bis 360 – lecture six (part 2) conceptual data modeling (chapter 10 and partial chapter 12)
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BIS 360 – Lecture Six (Part 2)
Conceptual Data Modeling
(Chapter 10 and partial Chapter 12)
1. Determine system requirements (ch. 7)
2. Structure system requirements (ch. 8-10) 3. Generate alternative for selection (ch. 11)
SDLCWhere are we?
Project ID and Selection
Project Initiation & Planning
Analysis
Logical Design
Physical Design
Implementation
Maintenance
Data ModelingProcessing ModelingLogic Modeling
Differences between Modeling
• Data Modeling - Using Entity-Relationship Diagram (ER diagram or ERD)– identify What (types of data) needed in the system
• Process Modeling - Using Data Flow Diagram (DFD)– identify Where and How (which pieces of data) to be used
• Logic Modeling - Using Structured English, Decision Table, and Decision Tree– detail System Logic and Functional Structure
ERD and DFD
Data Model(ER Diagram)
Data Modeling(ER Diagramming)
Process Modeling(Data Flow Diagramming)
Process Model(Data Flow Diagram)
(more static)
(more dynamic)
Some Basic Jargons
Model: An abstract representation of “reality”
Data Model: An organization of data to represent the “reality.”
Data Modeling: a technique used to create a “Data Model.”
Conceptual Data Modeling: a technique to capture both “data” and its “meaning” required by an organization
Conceptual Data Modeling
It is:• presenting what data are needed in the system• independent from “how” data are stored• Independent from which DBMS to be used
Its deliverables:• A preliminary ER model
(address only Entities and Relationships)
• A refined ER diagram (with detailed attributes for each entity)
An Example-- A Preliminary Entity-Relationship Model
An Example-- A Refined Entity-Relationship Diagram
ERD - basic concepts
Entity A thing (tangible/intangible) that can be uniquely identified -- indicated by a noun, it could be a(n):– Person– Object (e.g., machine, tool, equipment, document)– Concept (e.g., position, movie, etc.)
Symbol:a symbol for an
Entity
ERD - basic concepts
Relationship:• An association between one or more
entities -- described by a verb phrase; it is bi-directional
Symbol:A Line
(with Crow’s foot)
• Entity Type - the object set that shares a common group of characteristics, e.g., STUDENT (SID, Name, Phone, Major)
• Entity instance - an occurrence of an Entity Type, e.g., (1234, Mike Taylor, 387-5428, CIS)
ERD - basic concepts Entity Type vs. Entity Instance
ERD - Extended Concepts
Associative Entity: a special relationship that contains its characteristics to associate instances of one or more entity types.
Symbol:
EMPLOYEE COURSEcompletes
Date
Weak Entity: an “entity” depends on another entity for its existence.
Symbol:
Weak Entity
EMPLOYEE SPOUSE
ERD - Extended Concepts
How to Characterize a Relationship?
Cardinality:The number of occurrences (instances) involved at each side of a relationship– zero or One– one and only one– zero or many– one or many
(Optional one)
(Mandatory one)
(Optional Many)
(Mandatory Many)
Relationship: Extended Concepts
Degree of a Relationship: The number of entity types involved in a relationship.
• Unary - a R within an entity itself
• Binary - a R between two different entity types
• Ternary - a R exists among three entity types
1 to 1(1:1)
1 to many(1:M)
many to many(M:N)
Binary Relationships
Employee Spouse
is a spouse of
hasVehicle Type Modelis of
registers
Course
is registered by
Student
is married to
Unary Relationships
Person
is a spouse of
is married to
1 to 1
manages
1 to MEmployee
is managed by
consists of
M to NPart
is a component of
Unary Relationships(a complete graph)
Person
is a spouse of
is married to
1 to 1
consists of
M to NPart
is a component of is managed by
1 to MEmployee
manages
Unary Relationships
• Each Employee may manage one or more Employees.
• Each Employee must be managed by one and only one Employee.
manages
is manages by
1 to MEmployee
More Unary Relationship!
Course
has a prerequisite
is a prerequisite of
Q. What is the cardinality for the above unary relationship?
More Unary Relationship!(A complete graph)
Course
has a prerequisite
is a prerequisite of
Why? Can you explain the above diagram?
Ternary Relationship
A relationship that simultaneously involves 3 entities!
How to Characterize an Entity?
AttributeA characteristic (property) of an entity or a
relationship– Key (identifier)– Candidate key– Non-key attribute
Examples:EMP (EmpID, Name, Address, DOB)DEPT (DeptID, DeptName, DeptAddress)
Foreign Key
Foreign key: It is an attribute ( or a set of attributes) that is used as a Primary Key in some other entity.
EMP DEPT
EMP (EmpID, Name, Address, DOB)
DEPT (DeptID, DeptName, DeptAddress)
How to Resolve a M:N Relationship?
It is quite common to encounter a M:N relationship - which needs to be represented as an “Associative entity”.
Most DBMS can not represent a M:N relationship, we need to ...
Use the two PKs as the PK andFKs in the associative entity
Sup_PART
SUPPLIER PARTSID PID
An Example for an M:N Relationship Associative Entity
SUPPLIER(SID, Name, SSN, Phone, Addr)
PART (PID, Description)
SUPPLIERSID
Name SSN PhoneAddr
PART
PID Descrip
Associative Entity Price
Sup_PARTSup_PART
(SID, PID, Price)
How to Conduct the ER Diagramming?
Step 1 - Identify all interested Entities
Step 2 - Identify proper relationships between entities
Step 3 - identify the Key and non-key attributes for each entity
Step 4 - Verify the validity of the final ER diagram
Validation of ERDRules:
• The entity name must be a noun
• The entity name must be unique
• The entity must have an identification or primary key
• Each relationship is described by a verb (phrase)
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