STRL STRL
© STRL 1996-2011







2 Semantics

The informal semantics of the most interesting constructs are as follows:

  • C A  : if interval is non-empty then the value of A  in the next state of that interval else an arbitrary value.
  • fin A  : if interval is finite then the value of A  in the last state of that interval else an arbitrary value.
  • skip  unit interval (length 1).
  • f1 ; f2   holds if the interval can be decomposed (“chopped”) into a prefix and suffix interval, such that f1   holds over the prefix and f2   over the suffix, or if the interval is infinite and f1   holds for that interval.
  •  *
f holds if the interval is decomposable into a finite number of intervals such that for each of them f  holds, or the interval is infinite and can be decomposed into an infinite number of finite intervals for which f  holds.

Let [[ ...]]e  be the “meaning” (semantic) function from Expressions   × (Σ+ ∪ Σ ω)  to V al  and let [[...]]  be the “meaning” function from F ormulae  × (Σ+ ∪ Σ ω)  to Bool  (set of Boolean values, {tt,ff} ) and let σ =  σ0σ1...  be an interval. We write        ′
σ ~v σ if the intervals σ  and  ′
σ are identical with the possible exception of their mappings for the variable v  . The formal semantics is listed in Table 2:


Table 2: Semantics of ITL
|------------------------------------------------------------------|
|[[ z ]]eσ                =    ˆz                                       |
|[[ a ]]eσ                =    σ0(a) and for all 0 < i ≤ |σ |,σi(a) = σ0(a )
|[[ A ]]eσ               =    σ0(A)                                   |
|[[ g(e1,...,en) ]]e     =    ˆg([[ e1 ]]e ,...,[[ en]]e)                    |
|             σ            { σ  σ(A )       σ         if |σ | > 0      |
|[[ C A ]]eσ              =        1                                   |
|                          { choose-any-from (V al)   otherwise      |
|[[ fin A ]]eσ             =      σ |σ|(A )                if σ is finite    |
|                            choose-any-from (V al)   otherwise      |
|[[ true ]]σ            =    tt                                      |
|[[ q]]σ                =    σ0(q) and for all 0 < i ≤ |σ |,σi(q) = σ0(q)
|[[ Q ]]σ               =    σ0(Q)                                   |
|[[ h(e ,...,e ) ]] = tt iff  ˆh([[ e ]]e,...,[[ e ]]e)                      |
|    1      n σ                1 σ      n σ                        |
|[[ ¬f ]]σ = tt          iff   not ([[ f ]]σ = tt)                         |
|[[ f1 ∧ f2 ]]σ = tt     iff   ([[f1 ]]σ = tt) and ([[ f2]]σ = tt)           |
|[[ skip ]]σ = tt         iff   |σ | = 1                                 |
|[[ ∀v o f]]= tt       iff   (for all σ′ s.t. σ ~v σ′,[[f ]]σ′ = tt)     |
|[[ f1 ;f2 ]]σ = tt      iff                                           |
|  (exists k, s.t. [[ f1 ]]σ0...σk = tt and [[ f2]]σk...σ = tt)                |
|   or (σ is infinite and [[ f ]] = tt)       |σ|                       |
|  *                     1 σ                                       |
|[[ f ]] = tt           iff                                           |
|if σ is finite then                                                 |
|  (exist l0,...,ln s.t. l0 = 0 and ln = |σ| and                      |
|    for all 0 ≤ i < n,li ≤ li+1 and [[ f ]]σli...σli+1 = tt)               |
| else                                                              |
|  (exist l ,...,l s.t. l = 0 and                                    |
|         0     n     0                                            |
|   [[ f ]]σln...|σ| = tt and                                            |
|    for all 0 ≤ i < n,li ≤ li+1 and [[ f]]σli...σli+1 = tt)               |
|   or                                                             |
|  (exist an infinite number of li s.t. l0 = 0 and                    |
|    for all 0 ≤ i,li ≤ li+1 and [[ f]]σl...σl = tt)                     |
|                                i   i+1                            |
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November 14, 2011
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