Information Technology Reference
In-Depth Information
Informally, the definition of
ended sla
specifies that if the event
E
2 involves
an act
A
that causes user
U
's status to be downgraded and the conditions ex-
pressed on
U
's assignment to
L
as a consequence of
E
2 happening are satisfied
then
U
's assignment to
L
is ended by
E
2.
Definition 11.
An
act
U
(
E
1
,A
)
clause is a clause of the form
act
U
(
E
1
,A
)
←
act
(
E
1
,a
i
)
where
a
i
∈A
is an upgrading action.
Definition 12.
An
act
D
(
E
2
,A
)
clause is a clause of the form
act
D
(
E
2
,A
)
←
act
(
E
2
,a
j
)
where
a
j
∈A
is an downgrading action.
There will be an
act
U
(
E
1
,A
) rule and an
act
D
(
E
2
,A
) rule for each up-
grading act and each downgrading act
a
∈A
. The sets of upgrading acts and
downgrading acts are disjoint.
The condition part of the
ECL
I
and
ECL
T
rules in the definitions of
started sla
and
ended sla
respectively define the application-specific conditions
on the performance of an action of status level assignment and deassignment.
These conditions must be true in order for the action to be performed of assign-
ing (deassigning) a requester agent
u ∈U
. The
upgrade conditions are expressed by a set of rules with the head
ECL
I
(
E,U,L
)
that define the conditions on the initiation of an agent
U
to a status level
L
as a consequence of the occurrence of an event
E
in which
U
performs an up-
grade action. The downgrade conditions are expressed by rules with the head
ECL
T
(
E,U,L
) that define the conditions on the termination of the assignment
of an agent
U
to a status level
L
as a consequence of the occurrence of an event
E
in which
U
performs a downgrading action.
The conditions of the
ECL
I
to (from) a status level
l
∈L
and
ECL
T
rules split into
database predicates
and
evaluable predicates
.
Definition 13.
The database predicates are predicates that are defined by a set
of clauses
that include no built-in operators of a logic programming language,
and are such that no clause in
D
D
violates the local stratification condition.
Definition 14.
The evaluable predicates are predicates that are expressed in
terms of the set of comparison operators in
{
=
,
=
,<,
≤
,>,
≥}
or the mathemat-
ical operators in
{
+
,
−
,
×
,
÷
, mod
}
.
Definition 15.
ECL
I
and
ECL
T
are defined by clauses of the forms:
ECL
I
(
E
1
,U,L
)
←
DB, EV.
ECL
T
(
E
1
,U,L
)
←
DB, EV.
