1. Information Systems Development MIS331
Logical and Logic
Modeling
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MIS331

2. Agenda System Modeling Logical versus Physical
Process Modeling with Data Flow Diagrams
Logic Modeling
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MIS331

3. Process Modeling
Graphic representation of functions or processes which capture, manipulate, store, and distribute data.
System boundary is defined by where the data enters and exits the system
Takes advantage of the concept of functional decomposition
Process models can be constructed in a layered fashion such that increasing levels of complexity can be illustrated
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MIS331

4. Data Flow Diagram (DFD)
Identifier
Process
Name
Gane & Sarson
Nomenclature
Process
Data Store
File
Name
Entity
Name
Source/Sink
Data Flow
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MIS331

5. Process versus Entity
How do we decide if something is a process or an entity?
If this “something” alters data as a function of the system then it is a process.
creates a report, sorts, calculates, reads or writes, etc.
If this “something” simply generates data as input to the system or accepts data as output from the system then it is an entity.
customer submits an order
customer receives item ordered
Processes are inside the system boundary, entities are outside
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MIS331

6. Coding the Process Identifier
Context level
defines the entire system and its external entities
Level 0
defines the primary individual processes
identifier is X.0 where X equals the process number
Level 1
first decomposition of Level 0 processes into sub-processes
identifier is X.Y.0 where Y equals sub-process number
Level n
the result of n nested decompositions
identifier is X.Y n.0
Functional Primitive Level
lowest logical level where no further decomposition yields benefits
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MIS331

7. Simple System Decomposition
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8. All data flows must begin and/or
The Rules of DFDs
In a nutshell…
All data flows must begin and/or
end at a process, because data
flows either initiate or result from a
process.
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MIS331

9. Three Basic Illegal Data Flows
Entity
Name
Identifier
Process
Black Hole
Identifier
Process
Name
File
Miracle
1.0
Create
Paychecks
Employee
File
Gray Hole
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MIS331

10. Logic Modeling
Logic Modeling is logical but it is not Logical Modeling
Logical Modeling is the representation of processes and their relationships to other processes.
Logic Modeling is the representation of the internal structure and functionality of processes and subprocesses.
How are inputs converted to output?
When does a process occur?
When should a process not occur?
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MIS331

11. Logic Modeling Tools Structured English Decision tables and trees
just a modified version of good ol’ English
Decision tables and trees
models of conditions and actions as tables or graphs
State-transition diagrams and tables
shows the various states a system component can assume
events that result in a transition from one state to another
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MIS331

12. Structured English Take the hours_wrkd and multiply them by
Relies on strong, imperative verbs and noun phrases
read, write, sort, move, add, begin, end, etc.
uses only nouns and terms previously defined in the data dictionary
Undefined adjectives or adverbs are not used unless clearly defined in the data dictionary as value ranges for data element descriptions
avoids the construction of compound sentences
Take the hours_wrkd and multiply them by
the pay_rate and then put this value into the
field called gross_pay.
Calculate gross_pay using the formula:
hours_wrkd * pay_rate.
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MIS331

13. Decision Tables
Better than Structured English when logic becomes nested and complex
If Employee=“S” then pay base salary else,
If Employee=“H” then calculate wage and
If hours_wrkd < 40 then produce absence report else,
If hours_wrkd are > 40 then calculate overtime.
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MIS331

14. Decision Tree
Depicts the decision scenarios as a connected series of nodes and branches which ultimately end in one or more actions
probabilistic and nonprobabilistic
probabilistic trees allow for condition probabilities to be carried throughout the decision process
Nodes are decision points
Branches are alternative paths
Actions are the expected result of a decision based on the variables or constraints in place
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MIS331

15. Decision Tree If Employee=“S” then pay base salary else,
If Employee=“H” then calculate wage and
If hours_wrkd < 40 then produce absence report else,
If hours_wrkd are > 40 then calculate overtime.
Salaried?
Pay base salary 1
Pay hourly wage
Absence report
< 40
= 40 2
Pay hourly wage
Hourly?
> 40
Pay hourly wage
Pay overtime wage
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MIS331

16. When to Use What
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MIS331

17. For Next Time More on DFDs on Thursday
Get a good grip on this material
It may show up on a knowledge demonstration
Case #1 Presentation on Tuesday
Get prepared for Group A’s presentation
Know Case #1 inside and out.
Start thinking about KD #1
It will be here before you know it…
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