Halsted’s Software Science-An analytical technique

1. Prepared By- Nur ISLAm Halsted’s Software Science- An Analytical Technique Department of Information Technology BESU, SHIBPUR 1

2. Halstead’s Software Science Halstead’s software science is an analytical estimation method . - Have scientific basis Starts with few simple assumptions about the product, Halstead used few primitive program parameters to develop expressions for: Overall program length Potential minimum volume and Program level Actual volume Effort Development time 2

3. Important Keywords Operator in general : a symbol or function representing a mathematical operation. assignments arithmetic and logical operators Parentheses pair, block begin/end pair If…then… else… endif Do…. While Statement terminator “;” Bitwise operator Pointers operator 3

4. Important Keywords Operands in general : A quantity to which an operator is applied – Subroutine declarations – Variable declarations – Variables and constants used with operators in an expression 4

5. Example 1. a=&b • Operands: a , b • Operators : = , & 2. func(a, b); • Operators: func, “,” , “;” , “()” • Operands: a , b 3. int func (int a, int b) { ... } • Operators: {} , (), “,” 5

6. Halstead’s Software Science • For any giving programs lets define the following parameters: – η1 be the number of unique parameters used in the program – η2 be the number of unique operands used in the program – N1 be the number of the total parameters used in the program – N2 be the number of the total operands used in the program 6

7. Halstead’s Software Science Length and Vocabulary : – Program Length (N)= N 1 + N 2 This notation agrees with our understanding of the total length of a program as the total count of tokens (operators and operands) – Program Vocabulary (η)= η 1 + η 2 7

8. Halstead’s Software Science Program Volume : Program volume (V) = is the minimum number of bits needed to encode the program – Program vocabulary and length depends on the programming style – Different lengths of programs, corresponding to the same problem when different languages are used – We need to express the program length by taking the programming language into consideration 8

9. Halstead’s Software Science Program volume (V) = is the minimum number of bits needed to encode the program – Program volume V = N log 2 ( η ) • To represent η different tokens we need log 2 (η) bits – Example: to represent 8 operands we need 3 bits • For a program of N length, we need N log2(η) bits – Program volume represents the size of the program by approximately compensating the effect of the programming language used 9

10. Halstead’s Software Science Potential Program Volume (V*) : – V* is the volume of the most concise program in which the problem can be coded – A program require at least 2 operators ( η 1=2) and the required number of operands is η 2 • Example : func() – Therefore: V* = (2+ η2) log2(2+ η2) – Program Level (L) = V*/V – Program level gives an indication of the language level of abstraction – Higher L , higher the language is easier to program with • Example: Assembly vs. C# 10

11. Halstead’s Software Science Effort and Time : – To obtain the needed effort , we divide the program volume (size) on the program level (complexity) –Effort = E =V / L = V /V* – The programmer’s time needed to finish the program (T) = E / S, where S is the speed of mental discriminations • The recommended value of S is 18 11 2

12. Halstead’s Software Science Estimation of Length : • Although the program length can be estimated easily using the previous discussed equation N = N1+N2, this can be done before starting the programming activities. • Instead, we can calculate the length depending on the unique numbers of operands and operators 12

13. Halstead’s Software Science • Halstead assumptions are based on: – Program are unlikely to have several identical parts that are greater than (η) – Identical parts are usually made into procedures and functions – Any program of length N consists of N/η unique strings (of length η) – for an alphabet of size K, there are K strings of length r r 13

14. Halstead’s Software Science N = η1 log2 (η1) + η2log2(n2) • Experimental evidence showed that the actual and the computed values are very close • Results may be inaccurate when dealing with small programs or subsystems individually 14

15. Recap 15 Unique operators : η 1 Unique Operands : η 2 Total Operators : N1 Total Operands : N2 Program Vocabulary : η = η 1+ η 2 Program Length : N=N1+N2 Program Volume : Nlog2 η Effort : E=V/L Time : T=E/S Estimated Length : N= η 1log2 η 1+ η 2log2 η 2 Estimated Effort : E=V.( η 1/ η 2).(N2/2)

16. Example Main() { int a, b, c, avg; scanf(“%d %d %d”, &a, &b, &c); avg = (a +b +c )/3; printf(“avg = %d”, avg); } 16

17. Example The unique operators are: main, (), {}, int, scanf, &, “, ”, “;”, =, +, /, printf The unique operands are: a, b, c, &a, &b, &c, a +b +c, avg, 3, “%d %d %d”, “avg = %d” therefore η1 = 12, η 2 = 11 N = 12 log2(12)+ 11log2(11) =81 V = Nlog2( η) = 81 log2(23) = 366 17

18. Resources • Wikipedia • Fundamentals of Software Engineering by Rajib Mall, Chapter 3 18

19. THANK YOU 19