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Part # 2

Example 1: find entities

A department hires many employee. A employee is employed by one department.

A manager manages one department. A department is managed by one manager.

A person must have only one DNA pattern and that pattern must be applied to only one person.

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Part # 2

Example 2: find entities There are several departments in School of

Business and Public Administration at CSUB. Each department belongs to one school. A department has many professors, but a professor may belong to more than one department. Similarly, courses may be offered by several departments and a department must have at least one course. A professor may teach more than one student, and a student may have more than one professor.

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Part # 2Example 4: Find all entities, attributes, and (unique) identifier

The FANTASTIC video rental company has several branches throughout the USA. The data held on each branch is the branch address made up of street, city, state, and zip code, and the telephone number. Each branch is given a branch number, which is unique throughout the company. Each branch is allocated staff, which includes a Manager. The Manager is responsible for the day-today running of a given branch. The data held on a member of staff is his or her name, position, and salary. Each member of staff is given a staff number, which is unique throughout the company. Each branch has a stock of videos. The data held on a video is the catalog number, video number, title, category, daily rental, cost, status, and the names of the main actors, and the director. The catalog number uniquely identifies each video.

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Part # 2Example 4: Find all entities, attributes, and (unique) identifier (con’t)

A customer must first register as a member of a local branch before renting a video tape from any branches. The data held on a member is the first and last name, address, and the date that the member registered at a branch. Each member is given a member number, which is unique throughout all branches of the company. Once registered, a member is free to rent videos, up to maximum of ten at any one time. The data held on each video rented is the rental number, the full name and number of the member, the video number, title, and daily rental, and the dates the video is rented out and date returned. The rental number is unique throughout the company.

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Part # 2

Relationships

Association between entities (by lines) Any connected entities are called participants Operate in both directions

Relationship between Student and Curriculum A student is enrolled in many curriculums. Each curriculum is being studied by many students.

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Part # 2

Relationships ???

ANG Laboratory has several chemists who work on one or more projects. Chemists also may use certain kinds of equipment on each project. The organization would like to store the chemist’s employee identification number, his/her name, up to three phone numbers, his/her project identification number and the date on which the project started. Every piece of equipment, the chemist uses, has a serial number and a cost. Also the organization would like to store the date the chemist was assigned to the project and the date an equipment item was assigned to a particular chemist working on a particular project. A chemist must be assigned at least to one project and one equipment item. Any given equipment item need not be assigned, and a given project need not be assigned either a chemist or an equipment item.

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Part # 2Entities/Relationships& their Attributes

Chemist

Phone#

Project

Proj#Start-Date

Equipment

Works-On

Uses

Date-Assigned

Emp#

Serial#

cost

Assign-Date

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Part # 2

Steps for creating an ERD Develop draft business rules

Using interviews and documents Identify the entities (look for nouns) Identify the attributes (look for attribute descriptive

words) identify draft business rules

Identify the relationships (look for verb or verb phrases between entities)

Identify cardinalities (look for participation related words and phrases such as zero, none, a, one, several, many…..)

Optional (look for auxiliary verbs such as may, might, can and based upon own judgment..)

Set business rules

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Part # 2

Cardinality of Relationship One – to – One (1:1)

Each instance in the relationship will have exactly one related member on the other side

One – to – Many (1:M) A instance on one side of the relationship can have many

related members on the other side, but a member on the other side will have a maximum of one related instance

Many – to – Many (M:N) Instances on both sides of the relationship can have many

related instances on the other side

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Part # 2

1:1 relationship in set notation

DEPARTMT EMPLOYEE

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Part # 2

Example of 1:1 relationship A one-to-one (1:1) relationship is when at most

one instance of a entity A is associated with one instance of entity B.

Each employee has a one’s own office. Cardinality toward the Office entity

Each office is occupied by one employee. Cardinality toward the Employee entity

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Part # 2

1:1 relationship

A person must have one and only one DNA pattern and that pattern must apply to one and only one person.

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Part # 2

1:M relationship in set notation

DEPARTMT EMPLOYEE

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Part # 2

Example of 1:M relationship A one-to-many (1:N) relationships is when for

one instance of entity A, there are zero, one, or many instances of entity B, but for one instance of entity B, there is only one instance of entity A.

Each employee has many offices. Cardinality toward the Office entity

Each office is occupied by one employee. Cardinality toward the Employee entity

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Part # 2

1:M relationshipEach department hires many employees, and each employee is hired by one department.

EMPLOYEEDEPARTMTHIRES

IS_HIRED_BY

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Part # 2

M:N relationship in set notation

WAREHOUSE PRODUCT

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Part # 2

Example of M:N relationship A many-to-many (M:N) relationship, sometimes

called non-specific, is when for one instance of entity A, there are zero, one, or many instances of entity B and for one instance of entity B there are zero, one, or many instances of entity A.

A employee has multiple offices. Cardinality toward the Office entity

A office must be occupied by many employee. Cardinality toward the Employee entity

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Part # 2

M:N relationshipEach student takes many classes, and each class is taken by many students.

** This is not a desirable relationship.**

STUDENTCLASSTAKE

IS_TAKEN_BY

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Part # 2

Complete ER Diagram

Chemist

Phone#

Project

Proj#Start-Date

Equipment

Works-On

Uses

Date-Assigned

N1

N1

Emp#

Serial#

cost

Assign-Date

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Part # 2Cardinality NotationsCardinality Interpretation

Minimum Instances

Maximum Instances

Graphic Notation

Exactly one

Zero or one

One or many

Zero or many

1

1

0

0

1

1

Many (>1)

Many (>1)

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Part # 2

Steps for creating an ERD Develop draft business rules

Using interviews and documents Identify the entities (look for nouns) Identify the attributes (look for attribute descriptive

words) identify draft business rules

Identify the relationships (look for verb or verb phrases between entities)

Identify cardinalities (look for participation related words and phrases such as zero, none, a, one, several, many…..)

Optional (look for auxiliary verbs such as may, might, can and based upon own judgment..)

Set business rules