On 5/25/07, Thilo Goetz <[EMAIL PROTECTED]> wrote:
I would like to revive the discussion that started with http://www.mail-archive.com/uima-dev@incubator.apache.org/msg01299.html
I still have the same concern about this that I posted to the previous thread: I think Michael is onto the same point that concerns me. To use this feature, components have to agree on what variable names they are going to use. So we're creating another kind of dependency that I believe should be documented in the capabilities. Sure, people could build this themselves already, but if we make it built-in then we're strongly encouraging its use and should consider all the implications. If we had more expressive capability spec (so you could say I create/require an instance of type FsVariable with name="Foo") then that might be a way to go. Thilo replied:
I guess we could do that in addition. How would you imagine this would work?
I'm mainly addressing a practical problem here, and want to give
people a viable
alternative to modifying the DocumentAnnotation. I think this
approach is fairly
forward-compatible as well, in the sense that it can later be
strengthened with
descriptor-based integrity constraints.
Actually I'm not happy about making the capabilities more complicated to handle this. I'm not sure the benefits of global variables outweigh either (a) making the capabilities more complicated or (b) adding/encouraging another set of implicit agreements between annotators that aren't declared anywhere. Let's go back and think about the DocumentAnnotation use case. Users can already declare their own document metadata type and add it to the indexes. Now that we have default bag indexes this is easy to do even if their document metadata type does not extend annotation. I think this is most of the way towards addressing the issue. What remains are (a) providing convenient access to a single indexed object, without going through an iterator, and (b) enforcing that there is only ever a singleton instance of a particular type. Another suggestion for addressing these issues: void CAS.indexSingleton(FeatureStructure aFS) throws CASException FeatureStructure CAS.getSingleton(Type aType) throws CASException The former is defined to throw an exception if the index over aFS.getType() is non-empty (for this view - we can have a separate "singleton" for each index repository - I think that is what we want for DocumentAnnotation), and otherwise to add aFS to the indexes. The latter is defined to throw an exception if there is not exactly one instance of aType in the indexes for this view, and otherwise to return the one instance. I like this better since it doesn't introduce yet another "name space" that annotators have to agree on amongst each other. -Adam
