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7.5. Static Semantics for Models
7.5.7. Undefinable Static Semantics
A constraint type for the data flow graph types that is probably meaningful was not yet specified.
It concerns to not used input and output ports of any data type in gMainFunctionBlock and
gSubFunctionBlock graphs. It seems meaningful to require that any available port of objects
in those graph types should be used or rather connected. The behaviour is that in cases, in
which inputs are not set, the corresponding output(s) cannot be directly defined. It can be
an initial value but also the last value set in ETCS Mode or Application Level, in which the
output was used last.
The reason why a general OCL constraint cannot be defined for this purpose is that in
MERL only ports that are in a connection are accessible. Unconnected ports are simply not
visible to any generator. Therefore, unconnected ports cannot be found in the GOPPRR C++
abstract syntax model, which is used for the constraint checking.
The only currently possible work-around for this situation is to define an own constraint for
each concrete object type with ports while using the knowledge about its port number in the
constraint.
For example, for the oAND type, which has two Boolean inputs and one Boolean output,
the following statement is defined to require that all its input ports must be used,
1 context CProject
2 inv : m_GraphSet−>s e l e c t (m_Type = ’ gMainFunctionBlock ’ or m_Type =
’ gSubFunctionBlock ’ )−>f o r A l l (
3 f u n c t i o n |
4 f u n c t i o n . m_ObjectSet−>s e l e c t (m_Type = ’oAND ’ )−>f o r A l l (
5 o b j e c t |
6 f u n c t i o n . m_BindingSet . m_Connection . m_Calls−>s e l e c t ( m_pObject = o b j e c t and m_pRole
= ’ DataInput ’ ) . m_pPort−>s i z e ( ) = 2
7 )
8 )
Listing 7.30: oAND input port constraint
The requirement that all output ports are connected is not that crucial because those unconnected
ports cannot cause an undefined calculation result, but it might be useful to avoid unused
objects in graphs. The corresponding constraint for the oAND type is defined as follows.
1 context CProject
2 inv : m_GraphSet−>s e l e c t (m_Type = ’ gMainFunctionBlock ’ or m_Type =
’ gSubFunctionBlock ’ )−>f o r A l l (
3 f u n c t i o n |
4 f u n c t i o n . m_ObjectSet−>s e l e c t (m_Type = ’oAND ’ )−>f o r A l l (
5 o b j e c t |
6 f u n c t i o n . m_BindingSet . m_Connection . m_Calls−>s e l e c t ( m_pObject = o b j e c t and m_pRole
= ’ DataOutput ’ ) . m_pPort−>a s S e t ( )−>s i z e ( ) = 1
7 )
8 )
Listing 7.31: oAND output port constraint
The main difference to the input port constraint is that output ports can be connected more
than once. Therefore, a multiple times connected port may only be counted once. This is done
by the OCL asSet() [63, p. 158] statement. Because those constraints only differ in the object
type name and the number of input and output ports, those are not presented here for other
object types.
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