Internal Product Attributes
Internal product attributes describe the software products in a way that is dependent only on the product itself. The major reason for measuring internal product attributes is that, it will help monitor and control the products during development.
Measuring Internal Product Attributes
The main internal product attributes include size and structure. Size can be measured statically without having to execute them. The size of the product tells us about the effort needed to create it. Similarly, the structure of the product plays an important role in designing the maintenance of the product.
Measuring the Size
Software size can be described with three attributes −
Length − It is the physical size of the product.
Functionality − It describes the functions supplied by the product to the user.
Complexity − Complexity is of different types, such as.
Problem complexity − Measures the complexity of the underlying problem.
Algorithmic complexity − Measures the complexity of the algorithm implemented to solve the problem
Structural complexity − Measures the structure of the software used to implement the algorithm.
Cognitive complexity − Measures the effort required to understand the software.
The measurement of these three attributes can be described as follows −
Length
There are three development products whose size measurement is useful for predicting the effort needed for prediction. They are specification, design, and code.
Specification and design
These documents usually combine text, graph, and special mathematical diagrams and symbols. Specification measurement can be used to predict the length of the design, which in turn is a predictor of code length.
The diagrams in the documents have uniform syntax such as labelled digraphs, data-flow diagrams or Z schemas. Since specification and design documents consist of texts and diagrams, its length can be measured in terms of a pair of numbers representing the text length and the diagram length.
For these measurements, the atomic objects are to be defined for different types of diagrams and symbols.
The atomic objects for data flow diagrams are processes, external entities, data stores, and data flows. The atomic entities for algebraic specifications are sorts, functions, operations, and axioms. The atomic entities for Z schemas are the various lines appearing in the specification.
Code
Code can be produced in different ways such as procedural language, object orientation, and visual programming. The most commonly used traditional measure of source code program length is the Lines of code (LOC).
The total length,
LOC = NCLOC + CLOC
i.e.,
LOC = Non-commented LOC + Commented LOC
Apart from the line of code, other alternatives such as the size and complexity suggested by Maurice Halsted can also be used for measuring the length.
Halstead’s software science attempted to capture different attributes of a program. He proposed three internal program attributes such as length, vocabulary, and volume that reflect different views of size.
He began by defining a program P as a collection of tokens, classified by operators or operands. The basic metrics for these tokens were,
μ1 = Number of unique operators
μ2 = Number of unique operands
N1 = Total Occurrences of operators
N2 = Number of unique operators
The length P can be defined as
$$N = N_{1}+ N_{2}$$
The vocabulary of P is
$$\mu =\mu _{1}+\mu _{2}$$
The volume of program = No. of mental comparisons needed to write a program of length N, is
$$V = N\times {log_{2}} \mu$$
The program level of a program P of volume V is,
$$L = \frac{V^\ast}{V}$$
Where, $V^\ast$ is the potential volume, i.e., the volume of the minimal size implementation of P
The inverse of level is the difficulty −
$$D = 1\diagup L$$
According to Halstead theory, we can calculate an estimate L as
$${L}' = 1\diagup D = \frac{2}{\mu_{1}} \times \frac{\mu_{2}}{N_{2}}$$
Similarly, the estimated program length is, $\mu_{1}\times log_{2}\mu_{1}+\mu_{2}\times log_{2}\mu_{2}$
The effort required to generate P is given by,
$$E = V\diagup L = \frac{\mu_{1}N_{2}Nlog_{2}\mu}{2\mu_{2}}$$
Where the unit of measurement E is elementary mental discriminations needed to understand P
The other alternatives for measuring the length are −
Object-oriented development suggests new ways to measure length. Pfleeger et al. found that a count of objects and methods led to more accurate productivity estimates than those using lines of code.
Functionality
The amount of functionality inherent in a product gives the measure of product size. There are so many different methods to measure the functionality of software products. We will discuss one such method ─ the Albrecht’s Function Point method ─ in the next chapter.
