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Hi all,

There has recently been some discussion about the possibility of
changing the semantics of component imports to be both more consistent
and easier to implement.

The current semantics are, to quote from the specification:

"


9.5.2 Treatment of imported components

* Imported components become named instances in the current model.
[ Imported components are treated as templates from which to
create instances in the current model. ]

"

What this means is that if you import the same component twice, you have
two separate copies / instances of the component in the model.

However, this creates an internal inconsistency with the next bullet
point under 9.5.2:
"

* For each |<cellml:import>| element in the current model, CellML
processing software must include each CellML component listed and
the connections between them.

"
because it is entirely unclear what connections are added when the same
component is imported twice in the same model element, or when
components with encapsulation relationships between them exist.

This problem can easily be repaired by changing import semantics to
being those of having one copy of the imported model, and then picking
components from that model to further expose to the importing model.
Components are not copied / used as templates, but instead are merely
allowed to be referenced in the importing model under a different name
(and the mathematics in them and the components encapsulated under them
become significant).

The following restriction is needed to ensure that this makes sense:
Definition: Components A and B are 'related by encapsulation' if A is
the same component as B, or if A is in the encapsulated set of B, or if
B is in the encapsulated set of A.

New entry under 9.4.1.2:
* An import element may not contain any pair of components which are
related by encapsulation.

Please send any comments you have about this proposed changed to
cellml-discussion at cellml.org.

Best regards,
Andrew Miller

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• [cellml-discussion] Changing component import semantics, Andrew Miller, 09/12/2007

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