FOSD Program Cubes
A program in Feature Oriented Software Development (FOSD) is a composition of features: a base program is augmented with increments in program functionality, called features, to produce a complex program. A software product line (SPL) is a family of related programs. A typical product line has F0 as a base program, and F1..Fn as features that could be added to F0. Different compositions of features yield different programs. Let + denote the feature composition operation. A program P in SPL might have the following expression:
That is, P extends program F0 with features F1, F2, F4, and F8 in this order.
We can recast P in terms of a projection and contraction of a 1-dimensional array. Let Fi = [F0 .. Fn] denote the array of features used by a product line. A projection of Fi eliminates unneeded features, yielding a shorter array (call it) Gi. A contraction of Gi sums each Gi in a specific order, to yield a scalar expression. The expression for P becomes:
where the index values accomplish projection and summation is array contraction. This idea generalizes to n-dimensional arrays that model multi-dimensional product lines.
A multi-dimensional product line is described by multiple interacting sets of features. As an elementary 2D example, it is easy to create a product line of calculators, where variants offer different sets of operations. Another variation might offer different presentation front ends to calculators, one with no GUI, another with a Java GUI, a third with a web GUI. These variations interact: each GUI representation references a specific calculator operation, so each GUI feature cannot be designed independently of its calculator feature. Such a design leads to a matrix: columns represent increments in calculator functionality, and rows represent different presentation front-ends. Such a matrix M is shown to the right: columns allow one to pair basic calculator functionality (base) with optional logarithmic/exponentiation (lx) and trigonometric (td) features. Rows allow one to pair core functionality with no front-end (core), with optional GUI (gui) and web-based (web) front-ends.
An element Mij implements the interaction of column feature i and row feature j. For example, the element labeled cb is a base program that implements the core functionality of a calculator. Element gb adds code that displays the core functionality as a GUI; element wb adds code that displays the core functionality via the web. Similarly, element ct adds trigonometric code to the core calculator functionality; elements gt and wt add code to display the trigonometric functionality as a GUI and web front-ends.
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