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MIS 340: Data Modeling 1. Yong Choi School of Business CSUB. 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

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mis 340 data modeling 1

MIS 340:Data Modeling 1

Yong Choi

School of Business

CSUB

study objectives
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
why data modeling
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
conceptual data modeling
Conceptual 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.
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.
basic erd elements
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)
chen s notation
Chen’s Notation
  • Entities
    • rectangle containing the entity’s name.
  • Attributes
    • oval containing the attribute’s name.
  • Relationships
    • diamond containing the relationship’s name.
steps for creating an erd
Steps for creating an ERD
  • Identify entities
  • Identify attributes
  • Identify relationships
entity
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)
entity instance
Entity Instance

Entity instance: a single occurrence of an entity.

  • 6 instances

Entity: student

instance

attributes
Attributes

“describe property or characteristic of an entity”

  • Entity: Employee
  • Attributes:
    • Employee-Name
    • Address (composite)
    • Phone Extension
    • Date-Of-Hire
    • Job-Skill-Code
    • Salary
classes of attributes
Classes of attributes
  • Simple attribute
  • Composite attribute
  • Derived attributes
  • Single-valued attribute
  • Multi-valued attribute
simple composite attribute
Simple/Composite attribute
  • 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
derived attribute
Derived attribute
  • 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)
single valued attribute
Single-valued attribute
  • 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
multi valued attributes
Multi-valued attributes
  • can have many values.
    • Examples:
      • A person may have several college degrees.
      • A household may have several phones with different numbers
      • A car color
example movie database
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)
how to find entities
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….
how to find attributes
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)
unique identifier
(unique) Identifier

“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)