Chapter 7 Process Modeling

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Chapter 7Process Modeling
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Agenda

• Process modeling mechanics
• Some rules for building DFDs
• Decomposing DFDs
• Using DFDs for better analysis
• Examples

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Learning Objectives

• After this chapter, you should be able to
• Read and interpret process models (DFDs)
• Construct DFDs using specific rules and
  guidelines presented in the chapter
• Decompose DFDs into lower-level diagrams
• Balance higher- and lower-level DFDs
• Explain differences among 4 types of DFDs
• Use data flow diagrams as a tool to support the
  analysis process
• Explain and diagram use cases to model system

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Processing Modeling

• Part of Requirements Structuring within the
  Analysis Phase of the SDLC
• A common form of process modeling is the data
  flow diagram (DFD)
• DFD is a picture of the movement between external
  entities and the processes and data stores within
  a system.

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Deliverables for Process Modeling

• Context diagram
• DFDs of current physical system (as needed)
• DFDs of current logical system
• DFDs of new logical system
• Descriptions of each DFD component

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DFD Definitions

• Data Store
• Process
• Source/sink
• Data flowThink about How are these concepts
  related to general principles of systems
  thinking from Appendix 1?

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Example

• Fast Food Restaurant Think of Events and
  Describe
• Sources/Sinks
• What data are provided by what external
  components
• What data are received by what external
  components
• Processes
• What components transform data
• What are those transformations
• Data Flows
• For a specific interrelationship of components,
  what specific data (attributes of entities) flow
• What is the interface that facilitates that flow
• Data stores
• What are some data stores, i.e., components that
  hold data
• For one, what specific data (attributes of
  entities) are stored

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Symbols
Source/Sink
Process
Data flow
Data store
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Diagrams

• Context Overview of an organizational system
  that shows boundaries, external entities, and
  major information flows
• See Figure 7-4 (p. 203)
• Level-0 Represents a systems major processes,
  data flows, and data stores at a high level of
  detail
• See Figure 7-5 (p. 204)

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SomeBut Not AllBasic DFD Rules (Know Table 7-2
and Figure 7-6!)

• Inputs of a process are different than the
  outputsthe process makes some change to the
  data, or else it must not be needed!
• Objects on a DFD have unique names
• Processes must have both inputs and outputs,
  otherwise they are a source or a sink
• Process verbit DOES something
• Data cant go directly from a store to another
  storemust be moved via process
• Data store noun
• Data cant go directly from a source to a
  sinkmust move via process

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Rules, Rules, and More Rules (cont.)

• Data flows in one direction at a time (no
  two-headed arrows)
• Data flow cant go directly back to the same
  process it leavesmust go via at least one other
  process (otherwise, why did it have to leave in
  the first place?)
• Data flow to a data store means update (delete or
  change)
• Data flow from a data store means retrieve or use
• Data flow has a noun phrase label (type of data
  moving)

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Decomposition

• What is functional decomposition?
• Why is it important?
• How does this apply to DFDs?

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More Decomposition

• When the system is broken down to its lowest
  level, this is known as the primitive level
• Level n-diagram Is a DFD that is generated from
  n nested decompositions from a level-0 diagram

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Balancing DFDs

• Conservation of inputs and outputs when the
  process is decomposed to a lower level
• DFDs must have the same inputs and outputs when
  decomposingdecomposing simply adds detail
  internal to the system
• Compare Figure 7-4 and 7-5 (pp. 203-204)
• Compare Figure 7-5 and 7-8 (pp. 204, 209)

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DFD Types

• Current Physical
• Current Logical
• New Logical
• New Physical

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Guidelines for DFD

• Complete
• Consistent
• Timing issues
• Iterative nature
• Primitive DFD
• How to know when youre there?

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Developing DFDs
Develop context and Level-0 DFDs for the Open
Road Insurance system The purpose of the Open
Road Insurance system is to provide automotive
insurance to car owners. Initially, customers
are required to fill out an insurance application
request. A drivers record request is sent to
the local police department, which sends back a
drivers record report. Also, a vehicle
registration request is sent to the Department of
Motor Vehicles, which supplies a vehicle
registration. Policy contracts are sent in by
various insurance companies. The agent
determines the best policy for the type and level
of coverage desired and gives the customer a copy
of the insurance policy along with an insurance
coverage card. The customer information is now
stored. Periodically, a fee statement is
generated, which along with addendums to the
policy is sent to the customer, who responds by
sending in a payment with the fee stub.
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Developing DFDs
Develop context and Level-0 DFDs for a dentist
office system Is description complete? Whenever
new patients are seen for the first time, they
complete a patient information form that asks for
their name, address, phone number, and brief
medical history, which are stored in the patient
information file. When a patient calls to
schedule a new appointment or change an existing
appointment, the receptionist checks the
appointment file for an available time. Once a
good time is found for the patient, the
appointment is scheduled. If the patient is a new
patient, an incomplete entry is made in the
patient file the full information will be
collected when the patient arrives for the
appointment. Because appointments are often made
so far in advance, the receptionist usually mails
a reminder postcard to each patient 2 weeks
before his or her appointment.
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Developing DFDs
Develop context and Level-0 DFDs for a real
estate system Is description complete is
Level-0 primitive? A Real Estate Inc. (AREI)
sells houses. People who want to sell their
houses sign a contract with AREI and provide
information on their house. This information is
kept in a database by AREI and a subset of this
information is sent to the citywide
multiple-listing service used by all real estate
agents. AREI works with two types of potential
buyers. Some buyers have an interest in one
specific house. In this case, AREI prints
information from its database, which the real
estate agent uses to help show the house to the
buyer (a process beyond the scope of the system
to be modeled). Other buyers seek AREIs adivce
in finding a house that meets their needs. In
this case, the buyer completes a buyer
information form that is entered into a buyer
database, and the AREI real estate agents use its
information to search AREIs database and the
multiple-listing service for houses that meet
their needs. The results of these searches are
printed and used to help the real estate agent
show houses to the buyer.
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Summary

• What is a DFD?
• Why use a DFD?
• What is a context diagram?
• What are different levels of DFDs?
• What are balanced DFDs?
• What are different types of DFDs?
• Learn the rules for constructing DFDs.

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Context Diagram (Figure 7-4)
Return
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Level 0 Diagram (Figure 7-5)
Return