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14 changes: 10 additions & 4 deletions chapters/annotations.tex
Original file line number Diff line number Diff line change
Expand Up @@ -1529,12 +1529,18 @@ \section{Graphical User Interface}\label{annotations-for-the-graphical-user-inte
\end{lstlisting}\end{synopsis}
\begin{semantics}
Allowed for simple types and components of a simple types.
If \lstinline!false!, then the variable defines a relative quantity, and if \lstinline!true! an absolute quantity.
If \lstinline!false!, then the component defines a relative quantity, and if \lstinline!true! an absolute quantity.
When converting between units (e.g., in plots and where parameters are edited), the unit offset must be ignored for relative quantities.
The annotation is inherited in the sense that when \lstinline!absoluteValue! is defined for a simple type, it also applies derived classes.
When \lstinline!absoluteValue! is defined for a simple type, it also applies to components declared with the type.

When \lstinline!absoluteValue! of a component is not determined by an annotation (possibly through inheritance), the \lstinline!absoluteValue! status may be inferred by the tool.
If the \lstinline!absoluteValue! of a component is neither determined by annotation nor inference, unit conversions that would differ depending on \lstinline!absoluteValue! cannot be performed.

\begin{nonnormative}
When converting between units (in the user-interface for plotting and entering parameters), the unit offset must be ignored for a variable defined with annotation \lstinline!absoluteValue = false!.
This annotation is used in the Modelica Standard Library, for example in \lstinline!Modelica.Units.SI! for the type definition \lstinline!TemperatureDifference!.
For most types there is no unit offset and the annotation is not needed for them.
For most quantities there are no units with offset, and the annotation is not needed.
For a component where unit conversions involving offsets could be of interest (mainly temperatures), ensuring that \lstinline!absoluteValue! is determined by an annotation (typically by means of using a type where it has been specified) may reduce impact of quality-of-implementation in tool ability to infer \lstinline!absoluteValue!.
Example applications of this annotation can be found among the type definitions in the \lstinline!Modelica.Units! package of the Modelica Standard Library, such as \lstinline!TemperatureDifference!.
\end{nonnormative}
\end{semantics}
\end{annotationdefinition}
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