Condtion Tables

The ableC extensions adds so-called condition tables; these are useful in specifying complicated Boolean expressions. Condition tables are provided in requirements engineering languages such as RSML-e and SCR. They have been shown to be effecting in presenting complex specifications to domain-experts, such as pilots or air traffic controls in the avionics domain[1-3].

A simple example is shown in examples/simple.xc. An example of an altitude switch that uses condition tables can be found in examples/altitude_switch.xc.

Below is a sample condition table, from examples/simple.xc that references three Boolean values b1, b2, and b3.

    int c1 = table { b1 && b3 : T F
                     ! b2     : T *
                     b2 || b3 : F T };

This table is semantically equivalent to this less intuitive expression.

    int c2 = ((b1 && b3) && ((! b2) && (!(b2 || b3)))) || 
             ((!(b1 && b3)) && (1 && (b2 || b3)));

In the actual translation of these tables to plain C code, expressions in the table are not evaluated twice because they may contain side effects.

References

[1] Heninger, K.: Specifying software requirements for complex systems: New techniques and their application. IEEE Trans. on Software Engin. 6(1) (1980) 2–13.

[2] Leveson, N., Heimdahl, M., Hildreth, H., Reese, J.: Requirements Specification for Process-Control Systems. IEEE Trans. on Software Engin. 20(9) (1994) 684–706.

[3] Zimmerman, M.K., Lundqvist, K., Leveson, N.: Investigating the readability of state-based formal requirements specification languages. In: Proc. 24th Intl. Conf.on Software Engineering, ACM Press (2002) 33 – 43.