Halstead theory - Total number of distinct operator & operand occurrences measures

Discussion

• Nirja Shah   -Posted on 23 Oct 15
  - Researchers generally agree that simple size measures like lines of code (LOC) are not adequate for determining software complexity and development effort.
  
  - They are of the view that, for this purpose, a programming process model is needed.
  
  - This model is based upon manageable number of factors, that affect the complexity and quality of the software systems.
  
  - A number of researchers including Halstead, McCabe have attempted to define such programming models.
  
  - Halstead’s model also known as theory of software science is based on the hypothesis that program construction involves a process of mental manipulation of the unique operators (n₁) and unique operands (n₂).
  
  - It means that a program of N₁ operators and N₂ operands is constructed by selecting among n₁ unique operators and n₂ unique operands.
  
  - By using this model, Halstead derived a number of equations related to programming such as program level, the implementation effort, language level and so on.
  
  - Also, it is one of the most widely studied theories and has been supported by a number of empirical studies.
  
  - An important and interesting characteristic of this model is that a program can be analyzed for various features like size, effort etc. by simply counting its basic parameters n₁, n₂, N₁ and N₂.
  
  - Program vocabulary is defined as
  
  N = n₁ + n₂
  
  - And program actual length as
  
  N = N₁ + N₂
  
  - One of the hypotheses of this theory is that the length of a well - structured program is a function of n₁ and n₂ only. This relationship is known as length prediction equation and is defined as
  
  N_h= n₁log₂n₁ + n₂log₂n₂
  
  - This length equation estimates the size of the program from the counts of unique operators (n₁) and unique operands (n₂).
  
  - If the actual length (N) agrees well with the estimated value (N_h), then the program is considered as well structured.

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