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Ch 15 - CONTROL AND AISs

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Ch 15 - CONTROL AND AISs Powered By Docstoc
					DATABASE DESIGN USING
 THE REA DATA MODEL

      Chapter 15
Designing and Implementing a
     Database System

                   Operation and
      Planning      maintenance




    Requirements
                   Implementation
      analysis




       Design         Coding
              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 System

                               Operation and
                  Planning      maintenance




                Requirements
                               Implementation
                  analysis
Data Modeling
Occurs Here



                   Design         Coding
   Data Modeling Tools: Entity-
     Relationship Diagrams
 Entity-relationship (E-R) diagrams – graphical technique
  for portraying a database schema




                            Line
   Enrollment              Items            Students
 Data Modeling Tools: Entity-
   Relationship Diagrams




Enrollment                                          Students


Entity Name   Attributes
Enrollment    Enrollment No., Enrollment Date, Enrollment Time
Student       Student ID No., Student Name, Student Address
       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:
1 By identifying what entities should be
  included in the AIS database
2 By prescribing how to structure relationships
  among the entities in the AIS database
       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



Inventory    Sales     Salesperson



                        Customer



  Cash      Receive
                         Cashier
Accounts     Cash
     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


Resource A   Event A    Agent A



                        Agent B



Resource B   Event B    Agent C
       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 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
     Give             Get
   Inventory         Cash          Revenue Cycle

     Give             Get
     Cash          Inventory       Expenditure Cycle


     Give        Get Employees’    Human Resources/
     Cash             Time         Payroll Cycle

     Give             Get
                                   Financing Cycle
     Cash            Cash

Give (Use) Raw
   Materials
  Give (Use)      Get Finished     Production Cycle
Employee Time    Goods Inventory
  Give (Use)
 Machinery &
 Equipment
        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
 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 Diagram

 Example: Typical activities in the revenue
  cycle include:
  – Take customer order
  – Fill customer order
  – Bill customer
  – Collect payment
Developing an REA Diagram

         Take Order




           Sale




          Receive
           Cash
  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 Diagram

            Take Order   Employee


Inventory
                         Customer

              Sale

                         Employee


             Receive
  Cash                   Customer
              Cash
    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 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 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 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 Diagram



 Sale              Customer
    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 Diagram

         Take Order




           Sale
Developing an REA Diagram



 Sale              Customer
Developing an REA Diagram




Inventory            Sale
Developing an REA Diagram

           Sale




           Cash
          Receipt
Developing an REA Diagram

           Sale




           Cash
          Receipt
Developing an REA Diagram

           Sale




           Cash
          Receipt
Developing an REA Diagram

           Sale




           Cash
          Receipt
   Developing an REA Diagram

            Take Order   Employee


Inventory
                         Customer

              Sale

                         Employee


             Receive
  Cash                   Customer
              Cash
   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 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 Diagram

 Uniqueness of REA Diagrams
  – Each organization will have its own unique
    REA diagram.
 Data modeling is typically complex and
  repetitive
                  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.

				
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posted:5/8/2010
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