| [higgins-dev] IdAS: Model as Metadata |
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Thinking out loud here -- I mentioned this on the last dev call.
I believe IdAS consumers need the ability to make updates to aspects of a context's model (i.e. add a new subject type, or add a new attribute type).
So to do that, we would naturally start introducing a bunch of add* methods to the model interfaces like we did for context and its sub-elements. This starts feeling like a duplication of similar methods, so I started wondering if there's a simpler way.
What if we decided to remove the interfaces in org.eclipse.higgins.idas.api.model, and instead define some metadata types that can be used to represent model elements? If we could make this work, I would prefer it for a few reasons:
1) It reduces the number of interfaces we have,
2) I think the model of an element is a good example of metadata (it truly is data that describes the data),
3) It makes us start using metadata -- helping to prove out the design.
The problems I see with doing it:
P1) Metadata is too simple: Today, metadata is always single-valued and a simple type. So if we wanted an IContext to have metadata for the digital subject models it supports, we would have to basically have one huge string value. This makes updates very unfriendly. We would want to allow metadata to be multi-valued such that we could have a metadata element with a type of "http://...#DigitalSubjectModel" and multiple values where each value represents a supported digital subject model. Furthermore, it would be good if each digital subject model were complex such that a specific sub-element could be updated (i.e. so one could add to the list of attributes valid for that subject). I know... we just got done making metadata simple and single-valued, and now I'm proposing to change it back.
P2) Lack of functional methods in metadata: like IAttributeSimpleValueModel::toLexicalForm(Object). I'm not sure if this is a real problem or if these methods were just for convenience.
As much as I hate re-visiting P1 so soon after refactoring metadata, I wonder if we were too hasty is assuming metadata will always be simple and single valued -- and if so, now would be a good time to change since not to many (if any) people are using it yet.
Duane is gone for a couple weeks, but in talking to him yesterday about this, he agreed in switching from the I*Model interfaces to using metadata.
Let me know what you all think.
Jim
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