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Software Measurement

Halstead’s Software Science

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Maurice Halstead

Originally a meteorologist– Involved in first cloud seeding

In 1970’s he did empirical studies looking for relationships between code and the “ilities” – maintainability, readability, testability, etc

Wanted to find the intrinsic things to measure

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Vs Physics

Study blue metal balls vs white tennis balls.Conclude that blue balls made bigger dents than white balls.

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Halstead's software science

every token is either an operator or an operand

tokens with a value are operands 2 is the number of unique operands

other tokens are operators 1 is the number of unique operators

is the total number of unique tokens = 1 + 2

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Sample Program

Z = 0; while X > 0

Z = Z + Y ;

X = X - 1 ;

end-while ; print (Z) ;

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Counts

= 3 ; 5 while-endwhile 1 > 1 + 1 - 1 print 1 () 1

Z 4 0 2 X 3 Y 1 1 1

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Counting Rules

Halstead also was concerned about algorithms and not about declarations, i/o statements, etc.

Thus, he did not count declarations, input or output statements, or comments.

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Counting Rules

There is a lot of debate about counting rules. In fact there was a conference that dealt just with counting rules. One conclusion, the results are not very sensitive to the counting rules. Pick a set of rules and be consistent.

Suggest syntax-oriented counting rules

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Counting Rules

if two symbols always occur together, count them as one operator.

if there are two different structures that are semantically the same, still count them as two different operators.

count declarations, i/o, etc. Count everything that is necessary for expressing the program.

operators are basically keywords. user-defined items are basically operands.

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Length, N

N = N1 + N2

where, N1 is the total number of operators and N2 is the total number of operands

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estimate of the length, est N

If N and est N are not within 30% of each other, it is not reasonable to apply any of the other software science measures.

estN 1 1 2 2log log

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TTYP1 - Calculate Halstead’s

cin >> a >> b >> c;if (a > b){ cout << “hello”;

if (c < a){cout << “part 1”;if ( c > b){cout << “part 2”;

}}

else{ cout << “part 3”;}}else{if (c<a){cout<<”part 4”;}

}cout << “exiting”;