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DATABASE DESIGN USING THE REA DATA MODEL. Chapter 15. Designing and Implementing a Database System. Planning. Operation and maintenance. Requirements analysis. Implementation. Design. Coding. Data Modeling.

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designing and implementing a database system
Designing and Implementing a Database System

Planning

Operation and maintenance

Requirements analysis

Implementation

Design

Coding

data modeling
Data Modeling
  • Data modeling is the process of defining a database so that it faithfully represents all aspects of the organization, including its interactions with the external environment.
designing and implementing a database system4
Designing and Implementing a Database System

Planning

Operation and maintenance

Requirements analysis

Implementation

Data ModelingOccurs Here

Design

Coding

data modeling tools entity relationship diagrams
Data Modeling Tools: Entity-Relationship Diagrams
  • Entity-relationship (E-R) diagrams – graphical technique for portraying a database schema

Enrollment

Students

Line

Items

the rea data model
The REA Data Model
  • The REA data model is a conceptual modeling tool specifically designed to provide structure for designing AIS databases.
  • The REA data model provides structure in two ways:
  • By identifying what entities should be included in the AIS database
  • By prescribing how to structure relationships among the entities in the AIS database
the rea data model8
The REA Data Model
  • Three Basic Types of Entities
    • Resources that the organization acquires and uses.
    • Events in which the organization engages
    • Agents participating in these events
the rea data model an example
The REA Data Model: An Example

Salesperson

Inventory

Sales

Customer

Cashier

Cash

Accounts

Receive

Cash

the rea data model10
THE REA DATA MODEL
  • Structuring Relationships: The Basic REA Template
    • Rule 1: Each event is linked to at least one resource that it affects.
    • Rule 2: Each event is linked to at least one other event.
    • Rule 3: Each event is linked to at least two agents.
the basic rea template
The Basic REA Template

Agent A

Resource A

Event A

Agent B

Agent C

Resource B

Event B

the rea data model12
The REA Data Model
  • Rule 1: Every event entity must be linked to at least one resource entity
    • Some events affect the quantity of a resource:
      • “Get” events v. “Give” events
      • Stockflow relationships affect the quantity of a resource
      • Commitment event represent promises to engage in some future event
the rea data model13
The REA Data Model
  • Rule 2: Every event entity must be linked to at least one other event entity
    • Give and get events are linked together in an economic duality relationship
the rea data model a set of give get exchanges
The REA Data Model: A Set of Give &Get Exchanges

Get

Cash

Give

Inventory

Revenue Cycle

Give

Cash

Get

Inventory

Expenditure Cycle

Give

Cash

Get Employees’

Time

Human Resources/Payroll Cycle

Get

Cash

Give

Cash

Financing Cycle

Give (Use) Raw

Materials

Production Cycle

Give (Use) Employee Time

Get Finished Goods Inventory

Give (Use) Machinery & Equipment

the rea data model15
The REA Data Model
  • Rule 3: Every event entity must be linked to at least two participating agents
    • Accountability
    • Monitor the status of commitments and exchanges with outside parties
    • Links to at least two participating agents
developing an rea diagram
Developing an REA Diagram
  • STEP ONE: Identify the events about which management wants to collect information.
  • STEP TWO: Identify the resources affected by the events and the agents who participated.
  • STEP THREE: Determine the cardinalities between the relationships.
developing an rea diagram17
Developing an REA Diagram
  • Example: Typical activities in the revenue cycle include:
    • Take customer order
    • Fill customer order
    • Bill customer
    • Collect payment
developing an rea diagram18
Developing an REA Diagram

Take Order

Sale

Receive

Cash

developing an rea diagram19
Developing an REA Diagram
  • Step Two: Identifying the resources affected by the events and the agents who participated
  • Involves determining:
    • The resource(s) reduced by the give event.
    • The resource(s) increased by the get event.
    • The resources that are affected by a commitment event.
developing an rea diagram20
Developing an REA Diagram

Employee

Take Order

Inventory

Customer

Sale

Employee

Customer

Cash

Receive

Cash

developing an rea diagram21
Developing an REA Diagram
  • Step Three: Determining cardinalities between relationships
  • A cardinality describes the nature of the relationship between two entities.
    • It indicates how many instances of one entity can be linked to a specific instance of another entity
    • Cardinalities are often expressed as a pair of numbers.
    • The first number is the minimum, and the second number is the maximum.
developing an rea diagram22
Developing an REA Diagram
  • Minimum cardinality
    • Indicates whether a specific a instance of the entity next to the cardinality must be linked to at least one instance of the entity on the opposite side of that relationship
    • Can be either 0 or 1
developing an rea diagram23
Developing an REA Diagram
  • Maximum cardinality
    • Indicates whether one instance of that entity can be linked to more than one instance of the other entity participating in that relationship
    • Can be either 1 or N
developing an rea diagram24
Developing an REA Diagram
  • Using the crow’s feet notation:
    • The symbol for zero is a circle: O
    • The symbol for one is a single stroke: |
    • The symbol for many is the crow’s foot:
developing an rea diagram26
Developing an REA Diagram
  • Three Types of Relationships
    • Relationships depend on the maximum cardinality on each side of a relationship.
      • A one-to-one relationship (1:1) exists when the maximum cardinality for each entity in the relationship is 1.
      • A one-to-many (1:N) relationship exists when the maximum cardinality on one side is 1 and the maximum on the other side is many.
      • A many-to-many (M:N) relationship exists when the maximum on both sides is many.
developing an rea diagram34
Developing an REA Diagram

Employee

Take Order

Inventory

Customer

Sale

Employee

Customer

Cash

Receive

Cash

developing an rea diagram35
Developing an REA Diagram
  • Agent – event cardinalities:
    • The cardinality between agent and event is typically (0:N) on the agent side
  • Resource – event cardinalities:
    • The minimum cardinality is typically one
    • The maximum could be one or many
  • Event – resource cardinalities:
    • The minimum is typically zero
developing an rea diagram36
Developing an REA Diagram
  • Cardinalities between events
    • When events occur in a sequence, the minimum cardinality between the first event and the second event is always zero
    • The minimum cardinality between the second event and the first event is typically one
    • An exception could occur if the first event is not required for the second event to occur
    • The maximums in the cardinalities between events can be either one or many
developing an rea diagram37
Developing an REA Diagram
  • Uniqueness of REA Diagrams
    • Each organization will have its own unique REA diagram.
  • Data modeling is typically complex and repetitive
summary
Summary
  • We have:
    • Learned the steps to follow in designing and implementing a database system;
    • Learned how the REA data model is used to design an AIS database;
    • Learned how an entity-relationship diagram of an AIS database is drawn;
    • Learned how to read REA diagrams;
    • Learned what REA diagrams reveal about the activities and policies of the organization being modeled.