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From Marshall Schor <...@schor.com>
Subject Re: [jira] [Commented] (UIMA-2409) CasCopier.copyCasView should be able to copy into a view with a different name
Date Tue, 18 Jun 2013 17:26:50 GMT
An edge case involving cross-view references:

Each AnnotationBaseFS (or subtype) holds a reference to the SofaFS it is an
annotation over.

Although these annotations may only be indexed in the view having the sofa they
are annotations over, it is possible that Instances of these may be referenced
in other views (cross-view linking).

When just one "view" is copied, these references end up referring to SofaFS
representing other views.  The current copier implementation is to get/create
these views in the target.  The sofas, if created, have no Sofa Data.   This is
one thing that could be changed: we could honor the boolean flag, aCopySofa, in
the API which controls whether or not the top level sofa for the view being
copied, has its data copied. 

When doing a view copy to another view with a different name, I think the
implementation needs to
  - check if the view associated in the source is the view being copied, and if so,
      - it should use the new target view.
  - if the view is not the same as the source being copied, then we could either
throw an exception, or silent/under-the-covers, create this additional view
(with the same name as in the source) in the target.  An ambiguity might occur
if the source's view name just happened to match the new target view name, I
suppose, but normally, this would result in additional views (other than the one
specified) being created as a side effect of copyCasView.  My suggestion is to
not throw an exception, but just to go ahead and create (or reuse) the
samed-named views in this case.  My rational is that this is an unlikely case in
the first place (it requires an advanced concept - cross-view linking), and so
accidental occurrences should be rare; it also has potentially some benefits -
allowing cas view copying in these cases, where it's probably unlikely the user
would even be referencing these cross-view links.   Also, for this case we have
the same issue of not setting in the destination CAS the sofa data that might be
present for these other views.

I plan to follow the current impl in *not* copying the sofa data for any new
views we might create via cross linking.  If a user wanted these, they can
always set the sofa data explicitly from the other CAS (a manual copy); but I
think it's unlikely they's  be wanted.

-----------
A similar special case exists for the DocumentAnnotation - there can be 0 or 1
of these per view in the CAS.  But other FSs (perhaps in other views) can hold
references to this FS (cross linking).  The same kind of view-switching (if the
source view is the view being copied, use the target view name instead) would be
used for this.

WDYT?

-Marshall


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