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CMSC 132:
Object-Oriented Programming II
Problem Specification & Design
Department of Computer Science
University of Maryland, College Park
Overview
Problem specification
Obstacles
Program design
How to divide w ork
Interface & conditions
Problem Specification
Goal
Create complete, accurate, and unambiguous
statement of problem to be solved
Problems
Description may not be accurate
Description may change over time
Difficult to spec ify behavior for all input s
Natural langua ge description is imprecise
Formal specifica tion languages limited an d difficult
to understand
Problem Specification
Example
Specification of input & output for progra m
Problem Specification Problems
Description may not be accurate
Problem not understood by customer
Description may change over time
Customer changes their mind
Difficult to specify behavior for all inputs
Usually only covers common cases
Hard to conside r all inputs (may be imp ossible)
Example
Most UNIX utilit ies crash with random input s
Problem Specification Problems
Description may be ambiguous
Natural langua ge description is imprecise
Why lawyers use legalese for contracts
Formal specification languages are limited and
may be difficult to understand
Examples
Find sum of all values in N-element list L
between 1 and 100
∑
L
i
∋(L
i
≥1) ∧(L
i
≤100)
Difficult to write specifications that are both
readable and precise
i = 0
N-1
