Lecture Notes in Computer Science 3472

18 Run-Time Verification 545
D t M is true if event e1 wastruebeforetimet andfromthattimeuptonowe2 has
not been ever true; and finally, definitions of negation, disjunction, conjunction
and implication are straightforward; note that ¬undefined is undefined.
Table 18.5.3 defines the semantics for conditions and events with respect to
model M at time t, the table is self-explanatory.
M , t |= c iff D t M (c) =true
M , t |= ek (ek prim.) iff ∃ state si such that τ(si) =t and LE (si, ek ) is defined
M , t |= ↑ c iff ∃ si.τ (si) =t ∧ M ,τ(si) |= c ∧ M ,τ(si−1) � c
i.e, ↑ c occurs when condition c changes from false to true.
M , t |= ↓ c iff ∃ si.τ (si) =t ∧ M ,τ(si) � c ∧ M ,τ(si−1) |= c
i.e, ↓ c occurs when condition c changes from true to false.
M , t |= e1 ∨ e2 iff M , t |= e1 or M , t |= e2
M , t |= e1 ∧ e2
iff M , t |= e1 and M , t |= e2
M , t |= e when c iff M , t |= e and M , t |= c
i.e, event e occurs when condition c is true.
Table 18.2. Semantics of events and conditions
Monitoring Script A PEDL script can monitor any object in the target system,
therefore declaration of monitored entities is performed in a language specific
manner. In the case of the Railway Gate example, a possible implementation
of the system is sketched in Figure 18.9; the PEDL script will monitor the variables
gateP osition and lightState and the methods open, close, on, off. For
simplicity, we assume that there is only one instance of GateController and
LightController classes.
class GateController{
public static final int UP = 0;
public static final int DOWN = 1;
public static final int UPDOWN = 2;
public static final int DOWNUP = 3;
int gatePosition;
public void open(){...}
public void close(){...}
...
};
class LightController{
public static final int OFF = 0;
public static final int FLASHING =
1;
int lightState;
public void on(){...}
public void off(){...}
...
};
Fig. 18.9. The implementation of the railway example
Primitive conditions are computed from boolean expressions over monitored
variables. An example of primitive condition is:
Cond is opening =(GateController.gateP osition == GateController.DOW NUP );