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[cellml-discussion] A list of proposed changes to semantics to makein CellML 1.2


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  • From: jonathan.cooper at comlab.ox.ac.uk (Jonathan Cooper)
  • Subject: [cellml-discussion] A list of proposed changes to semantics to makein CellML 1.2
  • Date: Fri, 21 Dec 2007 14:20:23 +0000
On Thu, Dec 20, 2007 at 12:30:32AM +0800, David Nickerson wrote:
> > * The current specification says:
> > "A variable with either a private_interface or public_interface
> > attribute
> > value of "in" must be mapped to no more than one other variable in the
> > model. [ Note that a similar restriction does not apply to variables
> > with
> > interface values of "out". An output variable can be mapped to multiple
> > input variables in various components in the current model. ]"
> >
> > The problem with this is that it doesn't properly account for
> > mappings where a variable is forwarded into an encapsulated block. As
> > an example, consider the following encapsulation hierarchy (higher
> > components encapsulate lower ones)...
> >
> > A
> > |
> > B
> > / \
> > C D
> >
> > Suppose that component A has, for variable v,
> > public_interface="none", private_interface="out", and B has for
> > variable v, public_interface="in", private_interface="out"
> > (connected to A), and C and D have public_interface="in",
> > private_interface="none", both of which are connected to B.
> >
> > There is no reason why this should not be valid. However, the
> > specification contradicts itself on whether this is allowed. On one
> > hand, because B has private_interface="out", it "can be mapped to
> > multiple input variables in various components in the current
> > model.", but because it has a public interface of in, it "must be
> > mapped to no more than one other variable in the model".
> >
> > This can be fixed by firstly defining the interpretation of
> > connections and interfaces, and then adding constraints based on
> > that which actually describe which connections are allowed to each
> > set of variables.
>
> will be interesting to see how such a definition ties in with the idea
> of input variables becoming output variables based on the way the
> components are hooked together :)

Indeed.

The use of "in" and "out" on interfaces very strongly implies that
connections have a directionality, and this is also reflected in the
quote from the specification above - it assumes that variables are only
defined in one place, and hence it doesn't make sense to import a
variable (via an "in" interface) from multiple locations. It does
however make sense to export a variable to multiple locations, or forward
an imported variable to multiple locations (the example Andrew gives).

If we don't want connections to have directionality, then I think this
requires quite a major change in the specification, even if only to avoid
user confusion. For example, I would want to deprecate the use of "in"
and "out", and instead allow public_interface="yes" or
public_interface="no" (perhaps a synonym for "none") and similarly for
private interfaces. The terms used in the language then reflect the
nature of the interfaces - if connections are bidirectional, then it
doesn't make sense to talk of an "in" interface, since it may function
either as input or output depending on the other components in the
system.

Jonathan.

--
Jonathan Cooper MSN: msn at jonc.me.uk www: jonc.me.uk/

We are tribbles of Borg. Prepare to be replicated.


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