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not. Our aim is to emphasize the fact that the source and target of an internal transition are
always the same and can only be a state (it can not be any other type of
StateVertex
).
The static semantics of the new proposed UML class diagram is defi ned by means of
OCL expressions. Basically they are the same rules proposed in OMG (2003), but with some
additional ones. We do not include them here because they do not represent any relevant
contribution.
Snapshot Layer
The dynamic (execution) semantics of State Machines is related to the Snapshot Layer
since this layer has to capture those aspects that are related to the status of a state machine
at a given moment. In order to specify the dynamic semantics, we take into account that the
actual behavior of a statechart “consists of a series of detailed snapshots ( ... ). The fi rst in
the sequence is the initial status, and each subsequent one is obtained from its predecessor
by executing a step” (Harel & Naamad, 1996). This excerpt is taken from the semantics
defi nition source of a particular CASE tool (
STATEMATE
, (Harel & Politi, 1998)), but it can
be considered as a widely accepted elemental description of statecharts behavior. On the
other hand, in the UML Specifi cation the dynamic semantics is described in English prose,
and in these natural language explanations several concepts have to be introduced, as for
example 'active state confi guration'.
In the same way that the base concepts are represented by means of a UML class dia-
gram, we propose to adopt an analogous approach with the snapshot concepts, by means of
the construction of another class diagram that we have called
Snapshot Diagram
(Figure 6). It
Figure 6: Snapshot Diagram
