Transcript DFD: Data Flow Diagram

Software Engineering in CS at APU
CS 470 Software Engineering I
Sheldon X. Liang
Ph. D.
November 2, 2015 Azusa, CA
Azusa Pacific University, Azusa, CA 91702, Tel: (800) 825-5278
Department of Computer Science, http://www.apu.edu/clas/computerscience/
November 2, 2015
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Software Engineering in CS at APU
CS 470 Classical Analysis
Azusa Pacific University, Azusa, CA 91702, Tel: (800) 825-5278
Department of Computer Science, http://www.apu.edu/clas/computerscience/
November 2, 2015
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Software Engineering in CS at APU
CS 470 Classical Analysis
Systems Analysis:
1. What to do: the evaluation of an activity to
identify its desired objectives and determine
procedures for efficiently attaining them.
2. What needed: the methodical study of the
data-processing needs of a business or
department, together with
recommendations for specific hardware
and software installations.
Azusa Pacific University, Azusa, CA 91702, Tel: (800) 825-5278
Department of Computer Science, http://www.apu.edu/clas/computerscience/
November 2, 2015
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Software Engineering in CS at APU
CS 470 Classical Analysis
Role of the Analyst
• The analyst is the liaison between the
user and the development team.
• His final product must be understandable
to the users and the developers.
• He doesn’t tell the developers how to
create the product, just what it should do
in a very exacting manner.
Azusa Pacific University, Azusa, CA 91702, Tel: (800) 825-5278
Department of Computer Science, http://www.apu.edu/clas/computerscience/
November 2, 2015
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Software Engineering in CS at APU
CS 470 Classical Analysis
Azusa Pacific University, Azusa, CA 91702, Tel: (800) 825-5278
Department of Computer Science, http://www.apu.edu/clas/computerscience/
November 2, 2015
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Software Engineering in CS at APU
CS 470 Classical Analysis
The Goal of Analysis
• The most important product of systems analysis – is
the specification document.” - DeMarco
– Informal enough for the client
• The client is generally not a computer specialist
– Formal enough for the developers
• It is the sole source of information for drawing
up the design
Azusa Pacific University, Azusa, CA 91702, Tel: (800) 825-5278
Department of Computer Science, http://www.apu.edu/clas/computerscience/
November 2, 2015
6
Software Engineering in CS at APU
CS 470 Classical Analysis
Specification Document
• The specification document is the final product of
the systems analyst
• It is a contract between the client and the
developer
• Specifies what the product must do and the
constraints on the product
Azusa Pacific University, Azusa, CA 91702, Tel: (800) 825-5278
Department of Computer Science, http://www.apu.edu/clas/computerscience/
November 2, 2015
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Software Engineering in CS at APU
CS 470 Classical Analysis
Methods of Analysis
• Demarco(1979) – Data Flow Diagram
– Data Dictionary
– Structured English
– Decision Tables
– Decision Trees
Azusa Pacific University, Azusa, CA 91702, Tel: (800) 825-5278
Department of Computer Science, http://www.apu.edu/clas/computerscience/
November 2, 2015
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Software Engineering in CS at APU
CS 470 Classical Analysis
Structured Systems Analysis
• The analysts job:
– What business functions should she
computerize?
• Accounts payable
• Accounts receivable
• Inventory
– What equipment will they need?
– How much are they willing to spend?
Azusa Pacific University, Azusa, CA 91702, Tel: (800) 825-5278
Department of Computer Science, http://www.apu.edu/clas/computerscience/
November 2, 2015
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Software Engineering in CS at APU
CS 470 Classical Analysis
Step 1. Draw the DFD
• The data flow diagram (DFD) shows the logical data flow
– “What happens, not how it happens”
• First refinement
– Infinite number of possible interpretations
Azusa Pacific University, Azusa, CA 91702, Tel: (800) 825-5278
Department of Computer Science, http://www.apu.edu/clas/computerscience/
November 2, 2015
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Software Engineering in CS at APU
CS 470 Classical Analysis
Step 1. Draw the DFD
• Second refinement
– PENDING ORDERS is scanned daily
Azusa Pacific University, Azusa, CA 91702, Tel: (800) 825-5278
Department of Computer Science, http://www.apu.edu/clas/computerscience/
November 2, 2015
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Software Engineering in CS at APU
CS 470 Classical Analysis
Step 1. Draw the DFD
• Portion of third refinement
Azusa Pacific University, Azusa, CA 91702, Tel: (800) 825-5278
Department of Computer Science, http://www.apu.edu/clas/computerscience/
November 2, 2015
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Software Engineering in CS at APU
CS 470 Classical Analysis
Step 2. Decide What Parts to Computerize and How
• It depends on how much client is prepared to
spend
• Large volumes, tight controls
– Batch
• Small volumes, in-house microcomputer
– Online
• Cost/benefit analysis
Azusa Pacific University, Azusa, CA 91702, Tel: (800) 825-5278
Department of Computer Science, http://www.apu.edu/clas/computerscience/
November 2, 2015
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Software Engineering in CS at APU
CS 470 Classical Analysis
Step 3. Determine the Details of the Data Flows
• Determine the data items for each data flow
• Refine each flow stepwise
• We need a data dictionary for larger products
Azusa Pacific University, Azusa, CA 91702, Tel: (800) 825-5278
Department of Computer Science, http://www.apu.edu/clas/computerscience/
November 2, 2015
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Software Engineering in CS at APU
CS 470 Classical Analysis
Structured Systems Analysis
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Response times cannot be determined
The number of I/O channels can only be guessed
CPU size and timing can only be guessed
Nevertheless, no other method provides these data for
arbitrary products
Overall
• The method of Gane and Sarsen/De Marco/ Yourdon has
resulted in major improvements in the software industry
Azusa Pacific University, Azusa, CA 91702, Tel: (800) 825-5278
Department of Computer Science, http://www.apu.edu/clas/computerscience/
November 2, 2015
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Software Engineering in CS at APU
CS 470 Classical Analysis
Take a look at my research
Azusa Pacific University, Azusa, CA 91702, Tel: (800) 825-5278
Department of Computer Science, http://www.apu.edu/clas/computerscience/
November 2, 2015
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Software Engineering in CS at APU
CS 470 Classical Analysis
Thank you very much!
Questions?
Azusa Pacific University, Azusa, CA 91702, Tel: (800) 825-5278
Department of Computer Science, http://www.apu.edu/clas/computerscience/
November 2, 2015
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