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Figure 2: Statecharts diagrams for thermostat furnace relay
illustrative examples in Harel and Naamad (1996) have been depicted using a shaded box
symbol to represent active states, and the Rhapsody tool by I-Logix uses a thicker line to
represent enabled transitions during the animation of statechart models. We have made use
of a similar approach for the specifi cation of the diagrams (2, 3, 4) of Figure 2. It is necessary
to note that we are not stating that this kind of notation must be used by the analyst during
modeling, but, in order to specify in detail the behavior of statecharts, a clear distinction
has to be made between the basic view and the snapshot view notions. It seems clear that
the support of graphical examples and specifi cations can be of great help in order to clarify
this subtle distinction.
The other fundamental elements of the architecture are the maps traced from the
Base Layer to the Snapshot Layer (map
TTT
) and from the Snapshot Layer to itself (map
T
). On the one hand, map
T
). On the one hand, map
T TTT
starts from the information available at the Base Layer, and
determines one status that is fi xed as the representation of the initial status of the system.
In the case of the thermostat example we have mentioned, map
TTT
will specify the passage
from Diagram 1 to Diagram 2 as an initial status. In particular, the setting-up of the state
'Furnace OFF' as the initial active state (since, on sight of the model in Diagram 1, this is
the default situation) must be embedded in map
TTT
. On the other hand, map
T
, starting from
T
a current status, determines the next status the system will reach. In fact, map
T
refl ects the
T
behavior of the system, enabling the representation of an execution trace of this behavior
by means of consecutive applications of the map. With regard to the thermostat, map
T
will specify the passage from a current status (Diagram 2) to the next status (Diagram 4)
(as we show in the next subsection, Diagram 3 represents an intermediate situation). For
instance, map
T
embodies the dynamic principle stating that if 'Furnace OFF' state is active
T
and 'desired-temp' is higher than 'room-temp' then 'Furnace ON' state must become active
(and of course 'Furnace OFF' inactive). Up to this point, the explanation of the maps of the
architecture lies in the Model Level of the Metamodeling Architecture. At the Metamodel
Level, maps
TTT
and
T
formalize respectively the processes of 'fi xing the initial status' and
T
'moving from the current status to another', which are common to every model at the Model
Level. These processes will be different according to the modeling language being described.
For example, as will be shown in the chapter, in the specifi c case of UML State Machines,
map
T
specifi es the
run-to-completion step.
Refi nement of the Architecture
The proposed architecture can be refi ned, adapting to our perspective the dimension
of
granularity
as stated for instance in Rolland, Souveyet and Moreno (1995), where it is
proposed that “a single process modeling formalism should accommodate a wide range of
model granularity in a homogeneous fashion”. In general, the highest levels of complexity
