IT 21103/41103 System Analysis & Design

Chapter 04 Data Modeling

Concerned with the data flow of an organization

Data Modeling Focuses on Data Only

Data Modeling Data Attributes NameSizeType

Data Modeling Name Unique Indentifer

Data Modeling Size Amount of space required to hold the data

Data Modeling Type How the computer stores the data

Data Modeling Data Structures Specific organizational strategies for associating data elements

Data Modeling Examples:Receipts File Folders

Data Modeling Computer Data Structures Mimic the real-world Helps the analyst link data to the new system

Data Modeling Data Streams Series of characters that form a command or represent specific data values in a program

Data Modeling File Organized data structure with a specific format

Data Modeling Master File Identifies an individual person or thing in the organization

Data Modeling Transaction File Data collection that represents a specific event or activity

Data Modeling Database Collection of files containing data about the current operations of an organization

Data Modeling Data Warehouse Collection of files about the past operations of an organization

Data Modeling Relational Databases Collection of data tied together by common fields

Data Modeling Common Fields Primary Key Field(s) Foreign Key Field(s) - Create Relationships

Data Modeling Entity-Relationship Diagram - ERD

ERD ► The Entity-Relationship Approach  Represents reality using well-defined graphics and rules ► Basic building blocks are “things” (entities) and relationships Member Animal M 1 Adopts

ERD ► Advantages  Theoretical foundation (Set Theory)  Good for communication  Build E-R Model, then translate to any type of RDBMS ► Disadvantages  Different (yet another new thing to learn)  Must translate to the relational model

ERD ► Entity-Relationship Model: Basic Concepts  Entity ► Thing, Object, Concept of interest to the enterprise ► Each occurrence can be uniquely identified

ERD ► Entity-Relationship Model: Basic Concepts  Attribute ► Property of an entity ► Column

ERD ► Entity-Relationship Model: Basic Concepts  Relationship ► Association between two (or more) entities

ERD ► Entity-Relationship Model: Basic Concepts  Entity Identifier ► Attribute(s) whose value uniquely identifies an entity ► Primary Key

ERD ► What is an Entity?  Physical entity types ► Person ► Building ► Machine ► Book ► Usually Singular

ERD ► What is an Entity?  Conceptual entity types ► Contract ► Account ► Order ► Course

ERD ► What is an Entity?  Event entity types ► Transaction ► Shipment ► Reservation ► Phone Call ► Seminar Offering

ERD ► Entity-Relationship Model: Diagrams  Example:  Soft Rectangle represents entities ► Noun ► Singular  Connecting Line represents relationships ► Verb Member Animal Adopts

ERD ► Relationships have Characteristics  A relationship has Cardinality (Degree) One-to-OneOne-to-Many Many-to-Many

ERD ► Each entity’s participation is Mandatory or Optional ► Cardinality & Optionality are based on business rules Mandatory Optional

ERD ► One:One Relationship  One Member adopts one animal  One Animal is adopted by one member Member Animal Adopts

ERD ► One:Many relationship  One member adopts one animal  One animal is adopted by many members Member Animal Adopts

ERD ► Many:Many relationship  One member adopts many animals  One animal is adopted by many members Member Animal Adopts

ERD ► Optionality: Participation in a Relationship Zoo Employee Animal Cares for

ERD ► Mandatory  Every instance of the entity MUST participate in the relationship  Example: ► Every animal is cared for by at least one employee

ERD ► Optional  An instance of the entity CAN participate in the relationship  Example: ► Some employees do not take care of animals

ERD ► Drawing an E-R Diagram  Identify the entities  Write (make up) a few attributes for each entity  Designate the unique identifier (PK)  Identify the relationship (FK goes on the many side)  Show cardinality and optionality for each relationship

ERD ► E-R Modeling Exercise:  A Seminar Company ► A seminar company offers more than 100 different courses  Each course has a unique course number and a title ► The company schedules thousands of seminars annually  Each seminar is the presentation of one specific course  A seminar is either public or on-site

ERD ► E-R Model:  Entities ► Course  Course # (PK)  Course Title  Duration  Author

ERD ► E-R Model:  Entities ► Seminar  Seminar # (PK)  Date  Place  Type ► Public ► On-site  Course # (FK)

ERD ► E-R Model: COURSE SEMINAR Presented by

ERD ► E-R Modeling Exercise:  A Personnel Database ► A company has four divisions ► Each employee works for a department ► Each department reports to one of the divisions

ERD ► E-R Model:  Entities ► Division  Division #  Division Name

ERD ► E-R Model:  Entities ► Employee  Employee #  Employee Name  Dept # (FK)

ERD ► E-R Model:  Entities ► Department  Dept #  Dept Name  Div # (FK)

ERD ► E-R Model: DIVISIONDEPARTMENT Reports to EMPLOYEE Works for

Relational Database Theory ► E-R Modeling Exercise:  A Supplier-Parts Database ► A company purchases many parts from its suppliers  Each part has only one supplier ► A supplier can supply zero, one, or many parts  One _____(can/must) _____ (one and only one/one or more) ______

Relational Database Theory ► E-R Model: SUPPLIER PARTS Supplies

ERD Assignment 04 Page 117