SEKE 2012 Proceedings - Knowledge Systems Institute

Since most of the existing approaches merge all of the
identical states, they result in overgeneralized FSMs. In [7],
some criteria are propos ed to identify identical states that
have emergent behavior. This definition is as follows:
Definition 5: The component i in MSC m has emergent
behavior in state , if there exists MSC n (m and n can be
equal) and a state
, such that and are identical
states and one of the following holds:
i) = where l is a c omponent
and represents message with content c sent
from i to l.
ii) = where lis a co mponent
and represents a message with content c
received by i from l. Component l sends a message
with content c to component i such that i
does not receive this message before event of
in MSC m and by removing this event, still
component l can send .
iii) State is the final state of MSC n and
is a send message for component i.
iv) Case ii) h olds except th at by removing event of
in MSC m, component l cannot send
anymore. Then, there exist events e and w for l
such that the event of is syntactical cause for
. Then, states and are identical
and emergent behavior occurs for l.
Only the identical states that result in emergent
behaviors based on Definition 5 s hould be merged and
unnecessary merging for the other states should be avoided.
Behavior Model algorithm (Figure 7), is prop osed to
synthesize behavior models while preventing emergent
behaviors due to overgeneralization.
Algorithm: Behavior Model
Input: Set of message sequence charts (M)
Output: State machines for each component
1. For each component i:
2. Make domain theory D i based on Definition 2.
3. Make state machines and assign state values based on Definition 3.
4. Find identical states based on Definition 4.
5. For each set of identical states:
a. If they lead to emergent behavior based on Definition 5:
Merge the states to one single state.
b. Otherwise, no merging is needed.
Figure 7. Synthesis of emergent behavior preventing
overgeneralization
To show the effectiveness of Definition 5 and the
proposed algorithm, the case study is considered. MSC m1
has emergent behavior since case i) of Definition 5 holds for
it. For th e FSMs of client control in MSC m2 (shown in
Figure 6) the proposed algorithm is applied and the identical
states are f ound to be , and . However, these
states do not lead to e mergent behavior since they do not
hold any of four cases in Definition 5. The reason is that in
cases ii) and i v) of Definition 5, the event that comes after
the identical states should be a receive message while in this
example, the event is a send message. In cases i) and iii) ,
although the event that comes after identical states is
sending message which matches the example, one of the
identical states should be th e final state i n the machine or
the next event should be different for the identical states in
order to produce emergent behavior. Since none of these is
valid for the example, the identical states of MSC m2 do not
lead to emergent behavior and merging them is unnecessary.
V. CONCLUSIONS AND FUTURE WORK
It has been reported that detecting unwanted behavior
during the design phase is 20 times cheaper th an finding
them during the deployment phase [11]. This paper provides
a systematic approach to anal yze system requirements for
defects, while saving on overhead by replacing ad-hoc
methodologies with automated ones. A new algorithm is
developed for behavior model synthesis and emergent
behavior detection while preventing overgeneralization. The
proposed algorithm improves the existing ad-hoc methods
[7, 13]. The future work is implementing the proposed
algorithm as a syntax checker to provide an automated tool
to check and correct the system designs. Moreover this work
can be u tilized as part o f a comprehensive framework to
analyze system requirements and design.
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