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Up until 20/12/2002, an ordinary agent u m has the status l 1 if u m maintains
an account balance at least 1000 Euros. Conversely, up until 20/12/2002, if
u m makes a withdrawal that takes u m 's balance below 1000 Euros then the
downgrading act of withdrawal results in a status level transition from l 1 to l 2 .
After 20/12/2002, an ordinary agent u m must maintain a balance of at least
1100 Euros for u m to have the status l 1 . Moreover, if u m is an ordinary user
then u m has the status l 2 whenever u m deposits a sum that terminates a period
of time during which u m 's account was overdrawn and u m was assigned to l 3 ;
u m 's assignment to l 2 is terminated/ u m 's assignment to l 3 is initiated when u m 's
account becomes overdrawn. If u m is a Gold-card holder then a different policy
applies, to wit: Gold-card holders have status l 1 as long as they do not overdraw
by more than 100 Euros. If a Gold-card holder makes a withdrawal that results in
his or her account being overdrawn by more than 100 Euros then the withdrawal
induces a state transition from l 1 to l 2 . The policy relating to Gold-card holders
is not subject to any temporal constraint.
Suppose that the bank's policy is that, in the interval [01 / 12 / 2002 ,
31 / 12 / 2002], users with an l 2 status level may read any object other than o 2 ,
and that agents with a status level l 1 can write object o 1 up until 24/02/2002.
For that, the following pla clauses are included in SBAC ( ψ ):
pla ( read, O, l 2 )
current time ( T ) , 01 / 12 / 2002
T,T
31 / 12 / 2002 ,O
= o 2 .
pla ( write, o 1 ,l 1 )
current time ( T ) ,T < 24 / 02 / 2002 .
To represent the conditions on status level initiation and termination, an
APA would include the following ECL I
and ECL T
clauses in SBAC ( ψ ):
ECL I ( E,U,l 1 )
current time ( T ) , object ( E,O ) , ordinary ( U ) ,
balance ( O, X ) ,X
1000 ,T
20 / 12 / 2002 .
ECL T ( E,U,l 1 )
current time ( T ) , object ( E,O ) , ordinary ( U ) ,
balance ( O, X ) ,X < 1000 ,T
20 / 12 / 2002 .
ECL I ( E,U,l 1 )
current time ( T ) , object ( E,O ) , ordinary ( U ) ,
balance ( O, X ) ,X
1100 ,T > 20 / 12 / 2002 .
ECL T ( E,U,l 1 )
current time ( T ) , object ( E,O ) , ordinary ( U ) ,
balance ( O, X ) ,X < 1100 ,T > 20 / 12 / 2002 .
ECL I ( E,U,l 1 )
object ( E,O ) , goldcard ( U ) , balance ( O, X ) ,X
≥−
100 .
ECL T ( E,U,l 1 )
object ( E,O ) , goldcard ( U ) , balance ( O, X ) ,X <
100 .
ECL I ( E,U,l 2 )
object ( E,O ) , ordinary ( U ) , balance ( O, X ) ,X
0 .
ECL T ( E,U,l 2 ) ← object ( E,O ) , ordinary ( U ) , balance ( O, X ) ,X < 0 .
ECL I ( E,U,l 3 )
user ( E,U ) .
ECL T ( E,U,l 3 )
user ( E,U ) .
 
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