D.3.3 ALGORITHMS FOR INCREMENTAL ... - SecureChange

8 F. Massacci and L.M.S. Tran
Example 3 (Controllable rule) In previous example, EM 1 has two possible design
alternatives as g 5 is either refined into {g 9 , g 12 }, or {g 9 , g 13 }. Let’s name these goal
sets EM 1,1 and EM 1,2 , respectively. Then, the controllable rule is as follows.
o
∗ ∗
r c1 =
nEM 1 −→ EM1,1 , EM 1 −→ EM1,2
Models incorporating evolution rules are called evolutionary models.
4 Specialization of the Approach on Goal-Based Model
In order to be concretely used by the stakeholders, the proposed approach for a
generic enterprise model with evolution rules needs to be instantiated to a concrete
syntax. Our choice is to use goal models. The first reason is obviously the expertise
that we could find at our own university. The second, possibly more important,
is that models for representing goals and objectives are well known in the ATM
domain (possibly under the name of “influence diagrams”).
In order to make our syntax concrete, some notions and concepts discussed
in generic sense are rephrased in the context of goal-based language. We further
discuss the visual presentation of evolution rules into goal models.
Basically, the general idea of goal-based approaches is the employment of goal
notion to study enterprise objectives or goals. Goals are refined (or decomposed)
into many subgoals in the sense that parent goal can be achieved if either all subgoals
are fulfilled (AND-decomposition). In this manner, goals are recursively decomposed
until operational goals (or tasks) that can be done by either software
systems or humans. Hence a goal-based enterprise model can be formally written
as follows.
Definition 4 (Goal-based enterprise model) A goal-based enterprise model is a
tuple 〈G, De〉 in which G is a set of goals, and De ⊂ G × 2 G is a set of ANDdecomposition
relations between goals.
Traditional goal models also include the notion of (OR-decomposition) where
the same goal can be fulfilled in different ways. We will not use in this setting ordecompositions
as they are better characterized by design alternatives in terms of
controllable rules (and better understood in this form by experts). A goal model itself
contains several design alternatives. Each design alternative is combination of
all different ways an arbitrary goal is decomposed. Since a goal is achieved when
all its refined goals is fulfilled, a final choice for the various design alternatives can
also be represented by the set of leaf goals required to fulfil all top goals.
The evolutionary goal model is intuitively a specification of the evolutionary
enterprise model aforemention, where the controllable rules are implicitly represented
by the different ways in which goals can be decomposed. The evolutiondependent
relations between observable rules are also implied based on the decomposition.
If rule r o1 , r o2 respectively apply to goal g 1 , g 2 , and g 2 is a (direct or
in direct) child of g 1 , then r o2 is evolution-dependent to r o1 . We additionally define