Algorithms II
Software Development
Life-Cycle
CMSC104
Section 301 Fall 2005
Problem Solving
• Problem solving is the
process of transforming the
description of a problem into
the solution of that problem by
using our knowledge of the
problem domain and by
relying on our ability to select
and use appropriate problemsolving strategies, techniques,
and tools.
Why Use Computers
• Use a computer to solve a problem if:
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It has extensive input.
It has extensive output.
Its method of solution is too complicated
to implement manually.
If done manually, it takes an excessively
long time to solve.
We expect to use the same method
often.
Software Development Life Cycle
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Requirements Specification
Analysis
Design
Implementation
Testing and Verification
Documentation
Maintenance and
Enhancement
Requirements Specification
Analysis
Design
Implementation
Testing and Verification
Documentation
Maintenance and
Enhancement
The Problem - QuikTax
The phone rings one day and we
get an offer from QuikTax, a
local federal income tax
preparation service to
“Develop a computer program
to compute income tax from
tax schedules for the tax year
2006.”
Requirements Specifications
• One of the most important steps in
problem solving is understanding
exactly
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•
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•
what the problem is,
what is needed to solve it,
what the solution should provide,
and if there are constraints and special
conditions.
• In this step you eliminate
ambiguities in the problem
statement.
Analysis
• In this phase we identify:
– Inputs to the problem and their form
– Outputs expected from the solution and their
form
– Special Constraints
– Assumptions
– Formulas
Inputs
• What items must be provided to be able to
get a solution?
– Taxable income
$0.00 to $1,000,000,000.00
– Filing status
Single, Married/Jointly, Married/Separate,
Head of household
– Number of dependents
0 - 99
Output
• Intermediate results
• Final results
– Completed tax information
Constraints
• What are the limits on the data?
– Income can not be a negative
number.
– Number of dependents must be
zero or positive, but not more
than what number ?
– Filing status must be one of a
set of values
Assumptions
Problem deals in $US
 Only for 2006
 What’s implied by the Requirements?

Formulas
• For income tax, it is the tax tables.
• For determining the area, it is
length x width
• For grades, it is:
>90.0%
A
80.0% - 89.99%
B
70.0% - 79.99%
C
60.0% - 69.99%
D
>60.0%
F
Design
• Develop a series of steps with a logical order
which, when applied to the input would produce
the specified output. (does this sound like an
ALGORITHM?)
• This phase is when you think about how to solve
the problem!!
• This phase can take
40% of the effort.
Implementation
• Implementation is the phase where the design is
transformed into code.
• This is the only portion of the process that is
computer and compiler specific.
• This should be approximately 10% of the effort.
Implementation Errors
• Design errors
• Syntax errors
• Run-time errors
Testing and Verification
• Once the code is developed:
– Prove the program produces correct results.
– Prove that the program that was built solves the problem
that was described in the requirements specification.
• Manually solve the problem with a data set, then compare that
to the program’s output!
Documentation
• Consists of
– A concise requirements specification
– Description of inputs, outputs, constraints, and
formulas used
– Pseudocode or flowchart of the algorithm
– Source code listing
– Hard copy of a sample of data and the output
– User’s guide explaining how to use the program
Maintenance and Enhancement
• Environments change, so
programs must be changed
– Tax tables change
– Name of organization changes
• Users want (or need) the
program to do more
– New tax credits
– Elimination of old tax credits.