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Specification of Reactive Hardware/Software Systems - Electronic ...

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278 Process Part <strong>of</strong> POOSL<br />

envs2, Sysp and Sys) in a single transition step by performing atomic action a. 3 This<br />

transition step is either performed completely or not at all. If an extended behaviour<br />

specification can choose between alternative transition steps, it always leaves all alternatives<br />

open until one <strong>of</strong> them can actually be performed. Hence, a choice to perform<br />

a particular transition step is never made a priori. In general, the environment <strong>of</strong> an<br />

extended behaviour specification will only permit a limited number <strong>of</strong> transition steps.<br />

If more transitions are open at the same time, a choice is made non-deterministically.<br />

An extended behaviour specification cannot perform any transition steps different from<br />

those specified by £<br />

£ ¡ a<br />

¡ Act¦ a .<br />

The labeled relations are defined by 9 axioms (1’) ¡ ¡ (9’) and 24 rules (a’) ¡ ¡ (x’) in<br />

Section A.2. In this subsection we will only select a number <strong>of</strong> them and explain each <strong>of</strong><br />

these in more detail.<br />

(1’) Internal computation<br />

<br />

C S § p <br />

¡£ Er¢ ¥ ¡ ¡<br />

¥ ps¥ ¥ Sys E1£ ¡ ¡ p <br />

<br />

£ Sys¡ ¥<br />

if<br />

§ C p E1£ ¡ ¡ ¡£ Er¢ ¥<br />

<br />

¤ ¥ ¡ ¡ ¥ ps¡ ¥<br />

¡<br />

¡ ¡ ¥ ps¡ ¥<br />

¡ ¥ Sys ¡<br />

¡<br />

¥ Sys ¡ p ¥ Sys<br />

( ¡<br />

¥ ps¥ ¥ Sys ) ¡ S¥<br />

Axiom (1’) deals with the execution <strong>of</strong> a data statement S within process C p (E1 ¥¡ ¡ ¡ ¥ Er).<br />

The semantics <strong>of</strong> this execution is calculated by applying semantic function (see<br />

Subsection 8.5.4) to configuration ¡<br />

¥ Sys S¥ ¡ ¥ ps¥ . The function application yields a<br />

collection <strong>of</strong> terminal configurations. Each <strong>of</strong> these configurations reflects a possible<br />

effect <strong>of</strong> the execution <strong>of</strong> S. For configuration <br />

¡<br />

¥ ps¡ ¥ ¡ ¥ Sys ¤ ¥ ¡ ¡<br />

¡ ps¡ ¡<br />

, this effect is reflected by<br />

state , process stack and type ¡<br />

¤ ¡ (so data object is not required). The execution <strong>of</strong> S<br />

is not observable by the environment <strong>of</strong> C p (E1 ¥¡ ¡ ¡ ¥ Er). Extended behaviour specification<br />

C p (E1 ¥¡ ¡ ¡ ¥ Er) terminates successfully (the statement that remains to be executed by<br />

C p (E1 ¥¡ ¡ ¡ ¥ Er) is ).<br />

<br />

§ S C p E1£ ¡ ¡ ¡ £ Er¢ therefore performs a silent ( ¡ ) action. If this action is performed, the process<br />

(2’) Message send<br />

<br />

¥¡ ¡ ¡ ¥ En) ch!m(E1 § Cp E¢1 £ ¡ ¡ ¡£ <br />

¡ ¡<br />

¥ ps¥ ¥ Sys E¢r¢ ¥<br />

p <br />

<br />

Sys ¥<br />

if<br />

§ C p E ¢1 £ ¡ ¡ ¡£ E ¢r¢ ¥<br />

¡<br />

data¤<br />

¤ £<br />

ch!m£<br />

¡ ps¡ ¡ ¡ ¥ ¥ ¥ Sysp ¥ Sys<br />

<br />

Sys ¡<br />

¤ ¡ ¡<br />

¥ ¥ ¥ ¥ 1 1 ps1 1 ( ¡ ¡<br />

¥ ¥ Sys ¥ ps¥<br />

<br />

¡<br />

¥ Sys ¡<br />

¤ ¡ ¥ ¥ ¥<br />

E1 ) ,<br />

2 2 ps2 2 ( ¡ ¡ ¥ 1¥ ¥<br />

¡ 1¥ Sys ¡<br />

<br />

¡<br />

¥ ps¡ ¥ ¡ ¥ Sys ¡ ¡ ¤ ¡ ¥<br />

E2 ps1 ) , ,<br />

n ( Sys<br />

¡<br />

¥ ¥ ¡ ¥ ¥<br />

¡ <br />

<br />

¡ ¤ ¥ ¥ ¤ ¥ ¡ ¡ ¡<br />

¡ ¥ ¡ <br />

En n 1 psn 1 n 1 ) and<br />

1 n are Sys-structures<br />

¡ ¥ ¥¡ ¡ ¡<br />

<br />

¥ ¡ ¡ ¤ ¡ ¥ ¡ )¥¡ ¡ ¡ ¥ where data copy( 1 copy( ¡<br />

¡ ¥ ¡ ¥ ¤ n<br />

¡ )<br />

3 Sometimes we will ascribe the ability to perform transition steps or atomic actions to configurations<br />

in stead <strong>of</strong> to their extended behaviour specifications.

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