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Re: [xml-dev] XML Schema as a data modeling tool

Hi Hans-Juergen,

I think you've mostly understood what I am implying, but this does not have to be a completely comprehensive model for it to be work.  You can start with a single small domain (like Phone numbers, devices and people) and expand from there to build a set of models and systems driven by those models over time.  Remember, that even conventional large grained modelling artifacts have this exact same problem of semantic interpretation and scope.  When I  write up a XSD describing a set of data it does not mean that any of the semantics of that model will be well understood by anyone else without some form of documentation.  However, the fine grained metadata model I described becomes more and more self documenting over time. At some point you may have physical performance requirements coupled to artifacts, and / or you may have security authorization requirements coupled to them, and / or you may have GUI display requirements coupled to them.  All of these form a more complete picture off the usage of the individual pieces then any isolated ER diagram or UML diagram or XSD, or DDL.  You can focus on a specific context and domain or you can look beyond that and see how changes and usage of the model impact other areas of concern.

So, in the end, I'm not sure this is a new layer.  Parts of it might be, in the sense that this can be recursive and the model can describe itself and in most organizations that level of abstraction is not normally formally documented.  What is more important to me is that there are not necessarily well defined boundaries between any of the parts of the complete metadata collection.  Anyone willing to work with the metadata can find all the assumptions without being confined to the single XSD that was dropped on their e-mail at the start of the project.  

And yes, there is not necessarily a boundary between the "Enterprise" and the rest of the semantic web.  One of the neat things you will see people who work with molecular genomics do is build models that not only use external metadata collections but depend on them.  Want to know what BRCA2 means as a gene?  Well, there are many external resources we can go to to drag that in as needed and depending on our context. So, if I'm doing sequence assembly I can recognize the nucleotides that make up that gene, and if I'm preparing a research paper I can more easily find and cite other papers that support my theories on how BRCA2 influences cancer formation. Share meaning is always difficult and the more integration points you have between your modelling artifacts the easier it will be to find the shared meaning.

The pull and push into this type of model should be  no different than any other set of models.  If your organization accepts submissions of external XSDs then those may end up becoming part of the model.  If you publish an XSD documenting an interface then you can version portions of the model and export an XSD that documents that version of the model.  This all does depend on transforms, some of which can now be automated instead of requiring that some human now sit down with the DDL of some portion of the database model to figure out what the XSD should look like to map to it.

Peter Hunsberger

On Sat, Oct 5, 2013 at 12:23 AM, Hans-Juergen Rennau <hrennau@yahoo.de> wrote:
Peter, your thoughts are so far-reaching that a certain problem of communication easily arises, as terms acquire a weight and meaning not immediately obvious to everyone. This may apply to both words which are key in your concept, "model" and "metadata". So it is more impressions, not yet real understanding, what I manage to collect. But here I record them, and they are organized around single words.

Word "comprehensiveness". I feel that the model you are thinking about is extremely comprehensive: ready to ingest just about any metadata about just about anything (business processes, infrastructure, ...). Almost a container of metadata.

Word "layer". As a result, the model is less a single model in the conventional sense, but a layer - a new (?) "model layer", which you implicitly claim to be as fundamental as the conventional "persistence layer" and "application layer". What distinguishes a (conventional) model from a model layer? The former is a centralized and closed structure, growing by a "pull" process - additions are deliberate and selective; the latter is decentralized and open, growing by a "push" process - whenever a certain kind of artifact is created and made accessible, it is automatically added to the layer. (Yes, of course, this way of putting it reminds of the semantic web and RDF.)

Word "coherence". John's concern about the sanity of "merging them [data models] into a single data model" reflects the view of distinct models which can only be integrated by an effort of adaptation etc. From this view point a "model layer" is as incoherent as the persistence layer - a mere collection of models. But I think the core of your vision is a new kind of coherence, enabled by a uniform navigational model, which is supplied by the graph database approach. Thanks to this coherence, anything added to the model layer is immediately addressable, explorable, usable - so-to-speak "self-integrating".

Word "transformation". As your model is essetially a model of metadata, the transition to usable artifacts (e.g. WSDLs, database definitions etc.) is the result of "search+transform" - collecting the appropriate metadata, exploring what they imply, and materialize those implications into artifacts.

What I wonder about is the role of vocabularies and structural patterns. The fact of a superb navigational model does of course not yet guarantee usefulness - it requires an understanding of the "words" you encounter during your navigation (traversals, you would say, probably). So do vocabularies, or ontologies, play a crucial role in the construction of the Enterprise ready model? And do standard structures, which would be comparable to complex types in XSD, describing the assembly of complex units  from building blocks?

Thank you for giving us these glimpses. Should I be completely off the track in my attempts to approach some understanding, perhaps you give me a warning.

(or Hans, just as you like)

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